ICSE Class 9 Chemistry Sample Question Paper

ICSE Class 9 Chemistry Sample Question Paper 10 with Answers

Section -1
(Attempt all questions from this section)

Question 1.
(a) Fill in the blanks with the correct choice given in brackets.
(i) ………….. . does not support combustion. [hydrogen/oxygen]
(ii) A reducing agent is an………………… of electrons. [acceptor/donor]
(iii) The reaction of photosynthesis is an…………… reaction, [endothermic/exothermic]
(iv) …………. water forms lather with soap. [Hard /Soft]
(v) The…………… temperature is called absolute zero. [+ 273°C/- 273°C]
Answer:
(i) Hydrogen
(ii) Donor
(iii) Endothermic
(iv) Soft
(v) – 273°C

(b) Choose the correct answer from the options given below :
(i) (Choose the air pollutant which is non-acidic.
(A) NO₂
(B) SO₂
(C) SO₃
(D) Ozone
Answer:
(D) Ozone                                              ‘

(ii) Choose the odd one.
(A) HCl
(B) H₂CO₃
(C) HNO₃
(D) H₂SO₄
Answer:
(A) HCl

(iii) On adding water to sodium, the solution formed is :
(A) Neutral
(B) Alkaline
(C) Acidic
(D) Amphoteric
Answer:
(B) Alkaline

(iv) According to Boyle’s law, as the pressure increases, the volume :
(A) Increases
(B) Decreases
(C) Remains the same
(D) First increases and then decreases
Answer:
(B) Decreases

(v) In the element ₁₁Na²³,11 represents :
(A) Mass number
(B) Atomic number
(C) Number of neutrons
(D) None of the above
Answer:
(B) Atomic number

(c) Give the valency and the formula of the following radicals :
(i) Sulphate
(ii) Sulphite
(iii) Sulphide
(iv) Carbonate
(v) Ammonium
Answer:

	Formula	Valency
(i)	SO42-	-2
(ii)	SO32-	-2
(iii)	S2-	-2
(iv)	CO32-	-2
(v)	NH4-	+1

(d) An element ‘M’ has three electrons more than the noble gas. Give the formula of its.
(i) Chloride
(ii) Sulphate
(iii) Hydroxide
(iv)  Phosphate
(v) Oxide
Answer:
The outermost shell of all the noble gases is complete. Thus, its valency is zero. ‘M’ has three electrons more than the noble gas. Thus, the valency of the element ‘M’ is +3.
(i) MCl₃
(ii) M₂(SO₄)₃
(iii) M(OH)₃
(iv) MPO₄
(v) M₂O₃                                                                                                    ‘

(e) Correct the following statements.
(i) A molecular formula represents an element.
(ii) The molecular formula of water (H₂O) represents nine parts by mass of water.
(iv) A balanced equation obeys the law of conservation of mass and so does an imbalanced equation.
(v) A molecule of an element is always monoatomic.
(vi) CO and Co both represent cobalt.
Answer:
(i) A molecular formula represents a molecule.
(ii) Molecular formula of water (H₂O) represents eighteen parts by mass of water.
(iii) A balanced equation obeys the law of conservation of mass, while an unbalanced equation does not obey this law.
(iv) A molecule of an element is not always monoatomic.
(v) CO and Co represent carbon monoxide and cobalt, respectively.

(f) (i) What is a solubility curve ?
(ii) Write down two applications of solubility curve.
(iii) 12 g of a saturated solution of potassium chloride at 20°C, when evaporated to dryness, leaves a solid residue of 3 g. Calculate the solubility of potassium chloride.
Answer:
(i) A solubility curve is a line graph that plots changes in solubility of a solute in a given solvent against changing temperature.

(ii) Applications of solubility curve :
1. Shape of the curve indicates how the solubility of the given substance in a solvent varies with change in temperature. The solubility of a substance at a particular temperature can be determined from the curve.
2. The effect of cooling of hot solutions of different substances can be found from the curves.

(iii) Weight of water in solution = 12g – 3g = 9g
9g of water dissolves 3g of solid
Therefore 100 g of water will dissolve = \(\frac{3}{9} x 100 = 33.3 g\)
Solubility of KCl in water at 20°C is 33.3 g.

(g) Give reasons for the following.
(i) Electrovalent compounds conduct electricity in molten or aqueous state.
(ii) Electrovalent compounds have high melting and boiling points, while covalent compounds have low melting and boiling points.
(iii) 1. Electrovalent compounds dissolve in water, whereas covalent compounds do not.
2. Polar covalent compounds conduct electricity.
3. Electrovalent compounds are usually hard crystals yet brittle.
Answer:
(i) 1. They are good conductors of electricity in the fused or aqueous state because electrostatic forces of attraction between ions in the solid state are very strong, and these forces weaken in the fused state or in the solution state. Hence, ions become mobile.

2. In electrovaient compoimds, there exists a strong force of attraction between the oppositely charged ions, and a large amount of energy is required to break the strong bonding force between ions. So, they have high boiling and melting points. In covalent compounds, weak forces of attraction exist between the binding molecules, thus less energy is required to break the force of binding. So, they have low boiling and melting points.

(ii) 1. As water is a polar compound, it decreases the electrostatic forces of attraction, resulting in free ions in aqueous solution. Hence, electrovalent compounds dissolve. Covalent compounds do not dissolve in water but dissolve in organic solvents. Organic solvents are non-polar; hence, these dissolve in non-polar covalent compounds.

2. Polar covalent compounds conduct electricity because they form ions in their solutions.

3. Electrovaient compounds are usually hard crystals yet brittle because they have strong electrostatic forces of attraction between their ions which cannot be separated easily.

(h) Match Column A with Column B.

	Column A	Column B
(i)	Plaster of Paris	(A) Electrovalent compound
(ii)	Nad	(B) Polar compound
(ii)	Nad	(B) Polar compound
(v)	Hydrogen chloride	(E) Non polar compound

Answer:
(i) (D)
(ii) (A)
(iii) (E)
(iv) (B)
(v) (C)

Section – II
(Attempt any four questions from this section)

Question 2.
(a) Explain the Rutherford’s alpha particles scattering experiment with the help of a diagram.
(b) How temporary hardness’s removed by Clark’s process and also explain why removal of temporary hardness by boiling water is not a practical method ?
(c) According to the activity series, which of the following can successfully displace hydrogen ? K/Na/Pb/Ag/Pt/Fe/Al.
Answer:
(a) In 1911, Earnest Rutherford, a scientist from New Zealand, overturned Thomson’s atomic model by his gold foil experiment. His experiment demonstrated that the atom has a tiny massive nucleus. It thus rejected Thomson’s model of the atom.
Rutherford’s scattering experiment
1. Rutherford selected a gold foil as he wanted a very thin layer.
2. In his experiment, fast-moving alpha particles were made to fall on a thin gold foil.
3. Alpha particles are helium ions with +2 charges and have a considerable amount of energy.
4. These particles were studied by the flashes of light they produced on striking a zinc sulphide screen.
5. He expected the alpha particles to pass through the gold foil with little deflections and to strike the fluorescent screen.

Main features of Rutherford’s theory of atom are :
1. There is a positively charged centre in the atom called the nucleus in which nearly all the mass of the atom is concentrated.
2. Negatively charged particles called electrons revolve around the nucleus in paths called orbits.
3. The size of the nucleus is very small as compared to the size of the atom.
4. His model can be compared to the solar system, where the planets are compared with electrons and the sun with the nucleus.

(b) Removal of temporary hardness by Clark’s process is also known by the name by addition of lime. In this method lime is first thoroughly mixed with water in a tank and fed into another tank containing the hard water. Revolving paddles thoroughly mix the two solutions. Most of the calcium carbonate settles down. If there is any solid left over, it is removed by a filter. In this process the following reactions takes place.
Ca(HCO₃)₂ + Ca(OH)₂ → 2CaCO₃ + 2H₂O
Mg(HCO₃)₂ + Ca(OH)₂ MgCO₃ + CaCO₃ + 2H₂O
Temporary hardness is called temporary because the temporary hardness of water can be removed just by boiling. But it is not a practical method to do, because it is slow and very costly.

(c) K and Na can displace hydrogen from acids by reacting violently.
Pb displaces hydrogen from only hot concentrated acids.
Ag and Pt do not displace hydrogen from acids at all.
Fe displaces hydrogen gently from acids.
A1 displaces hydrogen from acids vigorously.

Question 3.
(a) Write a note on discovery of protons and also write two properties of anode ray.
Answer:
(a) Goldstein scientist noticed another set of rays travelling in a direction opposite to that of cathode rays. These rays travel from anode to cathode. He called these rays as canal rays since these rays passed through holes or “canals” in the cathode. These rays were named as positive rays or anode rays. Anode rays travel in a straight line and are deflected by electric and magnetic fields but in a direction opposite to that of the cathode rays. This shows that these rays consist of positively charged particles called protons.

Properties of anode rays :
1. Anode rays consist of minute material particles and hence produce mechanical effects.
2. These rays produce fluorescence on a zinc sulphide screen.

(b) Under what conditions can hydrogen be made to combine with ?
(i) Nitrogen
(ii) Chlorine
(iii) Sulphur
(iv) Oxygen
Name the products in each case and write the equation for each reaction.
Answer:
(i) Three volumes of hydrogen and one volume of nitrogen react at temperature 450- 500°C and pressure 200-900 atm in the presence of a finely divided iron catalyst with molybdenum as promoter to give ammonia.
\(\mathrm{N}_{2}+3 \mathrm{H}_{2} \rightleftharpoons 2 \mathrm{NH}_{3}\)

(ii) Equal volumes of hydrogen and chlorine react slowly in diffused sunlight to form hydrogen chloride.
H₂ + Cl₂ → 2HCl

(iii) Hydrogen gas on passing through molten sulphur reacts to give hydrogen sulphides.
H₂ + S → H₂S

(iv) Hydrogen bums in the presence of electric spark with a ‘pop’ sound in oxygen and with a blue flame forming water.
2H₂ + O₂ → 2H₂O

(c) The formula of the chloride of a metal ‘M’ is MCl₂. State the formula of its :
(i) Carbonate
(ii) Nitrate
(iii) Hydroxide.
Answer:
(i) MCO
(ii) M(NO_s)₂
(iii) M(OH)₂

Question 4.
(a) Two neutral gases ‘A’ and ‘B’ undergo a synthesis reaction to form a gas ‘C’.
(i) Identify ‘A’, ‘B’ and ‘C’.
(ii) Name the process by which gas ‘C’ is manufactured. Give the balanced chemical equation along with the conditions.
(iii) What do you observe when gas ‘C comes in contact with ?
(1) Moist red litmus paper,
(2) Concentrated hydrochloric acid.
Answer:
(a) (i) A – Nitrogen B – Hydrogen C – Ammonia
(ii) Gas ‘C’ is manufactured by the Haber process.
N₂ + 3H₂ → 2NH₃ + Heat

Favourable conditions :

1. Temperature should be between 450°C and 500°C.
2. Pressure should be high (200-1000 atm.).
3. Promoter used should be molybdenum.

(iii) It turns moist red litmus blue.

(b) What do you understand by the combining capacity of atoms? Explain with examples.
Answer:
An atom of each element has a definite combining capacity called its valency. The combining capacity of the atoms, i.e., their tendency to react and form molecules with atoms of the same or different elements, was explained as an attempt to attain a fully filled outermost shell of electrons.

This is done by sharing, gaining or losing electrons. For example, lithium and sodium atoms contain one electron each in their outermost shell; therefore, each of them can lose one electron to have 8 electrons in their outermost shell. So, they are said to have valency = 1.

(c) What is meant by :
(i) electronic configuration,
(ii) atomic number
(iii) atomic mass number
Answer:
(i) Electronic configuration is the arrangement of electrons in the atomic or molecular orbitals of atoms or molecules.
(ii) Atomic number of elements is the number of protons in an atom of the element.
(iii) Atomic mass of an element is the total mass of electrons, protons and neutrons in one atom of the element.

Question 5.
(a) What is the effect of increasing and decreasing pressure on the solubility of a gas in a liquid ?
Answer:
On increasing pressure the solubility of a gas in a liquid increases whereas, on decreasing pressure the solubility of a gas in a liquid decreases. This shows the mass of a given volume of a gas which dissolves in liquid at constant temperature is directly proportional to the pressure on the surface of the liquid and thus in accordance with Henry’s law.

(b) State which salts increase in weight, decrease in weight or remain the same when exposed to the atmosphere.
(i) Sodium hydroxide
(ii) Ferric chloride
(iii) Green vitriol
(iv) Cone, sulphuric acid
Answer:
(i) Increases
(ii) Increases
(iii) Decreases
(iv) Increases

(c) Why is it necessary to compare gases at STP ?
Answer:
The volume of a given mass of dry enclosed gas depends on the pressure of the gas and the temperature of the gas in Kelvin, so to express the volume of the gases, we compare these to STP.

Question 6.
(a) How does the modern atomic theory contradict and correlate with Dalton’s atomic theory ?
Answer:
Dalton was right that atoms take part in chemical reactions.
Comparisons of Dalton’s atomic theory with the modem atomic theory.
Dalton’s atomic theory :
1. Atoms are indivisible.
2. Atoms of the same element are similar in every respect.
3. Atoms combine in a simple whole number ratio to form molecules.
4. Atoms of different elements are different.
5. Atoms can neither be created nor be destroyed.

Modem atomic theory :
1. Atoms are no longer indivisible and consist of electrons, protons, neutrons and even more sub-particles.
2. Atoms of the same element may differ from one another called isotopes.
3. Atoms of different elements may be similar called isobars.
4. Atoms combine in a ratio which is not a simple whole number ratio; e.g., in sugar, the C₁₂H₂₂O₁₁ ratio is not a whole number ratio.

(b) Classify the following as homogeneous or heterogeneous and give one example of each :
(i) Solid-Solid
(ii) Solid-Liquid
(iii) Gas-Gas
(iv) Liquid-Liquid
(v) Gas-Solid
Answer:

Constituents of mixture	Nature of mixture	Examples
(i) Solid-Solid	Homogeneous	Alloys
(ii) Solid-Liquid	Homogeneous	Salt in water
(iii) Gas-Gas	Homogeneous	Air
(iv) Liquid-Liquid	Homogeneous	Milk in water
(v) Gas-Solid	Heterogeneous	Smoke

(c) Draw the orbit structure for each of the following compounds :
(i) Methane [H = 1, C = 6]
(ii) Magnesium chloride [Mg = 12, Cl = 17]
Answer:
(i) Orbit structure of methane

(ii) Orbit structure of magnesium chloride

The two electrons lost by a magnesium atom are gained by chlorine atoms to produce a magnesium ion and two chloride ions.

Question 7.
(a) Give reasons for the following :
(i) Hydrogen shows dual nature
(ii) Gases diffuse rapidly.
(iii) Rivers and lakes do not freeze easily ?
Answer:
(i) Hydrogen shows dual nature because it resembles the alkali metals of group LA and the halogens of group VELA.
(ii) Gases have maximum intermolecular space. Therefore, when two gases are brought in contact, they readily fill the intermolecular spaces and form a homogeneous mixture.
(iii) Rivers and lakes have a large amount of water, and water has high specific heat capacity due to which it does not freeze easily. Even if water freezes, it freezes into ice on the surface (at the top) of rivers and lakes. Water is present below because of anomalous expansion of water.

(b) Name the solvent for the following precipitates :
(i) Silver chloride
(ii) Lead sulphate
(iii) Lead chloride
Answer:
(i) Ammonium hydroxide
(ii) Ammonium acetate
(iii) Soluble in hot water

(c) What is latent heat of vapourization ?
Answer:
Latent heat of vapourization is the heat energy required to change 1 kg of a liquid to a gas at atmospheric pressure at its boiling point.

ICSE Class 9 Chemistry Question Papers with Answers

ICSE Class 9 Chemistry Sample Question Paper 9 with Answers

Section -1
(Attempt all questions from this section)

Question 1.
(a) Fill in the blanks with the correct choice given in brackets.
1. Mass number of an element is the total number of………………… and neutrons present in its nucleus.  [protons/electrons]
2. ……………….. and ………………… are bridge elements. [Li and Mg/Na and Ca]
3. The chemical reaction in which heat is liberated is known as………………… [endothermic/exothermic]
4. The electrons present in the ………………. shell of an atom are called valence electrons. [innermost/outermost]
5. The molecular formula of quick lime is……………… [Ca(OH)₂/CaO]
Answer:
(i) Protons
(ii) Li and Mg
(iii) Exothermic
(iv) Outermost
(v) Ca(OH)₂

(b) Choose the correct answer from the options given below :
(i) The gas that prevents haemoglobin from carrying blood to different parts of the body is :
(A) Sulphur dioxide
(B) Carbon monoxide
(C) Hydrogen sulphide
(D) Methane
Answer:
(B) Carbon monoxide

(ii) According to Mendeleev’s periodic law the physical and chemical properties of elements are a periodic function of their :
(A) Atomic number
(B) Atomic masses
(C) Atomic weight
(D) Mass number
Answer:
(B) Atomic masses

(iii) The specific value of the amount of heat energy required by ice to change into water is :
(A) 336 J/g
(B) 80 cal/g
(C) 2268 J/g
(D) Both A and B
Answer:
(D) Both A and B

(iv) The graph of PV vs. P for a gas is :
(A) Parabolic
(B) Hyperbolic
(C) A straight line parallel to x
(D) A straight line parallel to y axis
Answer:
(C) A straight line parallel to x

(v) The property which is a characteristic of an equivalent compound is :
(A) They are weak electrolyte.
(B) They are non-volatile.
(c) They conduct electricity in the solid state.
(D) They are soluble in organic solvents.
Answer:
(B) They are non-volatile.

(c) Name the gas evolved in each of the following cases :
(i) When zinc reacts with dilute sulphuric acid.
(ii) When copper carbonate decomposes on heating.
(iii) When chlorine is exposed to sunlight.
(iv) When an electric current is passed through accumulated water.
(v) When nitrogen tetraoxide is heated.
Answer:
(i) Hydrogen
(ii) Carbon dioxide
(iii) Oxygen
(iv) Hydrogen and Oxygen
(v) Nitrogen dioxide

(d) Give a reason for each of the following :
(i) Why elements of group numbers 3 to 12 are known as transition elements ?
(ii) Why the valency of all elements in a group is same ?
(iii) Why hydrogen is called inflammable air ?
(iv) Why washing soda when exposed to dry air becomes a monohydrate ?
(v) Why group 1 elements in periodic table are known as alkali metals ?
Answer:
(i) Elements of group numbers from 3 to 12 are known as transition elements because they have their two outermost shells incomplete.

(ii) Since elements in a particular group have an equal number of electrons in their respective valence shells, thus the valency of all elements in a group is same.

(iii) Hydrogen gas is called inflammable air because of its combustible nature.

(iv) Washing soda when exposed to dry air becomes a monohydrate because it loses its water of crystallisation.

(v) Group 1 elements are known as alkali metals because they react with water to form their hydroxides which are strong alkalies.

(e) What do you observe when :
(i) Alkali metals react with water.
(ii) Halogens react directly with metal.
(iii) Aluminium reacts with steam.
(iv) The temperature of sodium nitrate, potassium nitrate and potassium bromide is increased.
(v) Iron nails are added to blue coloured copper sulphate solution.
Answer:
(i) They react with water to produce hydrogen.
2M + 2H₂O → 2MOH + H₂ Where M is alkali metal.
(ii) They form metal halides or salts.
(iii) It liberates hydrogen.
(iv) When the temperature is increased their solubility decreases.
(v) The blue colour of the solution fades and eventually turns into light green due to formation of ferrous sulphate.

(f) (i) State Charle’s law.
(ii) Write 2 behaviour and characteristics properties of gases.
(iii) Give the mathematical form of the Boyle’s law.
Answer:
(i) Charle’s law may be stated as volume of a given mass is directly proportional to its absolute temperature, if the pressure remains constant.
\(\frac{\mathrm{V}_{1}}{\mathrm{~T}_{1}}=\frac{\mathrm{V}_{2}}{\mathrm{~T}_{2}}=\mathrm{K} = K\) (at constant pressure)
Where V₁ is volume occupied by gas 1 at temperature T₁ and V₂ is volume occupied by gas 2 at temperature T₂.

(ii) Behaviour and characteristics properties of gases are as follows :

1. Gases have low density : The number of molecules per unit volume in a gas is very small as compared to solids and liquids. Gases have large inter molecular space between their molecules. Therefore they have low density.

2. Gases exert pressure in all directions : The moving particles of gas collide with each other and also in the container that is why they exert pressure in all directions.
\(\mathrm{V}_{1}=\frac{\mathrm{K}}{\mathrm{P}_{1}}\) (at constant temperature)
Or P₁V₁ = P₂V₂

(g) (i) Balance each of the following chemical equations given below :
1. KMnO₄ + H₂SO₄ → K₂SO₄ + MnSO₄ + H₂O + [O]
2. Al₂O₃ → Al + O₂
Answer:
1. 2KMnO₄ + 3H₂SO₄ → K₂SO₄ + 2MnSO₄ + 3H₂O + 5[O]
2. AIP3 → 4A1 + 3O₂

(ii) Identify the substance which matches the description given below :
(1) It catches fire and bums with a lilac-coloured flame and produces hydrogen when reacted with water.
(2) It acts as a dehydrating agent and removes water molecule from blue vitriol.
(3) The metals that cannot displace hydrogen from dilute hydrochloric acid.
Answer:
1. Potassium when reacts with water bums with a lilac coloured flame.
2K + 2H₂O → 2KOH + H₂

2. Conc. H₂SO₄ removes water molecules from blue vitriol and acts as a dehydrating agent.

3. Metals like Cu, Ag and Au.

(h) Match Column A with Column B.

Column A	Column B
(i) Alkaline earth metals	(A) Cone. H2SO4
(ii) Green house gases	(B) Argon, Neon, Helium
(iii) Dehydrating agent	(C) K, L, M, N, O, P, Q
(iv) Inert gases	(D) CO2, N2O
(v) Caustic soda	(E) NaOH

Answer:
(i) (C)
(ii) (D)
(iii) (A)
(iv) (B)
(v) (E)

Section – II
(Attempt any four questions from this Section)

Question 2.
(a) Consider M is any alkali metal. Give the general equation as well as explanation of the following :
(i) When M reacts with acids.
(ii) When M reacts with water.
(iii) When M reacts with air.
Answer:
(a) (i) Li, Na, K, Rb, Cs, Fr are all alkali metals.
When M reacts with acids the following action takes place.
2M + 2HCl → 2MCl + H₂
They react violently with dil. HCl and dil. H₂SO₄ to produce hydrogen.

(ii) When M reacts with water the following action takes place.
2M + 2H₂O → 2MOH + H₂

(iii) When M reacts with air the following action takes place.
4M + O₂ → 2MO
MO +H₂O → 2MOH
They react rapidly with oxygen and water vapour in the air.

(b) Write the balanced chemical equation of the following :
(i) Lead nitrate when heated.
(ii) Ammonium and hydrogen chloride combines.
(iii) Reaction of iron with chlorine.
Answer:
(i) \(2 \mathrm{~Pb}\left(\mathrm{NO}_{3}\right)_{2} \stackrel{\text { (Heät) }}{\longrightarrow} 2 \mathrm{PbO}+4 \mathrm{NO}_{2}+\mathrm{O}_{2}\)
Lead nitrate decomposes on heating leaving a yellow residue lead monoxide, brown
gas nitrogen dioxide and colourless gas oxygen.

(ii) Ammonium and hydrogen chloride both compounds combine to form a new
compound ammonium chloride.
NH₃(g) + HCl(g) → NH₄Cl(s)

(iii) When iron reacts with chlorine iron (Ill) chloride salt is formed.
2Fe + 3Cl₂→ 2FeCl₃

(c) Draw the orbit structure for each of the following compounds and also write their electronic configuration and valency.
(i) Boron
(ii) Neon
(iii) Fluorine
(iv) Hydrogen
Answer:

Question 3.
(i) Write two similarities between hydrogen and halogens.
(ii) How hydrogen is produced from cold water ?
Answer:
(i) Similarities between hydrogen and halogen are :

1. Hydrogen and halogen have one electron less than the nearest inert gas.
2. Both have valency 1, they accept 1 electron of the nearest inert gas to attain the electronic configuration.

(ii) Among the reactive metals sodium reacts with cold water and form their corresponding hydroxides evolving hydrogen. The reaction is exothermic and vigorous.
2Na + 2H₂O → 2NaOH + H₂

(b) (i) What is Newland’s law of octaves ?
(ii) Write two drawbacks of Newland’s law of octaves ?
(iii) Write two merits of Newland’s classification.
Answer:
(i) According to Newland’s law of octaves, “When elements are arranged by increasing atomic mass, the properties of every eighth element starting from any element are a repetition of the properties of the starting element”.

(ii) Drawbacks of Newland’s law of octaves are :
1. This classification did not work with heavier elements i.e., those lying beyond calcium. As more and more elements are discovered, they could not fit into Newland’s Law.
2. Iron which resembles, with cobalt and nickel in properties has been placed far away from those elements.

(iii) 1. It relates the properties of the elements to their atomic masses.
2. For the first time it is shown that there is a distinct periodicity in the properties of elements.

(c) Write the merits of the modem periodic table.
Answer:
Merits of the modem periodic table are as follows :
1. It is based on atomic number, which is an even better fundamental property compared to atomic mass.
2. Position of an element in the table is related to its electronic configuration.
3. It shows regular changes in properties of elements on moving across a period or down a group.
4. Modem periodic table is easier to remember, understand and reproduce.

Question 4.
(a) 120 cm³ of a gas is taken at 27.3 K. The temperature is then raised to 0°C. What is the new volume of the gas ? The temperature is kept constant.
Answer:

(b) Calculate the final volume of a gas ‘X’ if the pressure of the gas, originally at STP, is doubled and its temperature is made three times.
Answer:

(c) Calculate the relative molecular mass of each of the following :
(i) Ammonia (NH₃)
(ii) Tricalcium phosphate Ca₃(PO₄)₂
Answer:
(i) To find the molecular mass of NH₃, the first step is to look up the atomic masses of nitrogen and hydrogen.
Atomic mass of nitrogen = 14.0067 Atomic mass of hydrogen = 1.00794
Next, multiply the atomic mass of each atom by the number of atoms in the compound. There is one nitrogen atom (no subscript is given for one atom). There are three hydrogen atoms, as indicated by the subscript.
Molecular mass = (1.x 14.0067) + (3 x 1.00794)
Molecular mass = 14.0067 + 3.02382 = 17.0305

(ii) From the periodic table, the atomic masses of each element are :
Ca = 40.078 P = 30.973761
O = 15.9994
The tricky part is figuring out how many of each atom are present in the compound. There are three calcium atoms, two phosphorus atoms, and eight oxygen atoms.

To get the part of the compound which is in parentheses, multiply the subscript immediately following the element symbol by the subscript that closes the parentheses.
Molecular mass = (40.078 x 3) + (30.97361 x 2) + (15.9994 x 8)
Molecular mass = 120.234 + 61.94722 + 127.9952 = 310.17642 = 310.18

Question 5.
(i) Write the electronic configuration of the following :
(1) { }_{20}^{40} \mathrm{Ca}
(2) { }_{32}^{16} \mathrm{S}
(ii) What is an atom ?
(iii) What are protons ?
Answer:
(i) 1. Is² 2s² 2f 3s² 3p⁶ 4s²
2. Is² 2s² 2f 3s² 3p⁴

(ii) An atom is the smallest particle of an element that exhibits all the properties of that element. It may or may not exist independently but takes part in every chemical reaction.

(iii) Proton may by defined as a sub-atomic particle having mass 1 amu, e., equal to hydrogen atom and has unit positive charge.

(b) (i) What do you understand by the term Isobars ? Give examples.
(ii) What is a neutron ?
(iii) What is an atom ? Write its structural parts.
Answer:
(i) Isobars are atoms of different elements with the same mass number, but different atomic numbers. Since the properties of elements depend upon atomic number, so they have both different physical and chemical properties.
Examples : ⁴⁰S, ⁴⁰C1, ⁴⁰Ar, ⁴⁰K and ⁴⁰Ca. The nuclei of these nuclides all contain 40 nucleons; however, they contain varying numbers of protons and neutrons.

(ii) A neutron is a sub-atomic particle or fundamental particle of an atom with no charge and mass almost equal to the mass of proton e., hydrogen atom. Neutron is denoted by pn¹. The subscript 1 represents its mass and subscript 0 represents its electrical charge.

(iii) An atom is built up of a number of sub-atomic particles e., electrons, protons and neutrons. Electron has charge -1, proton has charge +1 and neutron has charge 0. There are two structural parts of an atom-the nucleus and orbits.

(c) How would you distinguish between the following pairs of substances on the basis of tests given in brackets ?
(i) Magnesium (Action of hot water and steam)
(ii) Zinc hydroxide (Action of bases and acids)
(iii) Unknown substance (Action of dilute sulphuric acid)
Answer:
(i) Magnesium reacts slowly with boiling water and forms a base, magnesium hydroxide liberating hydrogen.
Mg + 2H₂O → Mg(OH)₂ + H₂  ↑
Magnesium bums in steam with an intense white light, liberating hydrogen gas and white ash i.e., magnesium oxide.
Mg + H₂O → MgO + H₂ ↑

(ii) Hydroxides of zinc are amphoteric i.e., they react with both bases and acids to give salt and water.
ZnO + 2HCl → ZnCl₂ + H₂O
ZnO + 2NaOH → Na₂ZnO₂ + H₂O

(iii) When dilute sulphuric acid is added to the given unknown substance and then is warmed a colourless gas is evolved with brisk effervescence, and the gas on passing through lime water turns it milky.
Na₂CO_s + H₂SO₄ → Na₂SO₄ + H₂O + CO₂

Question 6.
(a) State whether the property increases, decreases or remains same in the following cases :
(i) Alkali metals reactivity when one moves down the group.
(ii) Atomic size of elements when one moves down a group.
(iii) Metallic character when one moves down a group.
Answer:
(a) (i) Alkali metals are all very reactive and degree of reactivity increases down the group.
Li < Na < K < Rb < Cs

(ii) Size of atoms of successive element increases down the group.
Li < Na < K < Rb < Cs
Atomic size increases

(iii) Metallic character increases as one moves down the group. For example : In group 15, nitrogen and phosphorus are non-metals, arsenic and antimony are metalloids and bismuth is a typical metal.

(b) (i) What is the difference between soft water and hard water ?
(ii) Write three physical properties of water.
Answer:
(i)

Soft water	Hard water
1. It readily forms lather with soap. 2. It contains high amount of sodium. 3. It is not harsh on skin.	1. It does not readily forms lather with soap. 2. It contains high amount of calcium and magnesium. 3. It is harsh on skin

Physical properties of water are :
1. Nature : Pure water is a clear, transparent liquid. It is colourless, odourless and tasteless.
2. Boiling point: Under normal pressure, pure water boils at 100°C. The boiling point of water is affected by pressure, the greater the pressure the higher the boiling point.
3. Freezing point : Pure water freezes at 0°C under pressure. The freezing decreases with increase in temperature.

(c) Write two types of chemical reactions with two examples of each.
Answer:
Two types of chemical reaction are as follows :

1. Direct combination reactions : A reaction in which two or more substances combine to form a single substance is called a combination reaction.
Example 1.
C + O₂ → CO₂ + Heat.
Carbon bums in oxygen to form a gaseous compound carbon dioxide.
Example 2.
Fe + S → FeS
The reaction between iron and sulphur to form iron (II) sulphide.

2. Displacement reactions : A reaction in which more reactive element displaces a less reactive element which result in the formation of its salt solution.
Example 1.
CuSO₄ + Zn → ZnSO₄ + Cu

When zinc is added to copper sulphate solution the displacement reaction takes place and blue colour of the solution fades and becomes colourless.
Example 2.
2KI + Cl₂  → 2KCl + H₂

When chlorine gas is passed through a solution of potassium iodide the colourless solution turns yellow brown as iodine appears.

Question 7.
(i) Complete the following table :

Element	Atomic	Mass no.	P	n	e
A	1	1	1	—	—
B	14	—	17	—	7
C	—	12	12	12	—
D	35	—	17	—	17

(ii) Give the electronic configuration of A, B, C and D.
(iii) Identify A, B, C and D.
(iv) How many valence electrons are present in A, B, C and D ?
(v) What is the valency of A, B, C and D ?
Answer:
(ii) Electronic configuration of A = 1 Electronic configuration of B = 2, 5 Electronic configuration of C = 2, 8, 2 Electronic configuration of D = 2, 8, 7
(iii) A = Hydrogen, B = Nitrogen, C = Magnesium, D = Chlorine
(iv) A = l, B = 5, C = 2, D = 7
(v) A = l, B = 3, C = 2, D = 1

(b) Write the electronic configuration of the following :
(i) Iron (Fe)
(ii) Palladium (Pd)
Answer:
(i) Electronic configuration of iron is :
Is² 2s² If 3s² 3f 3d⁶ 4s²
(ii) Electronic configuration of palladium is :
Is² 2s² 2 f 3s² 3p⁶ 3d¹⁰ 4s² 4 f 4d¹⁰

(c) State the valency of the element having :
(i) 5 electrons in the valence shell.
(ii) Electronic configuration 2, 5.
Answer:
(i) The valency of an element having 5 electrons in the valence shell is 3.
(ii) The valency of an element having 2, 5 electronic configuration is 3.
The valency of an element having 2, 5 electronic configuration is 3 and having 2, 3 electronic configuration is also 3.

ICSE Class 9 Chemistry Question Papers with Answers

ICSE Class 9 Chemistry Sample Question Paper 8 with Answers

Section -1
(Attempt all questions from this section)

Question 1.
(a) Fill in the blanks with the correct choice given in brackets.
(i) Nitric oxide is toxic. …………… [less/more]
(ii) The gaseous material which envelopes the earth is called …………….[atmosphere/ air]
(iii) The lowest region of the atmosphere is called …………………. [troposphere/ stratosphere]
(iv) The stratosphere mainly contains ………… oxygen and ozone.[nitrogen/hydrogen]
(v) Rain water containing H₂SO₄ and HNO₃ is called [acid rain/normal rain]
Answer:
(i) Less
(ii) Atmosphere
(iii) Troposphere
(iv) Nitrogen
(v) Acid rain

(b) Choose the correct answer from the options given below :
(i) Noble gases are :
(A) Monoatomic
(B) Diatomic
(C) Triatomic
(D) None of the above
Answer:
(A) Monoatomic

(ii) Metals below …………. do not rust easily :
(A) Hydrogen
(B) Copper
(C) Potassium
(D) Sodium
Answer:
(B) Copper

(iii) From which of the following metals hydrogen can be prepared :
(A) Copper
(B) Mercury
(C) Both A and B
(D) None of the above
Answer:
(C) Both A and B

(iv) What is the chemical name of bleaching powder ?
(A) Calcium oxychloride
(B) Calcium hypochlorite
(C) Calcium hydroxide
(D) Both A and B
Answer:
(D) Both A and B

(v) Which of the following conditions are true regarding gases ?
(A) Gases exert pressure in all directions.
(B) Gases are not compressible.
(C) Gases have low density.
(D) Both A and C.
Answer:
(D) Both A and C.

(c) List the major health effects of the following pollutants.
(i) Carbon monoxide
(ii) Suspended particulate matter
(iii) Ozone
(iv) CFC
(v) Oxides of nitrogen
Answer:
(i) Reduces oxygen in blood causing retardation and dizziness.
(ii) Small particles get lodged in the lungs and gradually damage the functioning of lungs.
(iii) Burning, etching, watery eyes and lowered resistance to repiratory disease.
(iv) Reduces ozone layer that protects us from the harmful ultraviolet rays of the sun.
(v) Smog produces acid rain that makes children more susceptible to respiratory diseases.

(d) Give reason for each of the following :
(i) Why hydrogen cannot be collected by the downward displacement of air ?
(ii) Why nitric acid cannot be used in the preparation of hydrogen ?
(iii) Why rain water and distilled water do not form concentric rings ?
(iv) Why distilled water when kept in a sealed bottle for a long time leaves etchings on the inside surface of glass ?
(v) Why a salt formed due to a strong base and a weak acid, on dissolving in water, will make a basic solution
Answer:
(i) Hydrogen cannot be collected by the downward displacement of air because it forms an explosive mixture with air.

(ii) Nitric acid cannot be used in the preparation of hydrogen because it is a powerful oxidizing agent, and the oxygen formed due to its decomposition oxidizes the hydrogen to give water, thus defeating the purpose of the reaction.

(iii) Rain water and distilled water do not contain dissolved solids this is the reason they do not form concentric rings.

(iv) Substances that are apparently insoluble in water actually dissolve in it in traces. When distilled water is kept in a glass it dissolves in water and leaves etchings on the inside surface of the glass.

(v) This happens because of hydrolysis, it is a process in which a salt and water react to form an acidic or a basic solution. In this process only those salts hydrolyze that are formed by the reaction of strong base and weak acid and strong acid and weak base.

(e) What do you observe when :
(i) When methane undergoes combustion ?
(ii) When CuSO₄.5H₂O is treated with cone, sulphuric acid.
(iii) When ammonium dichromate is heated ?
(iv) When cone. HCl is added to oxidizing agents like Pb₃O₄, MnO₂ ?
(v) When carbon monoxide is treated with platinum ?
Answer:
(i) Combustion of natural gas is an important source of energy for homes and industry,when methane (natural gas) undergoes combustion large amount of energy is produced which is used in the form of fuels in vehicles.

(ii) When CuSO₄.5H₂O is treated with cone. H₂SO₄, then dehydration takes place and cone, sulphuric acid removes water molecules from blue vitriol.

(iii) When ammonium dichromate is heated it swells up and decomposes violently with flashes of light leaving greenish residue, water vapour and nitrogen is evolved during this reaction.

(iv) When cone. HCl is added to oxidizing agents like Pb₃O₄, MnO₂ it turns moist blue litmus paper red and finally bleaches i.e., decolourizes it.

(v) Carbon monoxide changes into carbon dioxide in the presence of finely divided platinum as catalyst.

(f) Answer the following questions :
(i) What is diffusion ?
(ii) What are the gas laws and write down its standard variables ?
(iii) State Charle’s law in terms of dry gas
Answer:
(i) Diffusion is the process of gradual mixing of two substances, kept in contact, by molecular motion. Inter-particle spaces in a gas are very large. When two gases are brought in contact with each other, their molecules mix with each other in such a manner that a homogeneous gaseous mixture is formed.

(ii) The behaviour of gases under known conditions of pressure, volume and temperature is described by gas laws. The physical behaviour of gases can be described by three standard variables :
(a) Volume (V)
(b) Pressure (P)
(c) Temperature (T)

(iii) It says that volume of a given mass of a dry gas is directly proportional to its absolute temperature, if the pressure remains constant.

(g) Write balanced chemical equations : .
(i) 1. Decomposition of copper nitrate.
2. Thermal dissociation of phosphorus penta chloride.
Answer:
1. \(2 \mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2} \stackrel{\Delta}{\longrightarrow} \mathrm{CuO}+4 \mathrm{NO}_{2}+\mathrm{O}_{2}\)
2. \(\mathrm{PCl}_{5} \stackrel{\Delta}{\longrightarrow} \mathrm{PCl}_{3}+\mathrm{Cl}_{2}\)

(ii) 1. Magnesium bums in oxygen.
2. Hydrogen bums in air or oxygen.
3. Carbon dioxide is passed through lime water.
Answer:
1. 2Mg + O₂ → 2MgO
2. 2H₂ + O₂ → 2H₂O
3. CO₂ + Ca(OH)₂ →CaCO₃ + H₂O

(h) Match Column A with Column B.

Column A	Column B
(i) Binary solution (ii) Silica (iii) Heat is absorbed (iv) Sodium chloride (v) Cathode rays	(A) Endothermic reaction (B) Electrons (C) Have high solubi0ty (D) Has two components (E) Silicon dioxide

Answer:
(i) (D) (ii) (E) (iii) (A) (iv) (C) (v) (B)

Section II
(Attempt any four questions from this section)

Question 2.
(a) An element ‘M’ has three electrons more than the noble gas. Give the formula of its:
(i) Chloride
(ii) Sulphate
(iii) Hydroxide
(iv) Phosphate
Answer:
The outermost shell of all the noble gases is complete. Thus, its valency is zero. ‘M’ has three electrons more than the noble gas. Thus, the valency of the element ‘M’ is + 3.
(i) MCl₃
(ii) M₂(SO₄)₃
(iii) M(OH)₃
(iv) MPO₄

(b) Complete and balance the following equations :
(i) Cu + HNO₃ → ………………….. + ………………. +…………………
(ii) FeSO₄ → ……………. + ………………. + SO₃
(iii) Pb₃O₄ + HCl → PbCl₂ +………………… +……………….
(iv) H₂S + SO₂ → ……………….. + ………………
(v) Ca(NO₃)₂ → CaO + ……………….. + ……………….
(vi) \(\mathrm{Na}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O} \stackrel{\text { heat }}{\longrightarrow} \mathrm{Na}_{2} \mathrm{CO}_{3}+10 \mathrm{H}_{2} \mathrm{O}\)
(c) Draw the orbit structure and electron dot diagrams of NaCl, MgCl₂ and CaO.
Answer:

Question 3.
(a) (i) Write the process of preparation of hydrogen from zinc.
(ii) Write down two tests for oxidizing agents.
Answer:
(i) Hydrogen can be prepared by action of steam on metals such as zinc. The following reaction occurs :
Zn + H₂O → ZnO + H₂

1. In the above reaction hydrogen is liberated and zinc is converted to zinc oxide.
2. Zinc is less reactive i.e., it reacts only when it is heated and steam is passed over it.
3. Zinc oxide is yellow when it is hot but white when it is cold.

(ii) Test for oxidizing agents :
1. On heating strongly, they liberate oxygen, which rekindles a glowing splinter.
2. On treating with acidified potassium iodide solution, they liberate iodine, which imparts a blue colour to freshly-prepared starch solution.

(b) What is a periodic table and write down the essential features of Mendeleev’s periodic table ?
Answer:
Periodic table is a chart of elements prepared in such a way that elements with similar properties occur in the same vertical column or group.

Mendeleev’s periodic table contains vertical columns called groups and horizontal rows called periods. Features of his periodic table are as follows :
1. There are in all eight groups i.e., Group I to Group VET Each of these groups from I to VII is divided into two sub-groups : A and B. Group VIII has no sub-group. Inert gases were not known at that time.

2. All elements of a sub-group have similar properties and show the same valency, which is equal to the group number. In a period elements gradually change from metallic to a non-metallic character decreases as one moves from left to right across the horizontal row.

3. In a period, elements gradually change from metallic to non-metallic character or metallic character decreases as one moves from left to right across the horizontal row.

(c) (i) Why is it so that oxides of elements become increasingly basic in character moving in the same direction ?
(ii) State the modified periodic law of Mendeleev.
Answer:
(i) It is on account of gradual increase in metallic character of elements from top to bottom that oxides of elements become increasingly basic in character moving in the same direction. Metallic character increases as one moves down the group.
(ii) The physical and chemical properties of all elements are the periodic function of their atomic numbers.

Question 4.
(a) 16 g of oxygen gas is enclosed in a 1 dm³ flask at 25°C. Calculate the pressure exerted by the gas, if the molecular mass of any gas occupies 22.4 litres at S.T.P.
(b) At what centigrade temperature will the volume of a gas at 0°C triple itself if the pressure remains constant ?
(c) Explain the significance of Boyle’s law and its graphical verification.
Answer:
(a) Oxygen is a diatomic gas.
Its molar mass is 16 x 2 = 32 g
So, 32 g of oxygen occupies 22.4 dm³ at S.T.P.

(c) Significance of Boyle’s law : On increasing pressure, volume decreases. The gas becomes denser. Thus, at constant temperature, the density of a gas is directly proportional to its pressure. Atmospheric pressure is low at high altitudes, so air is less dense. Hence, a lesser quantity of oxygen is available for breathing. This is the reason why mountaineers have to carry oxygen cylinder with them.

Graphical verification of Boyle’s law :
1. V Vs. \(\frac{1}{\mathrm{P}}\)
Variation in volume (V) plotted against pressure (1/P) at a constant temperature – a straight line passing through the origin is obtained.

2. V Vs. P : Variation in volume (V) plotted against pressure (P) at a constant temperature – a hyperbolic curve in the first quadrant is obtained.

3. PV Vs. P : Variation in PV plotted against pressure (P) at a constant temperature – a straight line parallel to the X-axis is obtained.

Question 5.
(a) (i) What do you mean by isobars ?
(ii) Why are isotopes of an element chemically alike ?
(iii) Why carbon-14 and tritium are known as radio-isotopes ?
Answer:
(a) (i) Isobars are atoms of different elements with the same mass number, but different atomic numbers. Since the properties of elements depend upon atomic number, so they have both different physical and chemical properties.

(ii) As we know that chemical properties are determined by the electronic configuration of an atom. Isotopes have the same atomic number Z i.e., the same number of electrons and proton and hence the same electronic configuration. Thus isotopes of an element are chemically alike.

(iii) Isotopes like tritium, carbon-14 illustrate another difference in physical properties that can occur between isotopes as they are radioactive. The extra neutrons in their nuclei cause them to be unstable so the nuclei break up spontaneously emitting certain types of radiations. Thus carbon-14 and tritium are known as radio-isotopes.

(b) Give reason:
(i) Covalent compounds are insoluble in water but soluble in organic solvents.
(ii) Electrovalent compounds are soluble in water but insoluble in organic solvents.
(iii) Zinc granules are used in the laboratory preparation of hydrogen over pure zinc.
(iv) Name some reducing agents and write the tests for reducing agents.
Answer:
(i) As organic solvents are non-polar, hence, these compounds dissolve in non-polar compounds.
(ii) As water is a polar compound, it decreases the electrostatic forces of attraction, resulting in free ions in aqueous solution. Hence electrostatic compounds dissolve in water.
(iii) It is because the impurity present in granulated zinc is copper, and its catalyzing effect speeds up the rate of reaction.

(c) Name some reducing agents and write the tests for reducing agents.
Answer:
Some examples of reducing agents are as follows :
1. Solids : Carbon, metals like zinc, aluminium, copper and sodium, stannous chloride, glucose etc.
2. Liquids : Hydrogen peroxide, hydrogen iodide, hydrogen bromide etc.
3. Gases : Hydrogen sulphide, carbon monoxide etc.

Reducing agents generally respond to the following tests :
1. They give out brown fumes of nitrogen dioxide when Warmed with nitric acid.
2. They change black copper (II) oxide on heating to a red copper metal.
3. They decolourise the pink colour of dilute potassium permanganate solution.
4. They change the colour of acidified potassium dichromate solution from orange to green.
5. They change the light yellow colour of iron (III) salts in solution to a light green colour due to the formation of iron (II) salts.

Question 6.
(a) What is the effect of the following pollutants on living beings (one in each case) ?
(i) Fluorides
(ii) Smoke particles
(iii) Lead
(iv) Mercury compounds
(v) Smog
(vi) Nitrogen oxide
Answer:
(i) Fluorides cause destruction of vegetation and affect teeth and bones.
(ii) Smoke particles cause asthma and other lung diseases.
(iii) Lead impairs the body’s metabolic activities.
(iv) They cause diseases like Minamata commonly found in fishermen.
(v) Smog reduces visibility and induces respiratory troubles.
(vi) Nitrogen dioxide causes death of many animals.

(b) Give reason :
(i) Why the temperature of boiling water does not rise even when heat is continuously supplied to it ?
(ii) Why does the salt content in cooked vegetable remain the same, irrespective of whether the cooked food is hot or cold ?
Answer:
(i) The particles of water attract one another with inter particle forces of attraction, and these forces hold the particles together in the liquid state. The heat which we supply to water during boiling is used to overcome these forces of attraction between the particles so that they become totally free and change into a gas. This latent heat does not increase the kinetic energy of water particles, and hence, temperature does not rise during the boiling of water.
(ii) The salt mainly used for cooking purpose is common salt (NaCl) and its solubility does not change with temperature.

(c) Complete the following table which refers to the action of heat on three substances named in the first column.

Substances	Colour before heating	Colour of the residue	Name of the gas	Name of the residue
(i) Cupric carbonate	–	–	–	–
(ii) Lead nitrate	–	–	–	–
(iii) Ammonium dichromate	Orange	Nitrogen	–	–

Answer:

Substances	Colour before heating	Colour of the residue	Name of the gas	Name of the residue
(i) Cupric carbonate	Green	Black	Carbon dioxide	Copper oxide
(ii) Lead nitrate	White	Reddish yellow Light yellow	Nitrogen dioxide and oxygen	Lead oxide
(iii) Ammonium dichromate	Orange	Nitrogen	Nitrogen and water vapour	Chromium oxide

Question 7.
(a) What are the main postulates of the kinetic theory of gases ? Explain in brief.
Answer:
Kinetic theory of matter : Any substance whether solid, liquid or gas is made of tiny particles (atoms, molecules or ions) which are in constant motion. This is called the kinetic theory of matter.

Postulates of the kinetic theory of gases are :
1. Composition of matter : Matter is composed of small particles atoms, molecules and ions.

2. Inter-particle space : Particles have spaces between them. These spaces are referred to as inter particle or intermolecular spaces.

3. Inter-particle attraction : Particles attract each other with a force. This force of attraction between the particles of a given substance is called inter-particle attraction or intermolecular force. The inter-particle attraction decreases with increasing distance and vice-versa.

4. Collision of particles : Particles collide with each other and with the walls of the container in both gaseous and liquid states. The total energy of the colliding particles remains the same.

5. Motion of particles : Particles are always in a state of motion. In solids, they vibrate about their fixed mean position. Liquids and gases move randomly. Due to their motion, they possess kinetic energy.

6. Energy possessed by matter : Particles are in a state of constant motion. This random movement of molecules is due to kinetic energy.

(b) Explain the manufacture of hydrogen gas by electrolysis of water.
Answer:
Hydrogen is commercially obtained by the electrolysis of water. Water is a poor conductor of eleectricity. Thus, a less volatile acid such as sulphuric acid is added to water to make it a good conductor of electricity. This is called acidulated water.

Water dissociates on passing an electric current through acidulated water.
H₂O → H⁺ + H^–
H⁺ being positively charged moves towards the cathode (negatively charged electrode). At cathode,
H⁺ + e → H
H + H → H₂
Thus, hydrogen gas is evolved at the cathode. OH^–, being negatively charged, moves towards the anode (positively charged electrode). At anode,
OH⁺ – e^– → OH
OH + OH → H₂O + O
O + O → O₂
Oxygen is evolved at the anode.
Hence, water dissociates to give hydrogen and oxygen by passing an electric current through acidulated water.

ICSE Class 9 Chemistry Question Papers with Answers

ICSE Class 9 Chemistry Sample Question Paper 7 with Answers

Section -I
(Attempt all questions from this section)

Question 1.
(a) Fill in the blanks with the correct choice given in brackets.
(i) The gas which has an acidic nature and has greenish yellow colour is …………… [chlorine/carbon dioxide]
(ii) In periodic table when one moves from noble gas He to Rn their solubility ………….. [increases/ decreases]
(iii) The elements present in group 1, 2,3 and in group 15,16,17 react to from ……………. compounds. [electrovalent/covalent]
(iv) The formula of plaster of Paris is …………………. \(\left[\mathrm{CaSO}_{4} \cdot \frac{1}{2} \mathrm{H}_{2} \mathrm{O} / \mathrm{CaSO}_{4} .7 \mathrm{H}_{2} \mathrm{O}\right]\)
(v) The most reactive noble gas is…………………. [fluorine/iodine]
Answer:
(i) Chlorine
(ii) Increases
(iii) Electrovalent
(iv) CaSO₄. H₂O
(v) Fluorine

(b) Choose the correct answer from the options given below :
(i) Which among the following are natural sources of air pollution ?
(A) Forest fire
(B) Decaving vegetation
(C) Volcanoes
(D) All of the above
Answer:
(D) All of the above

(ii) The acidic character of the oxides of the 3rd period elements left to right:
(A) Neutral
(B) Remains same
(C) Increases
(D) Decreases
Answer:
(C) Increases

(iii) An example of a solid with a liquid is :
(A) Sugar solution
(B) Soda water
(C) Alloys
(D) Water and Alcohol
Answer:
(A) Sugar solution

(iv) In SI system volume of a gas is measured in :
(A) m³
(B) cm³
(C) dm³
(D) L
Answer:
(A) m³

(v) The volume of a gas would be reduced to zero at:
(A) 0°C
(B) 100°C
(C) -273°C
(D) +273°C
Answer:
(C) -273°C

(c) Name the gas evolved in each of the following cases :
(i) When magnesium bicarbonate is heated strongly.
(ii) When Zinc oxide is heated.
(iii) When free radical Cl of chlorofluorocarbons reacts with ozone.
(iv) When ammonium dichromate is heated.
(v) When copper (II) nitrate hexahydrate is heated.
Answer:
(i) Carbon dioxide
(ii) Carbon dioxide
(iii) Chlorine monoxide and oxygen
(iv) Water vapour and nitrogen
(v) Water vapour, nitrogen dioxide and oxygen

(d) Give reason for each of the following :
(i) Why water that contains only hydrogen carbonates of calcium and magnesium is called temporary hard water?
(ii) Why the reaction stops when magnesium, zinc and aluminium reacts with steam?
(iii) Why it is safe to prepare hydrogen from sodium and potassium amalgams?
(iv) Why the reaction between Cu (II) oxide and hydrogen is called redox reaction?
(v) Why ozone layer acts as a blanket around the earth’s surface?
Answer:
(a) (i) Water that contains only hydrogen carbonates of calcium and magnesium is called temporary hard water because its hardness can be removed just by boiling.
\(\mathrm{Ca}\left(\mathrm{HCO}_{3}\right)_{2} \stackrel{\text { Boil }}{\longrightarrow} \mathrm{CaCO}_{3}+\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2}\)

(ii) When metals like magnesium, aluminium and zinc reacts with steam the reaction stops after some time. This is because the oxides of these metals stick to the surfaces of the respective metals and thus do not allow steam to come into contact of the metal.

(iii) Alloy of sodium with mercury which is also known as sodium amalgam and potassium amalgam react smoothly with water. This is because hydrogen is safe to prepare from these metals.

(iv) CuO + H₂ → Cu + H₂O is the reaction in which copper II oxide is reduced to copper by hydrogen and the oxidation of reducing agent, hydrogen to water takes place by the oxidizing agent copper II oxide. Thus, the net reaction is called redox reaction.

(v) The ozone layer acts as a blanket in the atmosphere above 16 km from the earth’s surface. Ozone absorbs the harmful ultra-violet rays coming from the sun and thus prevents them from reaching the earth. Thus, it protects life on earth from harmful effects of UV rays.

(e) Answer the following questions :
(i) Write down the two uses of hydrogen.
(ii) What do you mean by empirical formula mass and give the empirical formula of hydrogen peroxide?
(iii) What does a balanced chemical equation convey?
(iv) Write a chemical reaction in which the product thus obtained is by mixing the reactants.
(v) Write the properties of electrovalent compounds.
Answer:
(i) Use of hydrogen are as follows :
1. Hydrogen has high heat of combustion and it is used as a fuel in the form of coal gas, water gas and liquid hydrogen.
2. Atomic hydrogen torch creates high temperature (2800°C) which is used for welding alloys containing metals like tungsten, manganese and chromium.
(ii) The empirical formula mass is the sum of atomic masses of various elements present in the empirical formula. For hydrogen peroxide the empirical formula is HO and its empirical mass is 1 + 16 = 17.

(iii) A balanced chemical equation tells us the following information :
1. About the actual result of the chemical change.
2. About the reactants involved and the products formed as a result of the reaction.
3. About the number of molecules of each substance taking part in the reaction.
4. About the chemical composition of the respective molecules.

(iv) In some cases a chemical reaction occurs when two substances are mixed in their solid states.
Lead nitrate and potassium iodide react to make lead iodide (yellow).
e.g. Pb(NO₃)₂(s) + 2KI(s) 2KNO₃(s) + Pbl₂(s)

(v) Properties of electrovalent compounds are :
1. They are hard, brittle crystalline solids of ions.
Examples : These have strong electrostatic force of attraction between their ions, which cannot be separated easily.
2. They are non-volatile, with high boiling and melting points.
Example: There exists a strong force of attraction between the oppositely charged ions, so a large amount of energy is required to break the strong bonding force between ions.

(f) (i) Write down the properties of covalent compounds.
(ii) What is octet theory of valency and who put forward it?
(iii) What are transuranium elements ?
Answer:
Properties of covalent compounds are :
1. Covalent compounds are made up of molecules and they are either gases or liquids or soft solids because they have weak forces of attraction between their molecules.

2. These compounds are volatile, with low boiling point and low melting points, because they have weak forces of attraction between the binding molecules and hence less energy is required to break the force of bonding.

3. They are non-conductors of electricity in solid, molten or aqueous state. This is because there is absence of free ions and free electrons that are responsible to carry electric charge.

Octet theory of valency says that rare gases have a stable electronic configuration. The atoms of all elements other than the inert gases combine because they have incomplete valence shells and tend to attain a stable configuration. Octet theory of valency is also known as electronic theory of valency. This theory was given by Kossel and Lewis in 1916.

(iii) The elements beyond uranium, U in the seventh period are called transuranium elements. These elements do not occur naturally. They all have been prepared artificially.

(g) Answer the following questions given below.
(i) 1. What do you mean by covalency of an atom ?
2. When covalent compounds are said to be polar ?
Answer:
1. The covalency of an atom is the number of its electrons taking part in the formation of shared pairs. The covalency of hydrogen is 1, oxygen is 2, nitrogen is 3 and carbon is 4 as 1 electron of hydrogen, 2 electrons of oxygen and 3 of nitrogen and 4 of carbon take part in the formation of shared pairs.

2. The covalent compounds are said to be polar when the shared pair of electrons are not at equal distance between the two atoms. This results in the development of fractional positive and negative charges on them and they ionize in water.

(ii) 1. Give reason why covalent compounds have low boiling and melting points ?
2. Why electrovalent compounds do not conduct electricity in the solid state ?
3. How protons are discovered ?
Answer:
1. Covalent compounds have weak forces of attraction between the binding molecules, thus less energy is required to break the force of bonding.

2. Electrovalent compounds do not conduct electricity in the solid state because they are good conductors of electricity in the fused of aqueous state. The electrostatic forces of attraction between ions in the solid state are very strong, these forces weaken in the fused or in solution state. Hence ions become mobile.

3. Atoms are found to be electrically neutral, so they must contain, in addition, particles that are positively charged, such that the total negative charge of the electrons is equal to the total positive charge, This realisation lead, to the discovery of positively charged subatomic particles called protons.

(h) Match Column A with Column B.

Column A	Column B
(i) Inner transition elements	(A) KBr
(ii) Proton was discovered by	(B) Aluminuim
(iii) Calcium is more reactive than	(C) Radon
(iv) Lead is more reactive than	(D) Block elements
(v) Electrovalent compound	(E) Goldstein

Answer:
(i) (D)
(ii) (E)
(iii) (B)
(iv) (C)
(v) (A)

Section – II
(Attempt any four questions from this section)

Question 2.
(a) Give the empirical formula mass of :
(i) Benzene
(ii) Glucose
(iii) Acetylene
(iv) Acetic acid
Answer:
(i) Empirical formula mass of a compound is the sum of atomic masses of various elements present in the empirical formula. Empirical formula of :
(ii) Benzene C₆H₆ is 12 + 1 = 13
(iii) Glucose C₆H₁₂O₆ is 12 + 1 + 15 = 28
(iv) Acetylene C₂H₂ is 12 + 1 = 13
(v) Acetic acid CH₃COOH is 12 + 1 + 12 + 15 + 15 + 1 = 51

(b) Complete and balance the following chemical reactions :
(i) Mg + H₂SO₄ → …………… +………………….
(ii) M + H₂O →…………….. +…………….. (M is any metal)
(iii) ………….. + 2H₂O → 2NaOH + ………………
Answer:
(i) Mg + H₂SO₄ → MgSO, + H₂
(ii) 2M + 2H₂O → 2MOH + H₂
(iii) 2Na + 2H₂O → 2NaOH + H₂

(c) What is neutralization reaction and write down the uses of neutralization as a chemical process ?
Answer:
(c) The reaction between an acid and a base that form salt and water only is referred to as neutralization reaction. Uses of neutralization are as follows :
1. If a bee stings us, then the pain which we feeln is due to formic acid which enters the skin. Slaked lime and baking soda, both of which are bases help us from relieving its pain.
2. Ammonia solution helps in neutralization from acid which is accidentally spilled onto our clothes or on our body.
3. During fanning slaked lime is used to neutralize the acidity of the soil, as acidified soil is unfit for growing certain crops.

Question 3.
(a) Explain the process of preparation of hydrogen from sodium.
Answer:
(a) Sodium is a reactive metal and it reacts with cold water forming its corresponding hydroxide and evolving hydrogen. This reaction is exothermic.
1. Sodium floats on water : density 0.097 g/cc; point 97°C.
2. It melts, forming a silverly globule, which darts about on the surface of the water.
3. Reaction : 2NaOH + 2H₂O → 2NaOH + H₂
The above reaction is less exothermic as compared to preparation of hydrogen from potassium.
4. It catches fire and bums with a golden yellow flame.
5. Bubbles of hydrogen are produced and the solution formed is colourless, soapy, slightly warm and alkaline.

(b) (i) What is occlusion?
(ii) What do you mean by liquefaction ?
Answer:
(i) When adsorption of gases occurs on the surface of metals this is called occlusion. For example, one volume of finely divided palladium takes up 900 volumes of hydrogen at room temperature. This phenomenon is called the occlusion of adsorption.

(ii) When a substance, that is a gas in normal condition, changes to a liquid state under special conditions is called liquefaction.

(c) Write down the difference between oxidation and reduction.
Answer:

Oxidation	Reduction
Addition of oxygen.	Removal of oxygen.
Removal of hydrogen.	Addition of hydrogen.
Addition of electronegative atom or ion.	Removal of electronegative atom or ion.
Increase in positive valency.	Decrease in positive valency.
Loss of electrons.	Gain of electrons.
Decrease in negative valency.	Increase in negative valency.

Question 4.
(a) What do you mean by percentage composition ? Calculate the percentage of hydrogen in water.
Answer:
(a) Percentage composition of a compound, is the percentage by weight of each element present in it.
Percentage of an element in a compound
\(=\frac{\text { Total weight of the element in one molecule }}{\text { Gram molecular weight of the compound }} \times 100\)
Atomic mass of H is 1 and that of O is 16.
Relative molecular mass of water = 1 x 2 + 16 = 18
Since 18 g of water contains 2 g of hydrogen
Therefore 100 g of water contains =\( \frac{2}{18}\) x 100 = 11.11 g of hydrogen

(b) Write down the limitations of a chemical reaction.
Answer:
A chemical reaction does not tell us :
1. The physical state of the reactants and the products, i.e., whether the substances are solid, liquid or gas.
2. The time taken for the completion of the reaction.
3. Whether heat is given out or absorbed during the reaction.
4. The respective concentrations of the reactants and the products.
5. The rate at which the reaction proceeds.
6. Whether the reaction is reversible or irreversible.

(c) Define the following terms.
(i) Element and compound.
(ii) Atomicity and octatomic molecule.
(iii) Symbols and write the symbol for arsenic and iron.
(iv) Significance of molecular formula.
Answer:
(i) An element is a simple and pure form of matter which cannot be decomposed into simpler substances. Whereas when atoms or molecules of different elements combine they form the molecule of a compound.

(ii) The number of atoms in a molecule of an element is called its atomicity. Octatomic elements have eight atoms in their molecules g., sulphur (S₈).

(iii) A symbol is the short form that stands for the atom of a specific element or the abbreviations used for the names of elements. The symbol for arsenic is Ar and that of iron is Fe.

(iv) Molecular formula has the following significance :

1. It represents both the molecule and the molecular mass of the compound.
2. It represents the ratio of the respective masses of the elements present in the compound.

Question 5.
(a) Define
(i) Pollution
(ii) Pollutant
(iii) Air pollution.
Answer:
(i) The word pollution is derived from the Latin word “pollutes”, which means “made dirty”. Pollution is created by harmful substances generally produced by human beings.

(ii) The substance that causes pollution is known as Pollutant. Thses substances contaminate and degrade earth’s environment and have an adverse affect not only on human life but as well as on plants and animals.

(iii) Air pollution means degradation of air quality due to concentration of harmful contaminants that affects human, plant and animal lives.

(b) (i) What is Smog ?
(ii) What is the main cause of acid rain ?
(iii) Write various gaseous pollutants and their effects.
Answer:
(i) A pollutant, which is a combination of oxides of nitrogen and sulphur and of partially oxidized hydrocarbons and their derivatives produced by industries and automobiles form a dark, thick, dust and soot laden fog and is known as Smog.
(ii) The main cause of acid rain is the presence of air pollutants, like sulphur dioxide and nitrogen oxides.

(c) Write various gaseous pollutants and their effects.
Answer:
Gaseous pollutants are the main cause of air pollution. Various gaseous pollutants and their side effects are as follows :
1. Sulphur dioxide affects yields of crops and causes damage to lungs.
2. Hydrogen sulphide gas reduces growth of crops and causes irritation to human eyes.
3. Fluorides cause destruction of vegetation and affects teeth and bones.
4. Nitrogen oxides cause death of many plants and are supposed to cause cancer.
5. Carbon monoxide prevents haemoglobin from carrying oxygen to different parts of the body.
6. Tobacco smoke causes lung cancer.
7. Lead, which enters air from motor vehicles using tetraethyl lead, impairs the body’s metabolic activities.
8. Cotton dust produces lung fibrosis and smoke particles cause asthma and other lung diseases.

Question 6.
(a) What are oxidizing and reducing agents and state which of the following are oxidized or reduced ?

Answer:
(a) Oxidising agent : The substance which loses oxygen or an electronegative radical is called an oxidising agent. The substance which gains hydrogen or an electropositive radical is also called as an oxidising agent. They get reduced in a reaction.

Reducing agent : The substance which loses hydrogen or an electronegative radical is called reducing agent. The substance which gains oxygen or an electronegative radical is also called as reducing agent. They get oxidized in a reaction.
(i) Oxidized
(ii) Oxidized
(iii) Reduced
(iv) Oxidized
(v) Oxidized.

(b) Answer the following :
(i) Why physical properties of isotopes are different ?
(ii) Why is steam more dangerous than boiling water ?
Answer:
(i) Physical properties depend on atomic mass, and isotopes have different mass number, i.e., they have different number of neutrons. So, isotopes have different physical properties.

(ii) Steam is more dangerous than boiling water because, particles in steam (water vapour) at 373 K (1000°C) have more energy than water at the same temperature. This is because particles in steam have absorbed extra energy in the form of latent heat of vapourization. Thus, steam is more dangerous than water vapour.

(c) Give the balanced chemical equations for the following :
(i) Electrolysis of lead bromide.
(ii) Electrolysis of water.
(iii) Decomposition of silver bromide.
Answer:

Question 7.
(i) Identify the element present in the following groups and periods :
1. Group 1, Period 5
2. Group 11, Period 4
3. Group 16, Period 2
4. Group 17, Period 3
5. Group 18, Period 4
6. Group 2, Period 3

(ii) Elements A, B, C and D have atomic numbers 8, 9, 11 and 12, respectively.
1. Write the electronic configurations of the elements.
2. Choose the electropositive and electronegative elements from the above elements.
Answer:
(a) (i) 1. Rubidium, 2. Copper, 3. Oxygen, 4. Chlorine, 5. Krypton, 6. Magnesium
(ii) 1.

Elements	Atomic Number		Electronic Configuration
		K	L	M
A	8	2	6	–
B	9	2	8	–
C	11	2	8	1
D	12	2	8	2

2. Electropositive elements are C and D.
Electronegative elements are A and B.

(b) Water is purified for scientific purposes by distillation. Describe the process.
Answer:
Water is purified by following way through distillation.
1. For scientific purposes, pure water is obtained by repeated distillation of ordinary water.

2. The process of converting liquid into vapour by heating and the subsequent condensation of the vapour back into a liquid is called distillation.

3. This method is used to remove impurities from water. The water so obtained is called distilled water. It is the purest form of water. It is used for scientific purposes for experiments in the laboratory, for preparing solutions for medical purposes, for car batteries etc.

4. Impure water is kept in the distilling flask and then boiled. Water turns into steam and passes through the Liebig condenser. Steam on coming in contact with the cooler parts of the condenser condenses water and gets collected as distillate (distilled water) in the receiver.

5. The dissolved impurities remain in the flask.

(c) Give the structure and molecular mass of water molecule.
Answer:

and molecular mass of water (H₂O) = 1 x 2 +16 = 2 +16 = 18 amu

ICSE Class 9 Chemistry Question Papers with Answers

 

ICSE Class 9 Chemistry Sample Question Paper 6 with Answers

Section-I
(Attempt all questions from this section)

Question 1.
(a) Fill in the blanks with the correct choice given in brackets.
(i) The chemical change involving iron and hydrochloric acid illustrates a …………………… reaction. [change of state/change of colour]
(ii) In the type of reaction called………………….. two compounds exchange their positive and negative redicals. [displacement/decomposition]
(iii) The composition of air water is………………………. [33%/35%]
(iv) Distilled water and boiled water have………………….. [no/sweet]
(v) ……. is the solution in which the amount of solute is rather small compared to the mass of the solvent.  [Dilute / Concentrated]
Answer:
(i) Change of state
(ii) Displacement
(iii) 33%
(iv) No
(v) Dilute

(b) Choose the correct answer from the options given below :
(i) Which molecules have four atoms in their molecules ?
(A) Tetratomic
(B) Diatomic
(C) Monoatomic
(D) Triatomic
Answer:
(A) Tetratomic

(ii) What is the significance of a symbol ?
(A) Name of the element
(B) One atom of the element
(C) A definite mass of the element
(D) All of the above
Answer:
(D) All of the above

(iii) What is the other name for Relative Atomic Mass (RAM) ?
(A) Molecular mass
(B) Molecular weight
(C) Atomic weight
(D) None of the above
Answer:
(C) Atomic weight

(iv) Choose hygroscopic substances from the substances given below :
(A) H₂SO₄
(B) P₂O_s
(C) CaO
(D) All of the above
Answer:
(D) All of the above

(v) The gas which is brown is brown in colour and has irritating odour is :
(A) Sulphur dioxide
(B) Hydrogen chloride
(C) Nitrogen dioxide
(D) Ammonia
Answer:
(C) Nitrogen dioxide

(c) Name the gas evolved in each of the following cases :
(i) When sodium hydrogen carbonate is heated strongly.
(ii) When copper sulphate solution is heated.
(iii) Glucose when oxidized gives.
(iv) When nitric oxide reacts with ozone.
(v) When ammonium chloride is cooled down.
Answer:
(i) Carbon dioxide
(ii) Sulphur dioxide and oxygen
(iii) Carbon dioxide
(iv) Nitrogen dioxide and nitrogen trioxide
(v) A basic gas (NH₃) and an acidic gas (HCl)

(d) Give reason for each of the following :
(i) Why synthetic detergents are used instead of soap for washing purposes ?
(ii) Why the electronic configuration of calcium is 2, 8, 8, 2 and not 2, 8, 10 ?
(iii) Why hydrogen occupies a position in the activity or reactivity series of metals ?
(iv) Why gases have low density ?
(v) Why the compound formed by covalent bond is called covalent compound ?
Answer:
(i) Soap is chemically sodium salt of stearic acid, when clothes are washed with soap, the calcium and magnesium ions of the hard water combines with negative ions of the soap to form insoluble calcium and magnesium salts. Detergents on the other hand work well in hard water also as they do not form any insoluble salts.

(ii) According to the rule of electronic configuration, the outermost shell of an atom can not accommodate more than 8 electrons, even if it has the capacity to accommodate more electrons. This is due to the fact that the elements become stable only after acquiring 8 electrons in the outermost shell. That is why the electronic configuration of calcium is 2, 8, 8, 2 and not 2, 8, 10.

(iii) In reactivity series potassium being the most reactive is placed at the top of the series and Gold being the least reactive is placed at the bottom of the series and hydrogen, though is a non-metal it is included in the list because it can form positive ion. It would occupy a position based on formation of its positive ions.

(iv) The number of molecules per unit volume in a gas is very small as compared to solids and liquids. Gases have large inter-molecular space between their molecules. Therefore gases have very low density.

(v) The chemical bond that is formed between two combining atoms by mutual sharing of one or more pairs of electrons is called a covalent bond and the compound formed due to this bond is called a covalent compound.

(e) Answer the following questions :
(i) Why concentrated sulphuric acid being a good drying agent is not used to dry hydrogen ?
(ii) What is a promoter ?
(iii) What is a radical and write down its types ?
(iv) Write a short note on freezing point of water.
(v) What are the characteristics of a true solution ?
Answer:
(i) Cone. Sulphuric acid is a good drying agent but is not used to dry hydrogen as it reacts with hydrogen.
H₂SO₄ + H₂ → 2H₂O + SO₂

(ii) Substance that influences the rate of a chemical reaction by improving the efficiency of the catalyst is called a promoter. For example, in the manufacture of ammonia, iron acts as a catalyst and molybdenum acts as a promoter. Molybdenum increases the efficiency of the catalyst iron.

(iii) A radical is an atom or a group of atoms of the same or of different elements that behaves as a single unit with a positive or a negative charge. There are two types of radicals, first is simple g., Na⁺, second is compound radical e.g., (SO₄^2-).

(iv) Pure water freezes at 0°C under normal pressure e., one atmosphere. The freezing point of water decreases with increase in pressure. The freezing point of water also decreases due to the presence of dissolved impurities in it.

(v) Characteristics of a true solution are :
(1) It is a homogeneous mixture.
(2) The solute particles are very small about 10^-10
(3) It is clear and transparent.
(4) It does not scatter light.

(f) (i) Write down the difference between drying agent and dehydrating agent.
(ii) Write two methods by which gases are dried.
(iii) What do you observe when iodine crystals are heated in a test tube ?
Answer:
(i) (i) Drying agent are substances that can readily absorb moisture from other substances and Dehydrating substances are substances that can remove even the chemically combined water molecules from compounds.

Difference between Drying agent and Dehydrating agent :

Drying agent	Dehydrating agent
They remove moisture from other ‘          substances.	They remove chemically elements of water in the ratio 2:1 from a compound.
They are used to dry gases like chlorine, sulphur dioxide, hydrogen chloride etc. and used in desiccators to keep substances dry.	They prepare substances like carbon mon­oxide, sugar charcoal.
They represent physical change, e.g. Phosphorus pentaoxide, fused calcium chloride.	They represent chemical change, e.g., cone, sulphuric acid.

(ii) Two methods to dry gases are :
1. Passing them through a drying tower or a U-tube containing anhydrous sodium sulphate.
2. Passing the gases through cone, sulphuric acid, because cone, sulphuric acid has strong affinity for water, so it easily extracts water from many substances. Cone, sulphuric acid is used to dry gases which are acidic in nature like hydrogen chloride gas.

(iii) When Iodine Crystals are heated in a test tube, the Van der Waals forces are easily overcome and the molecule breaks into gas phase. They sublime and form a purple coloured dense vapours.

(g) (i)
1. Explain the process of exothermic reaction that takes place in our body.
2. What are insoluble, sparingly soluble and soluble substances ?
Answer:
1. Our body needs energy to make possible the reactions that takes place in our cells. These reactions allow us to carry our everyday activities. We need energy to stay alive and we get this energy from food. During digestion, food is broken down into simpler substances and energy is released in this process. For example : The carbohydrates in rice, potatoes and bread are broken down to form glucose.

The combustion of glucose with oxygen in the cells of the body provides energy :
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
The reaction is exothermic and it is known by a special name respiration.

2. A substance that has negligible solubility is called insoluble. For example, silver chloride which has 0.000015 g as its solubility. A substance that has more than negligible but less than high solubility is called sparingly soluble. For example, calcium hydroxide which has 0.17 g as its solubility.
A substance having high solubility such as sodium chloride is simply called soluble.
A solution that can hold more solute than it can theoretically do at room temperature is a supersaturated solution.
Iodine crystals Carbon dioxide

(ii) 1. Define the term supersaturated solution.
2. Name the white cryrtalline’substance which sublimes on heating.
3. Name the gas which turns lime water milky but has no effect on potassium dichromate paper.
Answer:
1. A solution that can hold more solute than it can theoretically do at room temperature is a supersaturated solution.
2. Iodine crystals
3. Carbon dioxide

(h) Match Column A with Column B.

Column A	Column B
(i) Removal of temporary hardness	(A) Lewis symbol
(ii) Metals	(B) Clark’s process
(iii) Electron dot symbol	(C) Are good oxidising agents
(iv) Hydrogen gas is discovered by	(D) Are good reducing agents
(v) Non-metals	(E) Henry Cavendish

Answer:
(i) (B)
(ii) (D)
(iii) (A)
(iv) (E)
(v) (C)

Section – II
(Attempt any four questions from this section)

Question 2.
(a) Write down the factors affecting solubility of a solid and give examples.
Answer:
The rate of dissolution or rate of solubility of a solid in a liquid depends on the following factors :

1. Size of solute particles : The smaller the size of the solute particles, the greater is its total surface area exposed to the solvent. Therefore, the greater is the solubility of that solute.

2. Stirring : This brings more of the solvent in contact with the solute and thus increases the rate of formation of solution.

3. Temperature : The solubility of a gas in a liquid always decreases with rise in temperature. But the solubility of most solids in water usually increases with rise in temperature.

For example : The solubility of potassium nitrate in water at 20°C is 31.6 grams, whereas its solubility at 60°C is 6.9 grams. All these factors affect solubility because in the process of dissolution, the particles of solute merely occupy the spaces between the particles of solvent without undergoing any chemical change.

(b) Explain the following :
(i) Crystals
(ii) Crystallisation
(iii) Name few methods by which crystals can be prepared in laboratory.
Answer:
(i) A crystal is a homogeneous solid of definite geometrical shape. It has symmetrically arranged smooth plane surfaces which meet forming the sharp edges.

(ii) It is process by which crystals of a substance are obtained by cooling a hot saturated solution. All crystals of pure compound are of similar shape, but those of different compounds may be of different shapes. Some shape in which crystals exists are : cubic (NaCl), octahedral (FeSO₄) etc.

(iii) Crystals can be prepared by the following methods.
1. by cooling a hot saturated solution.
2. by slowly evaporating a saturated solution.
3. by cooling a fused mass.
4. by sublimation.

(c) (i) 12 g of saturated solution of potassium chloride at 20°C, when evapurated to dryness, leaves a solid residue of 3 g. Calculate the solubility of potassium chloride,
(ii) How will you determine the water of crystallisation ? Explain the procedure.
Answer:
(i) Weight of water in solution = 12g-3g = 9g
9 g of H₂O dissolves 3 g of solid.
Therefore 100 g of water will dissolve (3/9) x 100 = 33.3 g
Solubility of KCl in H₂O at 20°C is 33.3 g.

(ii) Take a known weight of crystals in a China dish and heat it above 100°C. When the weight of the residue becomes constant, stop heating.
Wt. of crystals at room temperature = a g
Wt. of crystals after heating at 101°C = bg.
Wt. of water = (a -b) g
Now a g of crystals contain water = (a -b) g
Therefore % of water of crystallisation = [(a – b) /a] x 100

Question 3.
(a) How will you incorporate the following information into an equation ?
(i) Presence of catalyst.
(ii) Temperature and pressure conditions.
(iii) Evolution of a gas.
(iv) Formation of
(v) Evolution of heat.
(vi) Physical state of the reactants and products.
Answer:
(i) Catalyst is written above the arrow.
(ii) The temperature and pressure conditions are written above or below the arrow.
(iii) Evolution of gas is depicted by an upward arrow (↑).
(iv) Formation of precipitate is depicted by a downward arrow (↓).
(v) Evolution of heat is represented by writing ‘Δ’ sign ‘+ Heat’ on the product side.
(vi) Physical state of the reactants and products are represented by writing (s), (1) and (g) adjacent to the reactants and products which represents solid, liquid and gas respectively.

(b) Answer the following questions.
(i) Name the process in which water gas is used for the manufacture of hydrogen.
(ii) Give the balanced chemical equation for the large-scale preparation of hydrogen from water gas.
(iii) How are carbon dioxide and carbon monoxide removed from hydrogen produced ?
Answer:
(i) Bosch process in which water gas is used for the manufacture of hydrogen.
(ii)
(iii) Hydrogen obtained by this process contains impurities of carbon monoxide in traces and carbon dioxide. Carbon monoxide can be removed by passing it through ammonical cuprous solution. Carbon dioxide can be removed by passing it through cold water under pressure.

(c) Write the electronic configuration, number of valence electrons and classify the following as metals, non-metals and inert gases.

Answer:

Question 4.
(a) Select metals from the given list and match them with the statements given below. Lithium, Sodium, Gold, Aluminium, Potassium.
(i) Reacts vigorously with cold water to liberate hydrogen.
(ii) Bums with a golden yellow flame.
(iii) Bums with lilac flame.
(iv) Dissolves in aqua regia.
(v) Reacts with both acids and alkalis to liberate hydrogen.
Answer:
(i) Potassium reacts vigorously with cold water to liberate hydrogen.
(ii) Sodium bums with a golden yellow flame.
(iii) Lithium bums with lilac flame.
(iv) Gold dissolves in aqua regia.
(v) Aluminium reacts with both acids and alkalis to liberate hydrogen.

(b) (i) Write the chemical formula of the sulphates of aluminium, ammonium and zinc.
(ii) Why does the salt content in cooked vegetable remain the same, irrespective of whether the cooked food is hot or cold ?
(iii) Describe the discovery of anode rays with the help of a labelled diagram.
Answer:
(i) Valencies of aluminium, ammonium and zinc are 3, 1 and 2 respectively. The valency of sulphate is 2.
Hence chemical formulae of the sulphates of aluminium, ammonium and zinc are
Al₂(SO₄)₃, (NH₄)₂SO₄ and ZnSO₄.
(ii) The salt mainly used for cooking purpose is common salt (NaCl) and its solubility does not change with temperature.

(c) Describe the discovery of anode rays with the help of a labelled diagram.
Answer:
Discovery of anode rays :
1. The German scientist E. Goldstein modified the discharge tube with a perforated cathode and passed an electric current through it.
2. He found that certain rays travel in the direction opposite to that of the cathode rays. There rays are called anode rays.

3. When an electric field is applied, these rays deflected towards the negatively charged plate (cathode). Thus, Goldstein concluded that an atom contains positively charged particles along with the electrons.
4. These positively charged particles were named protons by the British scientist Ernest Rutherford.
5. The deflection of anode rays towards the cathode depends on the type of gases taken inside the tube. Heavier the gas, lower is the deflection.

Question 5.
(a) Write a note on chloro-fluorocarbons and how they are decomposed ?
(b) Write the main causes of acid rain.
(c) Explain the mechanism of global warming.
Answer:
(a) Chloro-fluorocarbons enter the atmosphere because of their excessive use in solvents, aerosol sprays, propellants and blowing agents for plastic foam. Chlorofluorocarbons are decomposed by ultraviolet rays to highly reactive chlorine which is produced in the atomic form.

The free redical [Cl] reacts with ozone to form chlorine monoxide.

This causes depletion of the ozone layer. Chlorine monoxide then reacts with atomic oxygen to produce more chlorine free radicals.

Again this free radical destroys ozone, and the process continues, depleting the ozone layer.

Again this free radical destroys ozone, and the process continues, depleting the ozone layer.

(b) Causes of acid rain are :
The formation of mineral acids such as carbonic acid, nitric acid and sulphuric acid is the main cause of acid rain.
Formation of nitric acid and nitrous acid :
1. Nitrogen and oxygen combine in the presence of thunder and lightning to form nitrogen
2. Nitrogen oxide then gets oxidised in the atmosphere to form nitrogen dioxide.
3. Nitrogen dioxide combines with water to form a mixture of nitrous acid and nitric acid.

They are also produced by internal combustion engines (automobile engines). Formation of sulphuric acid and sulphurous acid :

1. Impurities in Coal : Coal used in power plants contains up to 4% sulphur. On combustion, it forms pollutant sulphur dioxide (i.e., oxides of sulphur).
S + O₂ → SO₂ (Sulphur dioxide)

2. Sulphur dioxide reacts with water vapour to form sulphurous acid.
SO₂ + H₂O → H₂SO₃ (Sulphurous acid)

3. Sulphur dioxide can also be oxidized to sulphur trioxide.
2SO₂ + O₂→ 2SO₃ (Sulphur trioxide)

Sulphur trioxide reacts with water vapour to form sulphuric acid.

(c) Carbon dioxide has the capacity to absorb heat radiations emitted from earth surface in the form of infra red radiations (which have longer wave length and have a heating effect) and thus increases temperature. The increase in global temperature (global warm¬ing) is mainly due to carbon dioxide concentration and is called Greenhouse effect.

The green house effect was first described by the French mathematician J. Fourier in 1827. Due to heavy industrialization and transportation, carbon dioxide concentration is increasing day by day in the atmosphere. Besides carbon dioxide, some other gases associated with green house effect are methane, oxides of nitrogen and ozone. These are called greenhouse gases. Carbon dioxide is the most important green house gas.

These gases never let the radiations escape from the earth and hence the surface temperature of the earth increases and this is called Global warming. Hence, the greenhouse effect leads to global warming.

Question 6.
(a) Why does the temperature of boiling water not rise even when heat is continuously supplied to it ?
Answer:
The particles of water attract one another with inter particle forces of attraction, and these forces hold the particles together in the liquid state. The heat which we supply to water during boiling is used to overcome these forces of attraction between the particles so that they become totally free and change into a gas. This latent heat does not increase the kinetic energy of water particles, and hence, temperature does not rise during the boiling of water.

(b) What is a true solution ? Write down its characteristics.
Answer:
A solution in which the size of the solute particles is about 10^-10 m is called a true solution.
Characteristics of a true solution are as follows :

1. It is a homogeneous mixture.
2. It is clear and transparent.
3. It does not scatter light.
4. Its composition cannot be separated by filtration.
5. The solute particles in a solution does not settle down.

(c) Write down the process of preparation of supersaturated solution, and also write how you can bring down the temperature of supersaturated solution.
Answer:
A saturated solution of a solute, say potassium nitrate is prepared in slightly warm water. On cooling this solution, the excess nitrate does not separate out. This solution contains more solute in it than it can hold at room temperature, and therefore it is a supersaturated solution.

It is possible to bring down the temperature of a saturated solution a little without the excess solute crystallizing out if :

1. No suspended impurities, like dust particles, are present in it.
2. The solution is not distributed physically, e., it is left standing still in its container.

Question 7.
(a) What are alkaline earth metals and write down their characteristics.
Answer:
(a) The elements such as beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra) are known as alkaline earth metals, because oxides occur in the earth’s crust and their hydroxides are weak alkalies. They are placed in HA group of the periodic table.
Their main characteristics are as follows :
1. Electronic configuration :

2. Occurrence : They are reactive metals; hence they do not occur in free state.
3. Nature : They are grayish white colour and harder than the alkali metals.
4. Bonding : All the alkaline earth metal salts except beryllium are ionic compounds.
5. Action of air : They are less reactive than alkali metals.
6. Melting points and boiling points : They are comparatively low but these are higher than the alkali metals.

(b) Answer the following questions :
(i) Define group and period.
(ii) Name the elements present in Group 1 sequentially.
Answer:
(i) In the periodic table, the vertical lines are called groups and the horizontal lines are called periods.
(ii) Lithium, sodium, potassium, rubidium, caesium, francium.

(c) (i) Name the first and last element present in Group 17.
(ii) Name the first and last element of Period 2.
Answer:
(i) First element: Fluorine; Last element: Astatine
(ii) First element: Lithium; Last element: Neon

ICSE Class 9 Chemistry Question Papers with Answers

ICSE Class 9 Chemistry Sample Question Paper 5 with Answers

Section-I
(Attempt all questions from this section)

Question 1.
(a) Fill in the blanks with the correct choice given in brackets.
(i) The reaction between an acid and a base that forms slat and water only is known as ……………… [precipitation / neutralization]
(ii) Carbonates of …………. and potassium do not produce carbon dioxide on heating. [sodium/aluminium]
(iii) The reactions in which the direction of chemical change can be reversed by changing the conditions is known as …………… reaction, [reversible/irreversible]
(iv) A solution in which more of the solute can be dissolved at a given temperature is known as …………….. [unsaturated/saturated solution]
(v) ……………. is the example of hydrated substance. [Table salt/Copper sulphate pentahydrate]
Answer:
(i) Neutralization
(ii) Sodium
(iii) Reversible reaction
(iv) Unsaturated solution
(v) Copper sulphate pentahydrate

(b) Choose the correct answer from the options given below :
(i) The symbolic representation of a molecule is known as :
(A) Molecular formula
(B) Formula
(C) Chemical formula
(D) All of the above
Answer:
(D) All of the above

(ii) Elements having only one atom in their molecular are known as :
(A) Diatomic molecule
(B) Monoatomic molecule
(C) Triatomic molecule
(D) Tetratomic molecule
Answer:
(B) Monoatomic molecule

(iii) Hygroscopic substances are :
(A) Cone. Sulphuric acid
(B) Quicklime
(C) P₂O₅
(D) All of the above
Answer:
(D) All of the above

(iv) P₁V₁ = P₂V₂ is which law ?
(A) Charle’s law
(B) Boyle’s law
(C) Gas law
(D) None of the above
Answer:
(B) Boyle’s law

(v) If pressure is doubled for a fixed mass of a gas, its volume will become
(A) 1/2 times
(B) no change
(C) 4 times
(D) 2 times
Answer:
(D) 2 times

(c) Name the reducing agent in the following reactions :
(i) Fe₂O₃ + 3CO → 2Fe + 3CO₂
(ii) CuO + H₂ → Cu + H₂O
(iii) ZnO + C → Zn + CO
(iv) 3CuO + 2NH₃ → 3Cu + N₂ + 3H₂O
(v) PbO + C → Pb + C
Answer:
(i) Carbon monoxide
(ii) Hydrogen
(iii) Carbon
(iv) Ammonia
(v) Carbon

(d) Give a reason for each of the following :
(i) Metals form positive ions.
(ii) Why should an equation be balanced ?
(iii) Why deliquescence is minimized during dry conditions ?
(iv) Why quick lime acts as a drying agent ?
(v) Noble gases do not combine with other elements to form molecules.
Answer:
(i) In order to attain stable state metals lose their valence electrons and form positive ions.
(ii) An equation must be balanced in order to comply with the “law of conservation of matter” which states that matter is neither created nor destroyed in the course of a chemical reaction. An unbalanced equation would imply that atoms have been created or destroyed.
(iii) Deliquescence occurs when vapour pressure inside the crystals is very low compared to vapour pressure in the atmospheric air. Thus deliquescence is minimized during dry conditions.
(iv) Quicklime being basic in nature is suitable for drying NH₃, a basic gas. Basic gas will not react with base.
(v) Noble gases do not combine with other elements to form molecules because they have 8 electrons in their outermost orbits, except helium which has 2.

(e) Answer the following questions :
(i) Write a chemical reaction which proceeds with the absorption of sound energy.
(ii) Write a chemical reaction depicting change of state.
(iii) Write two uses of neutralization.
(iv) Write the importance of dissolved salts in water.
(v) What is a solution?
Answer:
(i) Acetylene breaks up into carbon and hydrogen by absorbing sound energy.
\(\mathrm{C}_{2} \mathrm{H}_{2} \stackrel{(\text { sound energy })}{\longrightarrow} 2 \mathrm{C}+\mathrm{H}_{2}\)

(ii) Ammonia gas reacts with hydrogen chloride gas to produce solid ammonium chloride.
\(\mathrm{NH}_{3}(\mathrm{~g})+\mathrm{HCl}(\mathrm{g}) \rightleftharpoons \mathrm{NH}_{4} \mathrm{Cl}(\mathrm{s})\)

(iii) 1. Acid that is accidentally spilled into our clothes or body can be neutralized with ammonia solution.
2. If the soil is some what acidic, and thus unfavourable for growing of certain crops, slaked lime is added to neutralize the excess acid.

(iv) 1. They are essential for growth and development of plants.
2. They add taste to water.

(v) A solution is a homogeneous mixture of two or more components whose composition may be gradually changed by changing the relative amounts of the compounds.

(f) (i) Write the cleansing action of soaps and detergents.
(ii) Answer the following questions :

1. Name the shell denoted by A, B, C. Which shell has the least energy.
2. Name X, state the change on it.
3. The above sketch is………………… model of an atom.

(iii) What was was the basis of Mendeleev’s periodic law.
Answer:
(i) When a soap or detergent is dissolved in water, the molecules gather as clusters called micelles. The tails stick inwards and the head outwards.

In cleansing action, the hydrocarbon tail attaches itself to oily dirt. When water is stirred, the oily dirt tends to lift off from the dirty surface and dissociates into fragments. This gives an opportunity to other tails to stick to oil. The solution now contains small globules of oil surrounded by detergent molecules. The negatively charged heads present in water prevent the small globules from coming together and form aggregates. Thus, the oily dirt is removed from the object.

(ii) 1. The shell denoted by A is K, B is L and C is M. The orbit close to the nucleus has the least amount of energy.
2. X is nucleus and it has positive charge.
3. The above sketch is of Bohr’s model of an atom.
Mendeleev’s periodic law was bared on atomic masses.

(g) (i)
1. What is a balanced chemical equation ?
2. Write the partial equation method for balancing a chemical equation.
Answer:
1. It is an equation in which the total number of atoms of each element in the reactants, on the left side of the equation, is the same as the number of atoms in the products formed, on the right side of the equation.

2. Balancing can be done more easily by supposing the complex reaction to take place in steps. Write the equations for these individual steps and then add the equations. This method is known as balancing by partial equation method.

(ii) Balance the following chemical equations :
1. As₂O₃ + SnCl₂ + HCl → SnCl₄ + 2As + H₂O
2. Cu + H₂SO₄ → CuSO₄ + SO₂ + H₂O
3. Mg(s) + H₂SO₄(dil.) MgSO₄(aq) + H(g)
Answer:
1. As₂O_s + 3SnCl₂ + 6HCl → 3SnCl₄ + 2As + 3H₂O
2. Cu + 2H₂SO₄ → CuSO₄ + SO₄ + 2H₂O
3. Mg(s) + H₂SO₄(dil.) → MgSO₄(aq) + 2H(g)

(h) Match Column A with Column B.

Column A	Column B
1. Positive ions are known as 2. Photosynthesis 3. Chemical name of water 4. Negative ions are known as 5. Alloys	(A) Dihydrogen oxide (B) Cations (C) Chlorophyll (D) A solid with another solid (E) Anions

Answer:
(i) (B) (ii) (C) (iii) (A) (iv) (E) (v) (D)

Section – II
(Attempt any four questions from this section)

Question 2.
(a) Define the following terms :
(i) Valency
(ii) Cation
(iii) Symbol
Answer:
(a) (i) Valency is the number of electrons, that atom can lose, gain or share during a chemical reactions.
(ii) Cation is a positively charged ion which is formed when an atom loses one or more electrons.
(iii) A Symbol is the short form which stands for the atom of a specific elements or the abbreviations used for the names of elements.

(b) (i) What is an element ?
(ii) What are the constituents of an atom ?
(iii) Arrange in an increasing order of atomic size (Cl, I, Br).
Answer:
(i) Element is a substance which cannot be split up into two or more simple substances by usual chemical methods of applying heat, light or electric energy; for example, hydrogen, oxygen and chlorine.
(ii) Nucleus (protons, neutrons) with associated electrons; mass number and atomic number are the constituents of an atom.
(iii) Cl < Br < I

(c) What does a balanced chemical equation convey? Explain in detail.
Answer:
A chemical equation gives following information :
1. The actual result of a chemical change.
2. The substances which take part in a chemical reaction, and the substances which are formed as a result of the reaction.
3. The number of atoms of each element participating in the reaction.
4. The number of molecules of different substances taking part in the chemical reaction.
For example :     Zn + H₂SO₄ ZnSO₄ + H₂
5. Here, one molecule of zinc and one molecule of sulphuric acid react to give one molecule of zinc sulphate and one molecule of hydrogen.
6. Composition of respective molecules, for example : One molecule of sulphuric acid contains two atoms of hydrogen, one atom of sulphur and four atoms of oxygen.
7. Relative molecular masses of different substances, for example : molecular mass of following elements and compounds.
(a) Zn = 65,
(b) H₂SO₄ = (2 + 32 + 64) = 98
(c) ZnSO₄ = (65 + 32 + 64) = 161
(d) H₂ = 2
8. It tells about the volume of gaseous reactants and products.
Example :
N₂ + 3H₂  → 2NH₃
1 vol. 3 vol. 2 vol.

Question 3.
(a) Write a short note on occurrence of hydrogen.
(b) Explain why in the laboratory, hydrogen is not prepared by the reaction of lead with dilute sulphuric acid or dilute hydrochloric acid.
(c) Write general trends of the Modem periodic table.
Answer:
(a) Free State : In free state, hydrogen is found in traces in the earth’s crust and atmosphere. Volcanic gases contain 0.025% of it, the earth’s crust 0.98%, the earth’s atmosphere 0.01% and the atmosphere of the sun and the stars contain 1.1% hydrogen.

Combined State :
1. Plant and animal tissues are made up of compounds of hydrogen with carbon, oxygen and nitrogen.
2. Hydrogen is the characteristics constituent of acids, alkalis, hydrogen and proteins. In addition to these, sugar, starch, petroleum products, proteins, carbohydrates and also fats contain hydrogen.

(b) In the laboratory, hydrogen is not prepared by the reaction of lead with dilute sulphuric acid or dilute hydrochloric acid because it forms insoluble lead sulphate and insoluble lead chloride, respectively, which prevents the reaction of metals with acids.

(c) General trends of the Modem periodic table :

Groups :
1. Numbers of shells and valence electrons : Number of shells increases arithmetically and number of valence electrons remains equal to the number of the group to which the element belongs. Also, number of electron shells in a given element to the number of period to which it belongs.

2. Valency : Valency of an element equals the number of electrons present in its valence shell. Valency for all the elements in a group is same.

3. Properties of Elements : Elements in a given group possess similar electronic configuration because the number of electrons in their respective outermost shells is the same, hence they have similar physical and chemical properties.

4. Atomic Size : As one moves down a group, size of atoms of successive elements increases.

5. Metallic character : Metallic character increases as one moves down a group.

Periods :
1. Number of shells : On moving from left to right in a given period, number of shells remains the same.
2. Number of electrons in valence shell : In a given period, number of electrons in valence shell increases from left to right.
3. Valency : Valency of elements, with respect to hydrogen, increases arithmetically from 1 to 4 and
back to 1.
4. Size of Atoms : Size of atoms decreases when moving left to right in a period.
5. Metallic character : On moving from left to right in a period metallic character gradually decreases i.e. changes from metallic to non-metallic.

Question 4.
(a) Which of the lettered elements is :

(i) An inert gas
(ii) A transition element
(iii) An alkali metal
(iv) An alkaline earth metal
(v) A halogen
(vi) Forms a diatomic molecule
Answer:
(i) C,I
(ii) F,G
(iii) D
(iv) A
(v) H
(vi) B and H

(b) How will you incorporate the following information into an equation ?
(i) Temperature and pressure conditions
(ii) Formation of precipitate
(iii) Evolution of a gas
Answer:
(i) The temperature and pressure conditions are written above or below the arrow.
(ii) Formation of a precipitate is depicted by a downward arrow
(iii) Evolution of a gas is depicted by an upward arrow.

(c) Convert the following temperature (in °C) to the Kelvin scale.
(a) – 100°C
(ii) 273°C
(iii) 20°C
(iv) 5°C
(v) 300°C
Answer:
(i) -100°C = – 100 + 273 = 173 K
(ii) 273°C = 273 + 273 = 546 K
(iii) 20°C – 20 + 273 = 293 K
(iv) 5°C = 5 + 273 = 278 K
(v) 300°C = 300 + 273 = 573 K

Question 5.
(a) Explain what you understand from the following diagram :

Answer:
1. When a soild changes into a liquid, it absorbs heat equal to the latent heat of fusion. When a liquid changes into a solid, it loses heat equal to the latent heat of solidification.
2. When a liquid changes into a gas, it absorbs heat equal to the latent heat of vapourization. When a gas condenses into a liquid, it loses heat equal to the latent heat of condensation.

(b) (i) Why does the temperature of boiling water not rise even when heat is continuously supplied to it ?
(ii) Write the process of removal of temporary hardness by boiling water.
Answer:
(i) The particles of water attract one another with inter particle forces of attraction, and these forces hold the particles together in the liquid state. The heat which we supply to water during boiling is used to overcome these forces of attraction between the particles so that they become totally free and change into a gas. This latent heat does not increase the kinetic energy of water particles, and hence, temperature does not rise during the boiling of water.

(ii) By boiling carbon dioxide is driven off and the soluble hydrogen carbonates are converted into insoluble carbonates and could be removed by filtration or decantation.
Ca(HCO₃)₂ → CaCO₃ + H_zO + CO₂
Calcium carbonate and magnesium carbonate are precipitated leaving the water soft. This is however, not very practical when large quantities of water are concerned.

(c) Give electron dot diagram of the following :
(i) Magnesium chloride
(ii) Nitrogen
(iii) Methane
(iv) Hydrogen chloride
Answer:

Question 6.
(a) Write the process of removal of hardness by Clark’s process.
(b) Give difference between a deliquescent substance and a hygroscopic substance.
(c) What are photochemical and electrochemical reactions ?
Answer:
(a) Clark’s process : A more practical method is to add a calculated quantity of slaked lime. The following reaction takes place.
Ca(HCO₃)₂ + Ca(OH)₂ → 2CaCO₃ + 2H₂O
Mg(HCO₃)₂ + Ca(OH)₂ → MgCO₃ + CaCO₃ + 2H₂O
Lime is first thoroughly mixed with water in a tank and then fed into another tank con­taining the hard water. Revolving paddles thoroughly mix the two solutions. Most of the calcium carbonate settles down. If there is any solid left over it is removed by a filter. The process goes by the name of Clark’s process.

(b)

Deliquescent substances	Hygroscopic substances
Water-soluble salts absorb moisture from the atmosphere and dissolve in it to form a saturated solution. The substance is called a deliquescent substance and the phenomenon is called deliquescence.	When a substance can absorb moisture from the air without changing its state (solid/liquid), the substance is called hy­groscopic and the phenomenon is known as hygroscopy.
They are solid crystalline in nature.	They may be crystalline solid or liquids.
They absorb moisture from the atmosphere and dissolve in it to form a saturated solution.	They absorb moisture from the atmo­sphere and dissolve in it but do not form a saturated solution.
Examples : Caustic soda (NaOH), caustic Potash (KOH), magnesium chloride (MgCy, zinc chloride (ZnCl2), ferric chloride (FeCl2).	Examples : Copper oxide (CuO), calcium oxide (CaO), copper sulphate (CuSO4), concentrated sulphuric acid (H2SO4).

(c) 1. Photochemical reaction : It is a reaction that occurs with the absorption of light energy.
Examples : Photosynthesis

2. Electrochemical reactions : It is a reaction that occurs with absorption of electrical energy.
Examples: (i) Fused potassium chloride, on passing current through it, breaks into charged particles of potassium and chloride.
\(\mathrm{KCl} \stackrel{\text { Electric current }}{\longrightarrow} \mathrm{K}^{+}+\mathrm{Cl}^{-}\)
(ii) Acidulated water breaks into hydrogen and oxygen.
\(2 \mathrm{H}_{2} \mathrm{O} \stackrel{\text { Electric current }}{\longrightarrow} 2 \mathrm{H}_{2}+\mathrm{O}_{2}\)

Question 7.
(a) Complete the following table :

Answer:
Atomic number of an element = No. of protons = No. of electrons Atomic number of phosphorus = 15 Therefore no. of protons in phosphorus = 15 And no. of electrons = 15

Mass number of an element = No. of protons + No. of neutrons Mass number of phosphorus = No. of protons + No. of neutrons 31-15 = 16 = No. of neutrons

Atomic number of an element = No. of protons = No. of electrons Atomic number of potassium = 19 Therefore No. of protons in potassium = 19 And No. of electrons = 19

Mass number of an element = No. of protons + No. of neutrons Mass number of potassium = 19 + 20 = 39

(b) Write the electronic configuration of the following :
(i) Potassium
(ii) Sulphur
Answer:
(i) Is² 2s² 2p⁶ 3s² 3p⁶ 4s¹
(ii) Is² 2s² 2p⁶ 3s² 3p⁴

(c) State the valency of the element having :
(i) 4 electrons in its valence shell
(ii) Having electronic configuration 2, 2
Answer:
(i) Valency is 4 and the element is silicon.
(ii) Valency is 2 and the element is beryllium.

ICSE Class 9 Chemistry Question Papers with Answers

ICSE Class 9 Chemistry Sample Question Paper 4 with Answers

Section-I
(Attempt all questions from this section)

Question 1.
(a) Fill in the blanks with the correct option given in brackets.
(i) Pollutants such as NO₂, SO₂ and SO₃ dissolved in the moisture of air are the cause of ………….. [water pollution/air pollution]
(ii) Excessive release of carbon dioxide in the atmosphere is the cause of ………….. effect which produces global warming. ………….. [green house/acid rain]
(iii) The ozone layer prevents the harmful radiation of the sun from reaching the earth. ………….. [UV/Infrared]
(iv) Decrease of the concentration of ozone in the stratosphere is the cause of formation of ………….. holes. [black/ozone]
(v) Base turns red litmus ………….. and acid turns blue litmus ………….. [blue/red]
Answer:
(i) Air Pollution
(ii) Green House
(iii) UV
(iv) Ozone
(V) Blue and Red

(b) Choose the correct answer from the options given below :
(i) The gas that prevents haemoglobin from carrying oxygen to different parts of the body is:
(A) Carbondioxide
(B) Carbon monoxide
(C) Hydrogen
(D) Nitrogen
Answer:
(A) Carbondioxide

(ii) Which element is more reactive than zinc ?
(A) Iron
(B) Calcium
(C) Hydrogen
(D) Mercury
Answer:
(B) Calcium

(iii) The isotopes of hydrogen are :
(A) Protium
(B) Deuterium
(C) Tritium
(D) All of the above
Answer:
(D) All of the above

(iv) The gas which has rotten egg smell is :
(A) Hydrogen sulphide
(B) Ammonia
(C) Sulphur dioxide
(D) Hydrogen chloride
Answer:
(A) Hydrogen sulphide

(v) What is the short from that stands for the atom of specific element ?
(A) Valency
(B) Molecular formula
(C) Radical
(D) Symbol
Answer:
(D) Symbol

(c) Name the following :
(i) An oxidising agent which does not contain oxygen.
(ii) A substance which oxidises concentrated HCl to chlorine.
(iii) A substance which will reduce aqueous iron (III) ions to iron (II) ions.
(iv) A liquid which is an oxidising agent as well as a reducing agent.
(v) A solid which is an oxidising agent.
Answer:
(i) Chlorine
(ii) MnO₂
(iii) H₂S
(iv) Hydrogen peroxide
(v) MnO₂

(d) Give reason for each of the following :
(i) Why bonds formed between metals and non-metals are ionic bonds ?
(ii) Dilute nitric acid cannot be used in the preparation of hydrogen.
(iii) Why non-metals form negative ions ?
(iv) Why hydrogen is not collected by the downward displacement of air ?
(v) Why group 17 elements are called most reactive non-metals ?
Answer:
(i) The metals have 1, 2 or 3 electrons in their valence shell. They have a tendency to lose their valence electrons. So, they combine with non-metals which have a tendency to gain electrons and thus form ionic bond.

(ii) Nitric Acid is a very strong oxidising agent. It oxidizes the dihydrogen gas produced during the reaction with metals to form water. That is why nitric acid cannot be used for preparation of hydrogen gas.

(iii) Non-metals form negative ions because non-metals have 5, 6 or 7 electrons in their valence shell and thus have a tendency to gain electron to form negative ions.

(iv) The hydrogen gas is highly combustible and gets oxidized when comes in contact of oxygen. This method is dangerous as the air and hydrogen mixture is explosive and therefore hydrogen is not collected by the downward displacement of air.

(v) Group 17 elements are called most reactive non-metals because they have 7 electrons in their outermost shell and need only 1 electron to become stable.

(e) What do you observe when :
(i) Ammonia reacts with hydrogen chloride gas.
(ii) Lead nitrate crystals are heated strongly.
(iii) The temperature of sodium nitrate and potassium nitrate is increased.
(iv) When barium chloride solution is mixed with sodium sulphate solution.
(v) Dilute hydrochloric acid is added to copper carbonate.
Answer:
(i) Change of state takes place and ammonia gas changes to solid ammonium chloride.
(ii) On heating lead nitrate decomposes to form lead (II) oxide, nitrogen dioxide and oxygen.
(iii) They show considerable increase in their solubilities with rise in temperature.
(iv) A white insolube precipitate of Barium sulphate is obtained.
(v) A brisk effervescence with the release of colourless, odourless, acidic gas that extinguishes glowing splint i.e., carbon dioxide gas is evolved.

(f) (i) State Charle’s law.
(ii) What is the significance of Boyle’s law ?
(iii) What is standard temperature and pressure ?
Answer:
(i) Charle’s law may be stated as volume of a given mass is directly proportional to its absolute temperature, if the pressure remains constant.
\(\frac{\mathrm{V}_{1}}{\mathrm{~T}_{1}}=\frac{\mathrm{V}_{2}}{\mathrm{~T}_{2}}=\mathrm{K}\) at constant Pressure.
Where V₁ is volume occupied by gas 1 at temperature T₁ and V₂ is volume occupied by gas 2 at temperature T₂.

(ii) On increasing pressure, volume decreases. The gas becomes denser. Thus at constant temperature, the density of a gas is directly proportional to its pressure. Atmospheric pressure is low at high altitudes, so air is less dense; hence, a lesser quantity of oxygen is available for breathing. This is the reason why mountaineers have to carry oxygen cylinders with them.

(iii) The standard temperature (T) of a gas is defined as the degree of hotness of that gas. The standard pressure (P) of a gas is the force that the gas exerts per unit area on the walls of its container.

(g) Balance the chemical equations given below :
1. Cl₂ + KBr → 2KCl + Br
2. KClO₃ → 2KCl + O₂
Answer:
1. Cl₂ + 2KBr → 2KCl + 2Br
2. 2KClO₃ → 2KCl + 3O₂

(ii) Identify the substance which matches the description given below :
1. It catches fire and bums with a lilac-coloured flame and produces hydrogen when reacted with water.
2. It acts as a dehydrating agent and removes water molecule from blue vitriol
3. A compound which produces carbon dioxide on heating.
Answer:
1. Potassium when reacts with water bums with a lilac-coloured flame.
2K + 2H₂O → 2KOH + H₂

2. Cone. H₂SO₄ removes water molecules from blue vitriol and acts as a dehydrating agent.

3. Calcium carbonate.

(h) Match Column A with Column B.

Column A	Column B
(i) Red colored compound changes to brown and then yellow	(A) Has 3 isotopes
(ii) Acid turns	(B) Blue litmus red
(iii) Hydrogen	(C) CCl3. NO2
(iv) Tear gas	(D) Copper Sulphate
(v) Caustic soda	(E) NaOH

Answer:
(i) (D) (ii) (B) (iii) (A) (iv) (C) (v) (E)

Section – II
(Attempt any four questions from this section)

Question 2.
(a) (i) What are alkaline earth metals ?
(ii) What are halogens ?
(b) What are catalysts and give its types ? Give one example of each ?
(c) Give three conditions for the formation of covalent bond ?
Answer:
(a) (i) The elements of group 13 such as Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba) and Radium (Ra) are alkaline earth metals, because k their oxides occur in the earth’s most and their hydroxides are weak alkalies. All the elements of this group have two valence electrons in their outermost orbit and show ‘ the valency 2.

(ii) Group 17 elements are known as halogens. The name halogens is derived from the Greek word halo which means sea and saltogens which means salt producing. These elements have 7 electrons in their outermost shell. They are all poisonous and have a similar strong pungent and unpleasant odour. They all have valency 1.

(b) Catalyst are those substances which increases or decreases the rate of a reaction without undergoing any change in themselves.

There are two types of catalyst:
1. Positive catalyst : When a catalyst accelerates a reaction, it is known as a positive 1 catalyst. Example : The rate of decomposition of hydrogen peroxide gets increased in the presence of manganese dioxide.
\(2 \mathrm{H}_{2} \mathrm{O}_{2} \stackrel{\mathrm{MnO}_{2}}{\longrightarrow} \mathrm{H}_{2} \mathrm{O}+\mathrm{O}_{2}\)

2. Negative catalyst: A catalyst employed to retard a reaction is known as a negative catalyst.
Example : Phosphoric acid retards the rate of decomposition of hydrogen peroxide.

(c) 1. Combining atom should be short by 1, 2 or 3 electrons in valence shell.
2. Electronegativity difference should be very small or zero between the two atoms.
3. Two atoms should approach one another accompanied by decrease of energy.

Question 3.
(a) (i) Why hydrogen gas is called a strong reducing agent ?
(ii) What is hydrogenation ?
(iii) Write two uses of hydrogen.
Answer:
(i) Hydrogen reduces the oxides of the less active metals i.e., it removes oxygen from strongly metal oxides when passed over them and itself gets oxidized to water.

(ii) In the presence of a catalyst like nickel, hydrogen directly combines with organic compounds that have double or triple bonds between two carbon atoms. This process is known as hydrogenation.

(iii) Uses of hydrogen :
1. Hydrogen is used as a fuel because of its high heat of combustion, hydrogen is used as a fuel in the form of coal gas, water gas and liquid hydrogen.
2. Hydrogen is used in Haber’s process for manufacture of ammonia, hydrogen chloride and methyl alcohol.

(b) (i) What is meant by group and period in a periodic table ?
(ii) What were the reasons to discard the law of octaves ?
(iii) Name two elements each one of which has two electrons in its outermost shell.
Answer:
(i) Vertical columns in the periodic table are called groups and the horizontal rows are called periods.
(ii) The law of octaves was discarded because of the following reasons :
1. The law of octaves was not applicable to the elements of higher atomic masses.
2. With the discovery of noble gases, it was found that it is the ninth element (not eight) that should have properties similar to first one.
(iii) 1. Magnesium (2,8,2)
2. Calcium (2, 8, 8, 2)

(c) Observe the following table showing the arrangement of elements and answer the questions given below the table :

1 2	13	14	15	16	17	18
Lithium		Carbon		Oxygen	L	Neon
X		5		G	Q
Y					R
Z					T

(i) Which is the most reactive metal ?
(ii) Which is the most reactive non-metal ?
(iii) Name the family of L, Q, R, T.
(iv) Name one element from group 15.
Answer:
(i) Z is the most reactive metal.
(ii) L is the most reactive non-metal.
(iii) Halogens.
(iv) Phosphorus is an element of group 15.

Question 4.
(a) At constant temperature, a gas occupies a volume of 2000 cm³ at a pressure of 740 mm of mercury. At what pressure will its volume be 500 cm³ ?
Answer:
Initial volume of the gas, V_x = 2000 cm³
Initial pressure of the gas, P_T = 740 mm Hg
Final volume of the gas, V₂ = 500 cm³
Final pressure of the gas P₂ = ?

(b) A given amount of gas A is confined in a chamber of constant volume. When the chamber is immersed in a bath of melting ice, the pressure of the gas is 100 cm Hg.
(i) What is the temperature when the pressure is 10 cm Hg ?
(ii) What will be the pressure when the chamber is brought to 100°C ?
Answer:
V₁ = V₂ = V
P_x = 100 cm Hg,
T₁ = 273 K,
P₂ = 10 cm Hg,
T₂ =?
\(\frac{P_{1} V_{1}}{T_{1}}=\frac{P_{2} V_{2}}{T_{2}}\)

(c) Gas A’ is a colourless gas which is produced by the reaction of active metals with dilute HCl. Gas ‘B’ is produced by the action of heat on potassium chlorate. Gas ‘A’ undergoes reaction with gas ‘B’ and forms a colourless liquid ‘C’.
(i) Identify A, B and C.
(ii) Give the balanced chemical equation for the formation of liquid ‘C’ from A’ and ‘B’.
(iii) Give two tests to identify liquid ’C’.
Answer:
(i) A – Hydrogen, B – Oxygen, C – Water

(ii) 2H₂ + O₂ 2H₂O

(iii) Liquid ‘C can be tested by the following two ways :
It turns white-coloured anhydrous copper sulphate blue.
It turns blue-coloured anhydrous cobalt chloride pink.

(iv) (a) SO₂ + H₂O → H₂SO₃ Sulphurous acid
(b Na₂O + H₂O → 2NaOH Sodium hydroxide
(c) NH₃ + H₂O → NH₄OH Ammonium hydroxide
(d) CO₂ + H₂O → H₂CO₃ Carbonic acid

(iv) Give the balanced chemical equation for the reaction of ‘C’ with :
(a) Sulphur dioxide
(b) Sodium oxide
(c) Ammonia
(d) Carbon dioxide

Question 5.
(a) (i) Name the isotopes of hydrogen which have mass number 2 and 3 respectively.
(ii) Why do the isotopes of an element have different physical properties ?
(iii) Which isotope of hydrogen has same number of each electron, proton and neutron ?
Answer:
(i) Two isotopes of hydrogen with mass number 2 and 3 are deuterium and tritium respectively.

(ii) The physical properties of the isotopes of an element are different due to the difference in the number of neutrons in their nuclei. The densities, melting points and boiling points etc., are slightly different.

(iii) Deuterium has equal number of electron, proton and neutron in it because it has atomic number one, which is equal to number of electrons and number of protons also.

(b) State the type of covalent bonding in the following molecules :
(i) Chlorine
(ii) Nitrogen
(iii) Oxygen
(iv) Hydrogen
Answer:
(i) Single covalent bond is present in chlorine.
(ii) Triple covalent bond is present in nitrogen.
(iii) Double covalent bond is present in oxygen.
(iv) Single covalent bond is present in hydrogen.

(c) Write the function of ozone layer.
Answer:
Function of Ozone layer :
1. The ozone layer acts as a blanket in the atmosphere above 16 km and prevents the harmful UV rays coming from the sun.
2. It protects life on earth from harmful effects of UV rays which cause skin cancer, destroys many organisms necessay for life in general.
3. The ozone absorbs UV rays of longer wavelength forming oxygen molecule and oxygen atom.

Question 6.
(a) (i) How do fish and aquatic animals survive when a pond is covered with thick ice ?
(ii) Name two elements whose properties were correctly predicted by Mendeleev. Mention their present-day name.
(b) Classify solution on the basis of solubility.
(c) Explain endothermic and exothermic reactions with the help of an example.
Answer:
(a) (i) Water has an unusual physical property. When cooled, it first contracts in volume, as do other liquids, but at 4°C (maximum density), it starts expanding and continues to do so till the temperature reaches 0°C , the point at which it freezes into ice. The property of anomalous expansion of water enables marine life to exist in the colder regions of the world, because even when the water freezes on the surface, it is still liquid below the ice layer.

(ii) Two elements whose properties were correctly predicted by Mendeleev are :
1. Eka-aluminium-Gallium
2. Eka-silicon-Germanium

(b) Solutions can be classified on the basis of their solubility, i.e. depending on the amount of solute which dissolves in a given solvent.

1. Unsaturated solution : If more solute can be dissolved in a solvent at a particular temperature, then the solution is called an unsaturated solution.
2. Saturated solution : If no more solute can be dissolved in a solvent at a particular temperature, then the solution is called a saturated solution.
3. Supersaturated solution : If the solution contains more of the solute, then the saturated solution at a particular temperature is called a ‘supersaturated solution.

(c) Reactions in which heat is given out along with the products are called exothermic reac­tions.
Example : Burning of methane gas releases a large amount of energy. Hence, it is an exothermic reaction.
CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)
Reactions which absorb energy or require energy in order to proceed are called endothermic reactions.
Example : When ammonium chloride is dissolved in water in a test tube, the test tube becomes cold. Thus, the reaction is an example of an endothermic reaction.

Question 7.
(a) Describe Bohr’s atomic model of an atom.
(b) The table given below shows the mass number and atomic number of five elements A, B, C, D and E.

Element	Mass number	Atomic number
A	35	17
B	23	11
C	12	6
D	16	8
E	40	18

(i) To which group and period does element A belong ?
(ii) Choose from A, B, C, D and E, metal, non-metal and inert gas.
(c) State Newland’s law of octaves.
Answer:
(a) In 1913, Niels Bohr, a Danish physicist, explained the causes of the stability of the atom in a different manner.

Niels Bohr revised Rutherford’s atomic model and put forth the following suggestions :
1. Electrons possess a specific amount of energy which allows them to revolve around the nucleus.
2. An atom contains discrete orbits which correspond to a specific amount of energy.
3. Hence, these orbits are also known as energy levels.
4. The energy levels of an atom are represented as K, L, M, N and so on or the numbers n = 1, 2, 3, 4 and so on.

5. The electrons are confined to these energy levels. While revolving in these discrete orbits, electrons do not radiate energy. Hence, these orbits are also known as ‘stationary orbits’ or ’stationary shells’. Smaller the size of the orbit, smaller is its energy.
6. As we move away from the nucleus, the energy of the orbit increases progressively.
7. The transfer of an electron from one orbit to another is always accompanied with absorp¬tion or emission of energy.
8. When an electron jumps from a lower energy level to a higher energy level, it absorbs energy.
9. When an electron returns from a higher energy level to a lower energy level, it emits energy.

(b) (i) Group = 17
Period 3 (ii) Metal = B
Non-metal = A, D, C Inert gas = E

(c) “If elements be arranged in ascending order of their atomic masses, the properties of eighth element was repetition of properties of first element.” The repetition resembles repetition of eighth note in an octave of music so it is known as law of octaves.

ICSE Class 9 Chemistry Question Papers with Answers

ICSE Class 9 Chemistry Sample Question Paper 3 with Answers

Section -1
(Attempt all questions from this Section)

Question 1.
(a) Fill in the blanks with the correct choice given in brackets.
(i) The number of shells is equal to the number of …………….. [valence electrons/protons]
(ii) Mendeleev’s periodic table contains vertical columns called …………… [groups/periods]
(iii) The chemical reaction that takes place in the presence of light are known as …………….. [photolysis/endothermic]
(iv) The molecular formula of baking soda is ………….. [NaHCO₃/CaCO₃]
(v) …………… pollution is the effect of undersirable changes in our surroundings that have harmful effects on plants, animals and human beings. [Sound/Environmental]
Answer:
(i) Valence electrons
(ii) Groups
(iii) Photolysis
(iv) NaHCO₃
(v) Environmental.

(b) Choose the correct answer from the options given below :
(i) The following causes nausea and irritation in the eyes and the throat.
(A) Hydrogen sulphide
(B) Oxygen
(C) Carbon monoxide
(D) Nitrogen oxide
Answer:
(A) Hydrogen suiphide

(ii) How many horizontal rows are there in the modem periodic table ?
(A) 7
(B) 5
(C) 8
(D) 10
Answer:
(A) 7

(iii) A solution may be formed by mixing :
(A) A liquid with a gas
(B) A solid with a liquid
(C) A liquid with another liquid
(D) All of the above
Answer:
(D) All of the above

(iv) The S. I. unit of pressure is :
(A) Joule
(B) Doctor
(C) Pascal
(D) Celsius
Answer:
(C) Pascal

(v) The temperature of 0° Kelvin on the Celsius scale is equal to :
(A) – 273 C
(B) + 273 C
(C) 0 C
(D) 100 C
Answer:
(A) – 273C

(c) Name the following :
(i) An oxidising agent which does not contain oxygen.
(ii) A substance which oxidises concentrated HCl to chlorine.
(iii) A substance which will reduce aqueous iron (III) ions to iron (II) ions.
(iv) A liquid which is an oxidising agent as well as a reducing agent.
(v) A solid which is an oxidising agent.
Answer:
(i) Cl (Chlorine)
(ii) MnO₂ (Manganese oxide)
(iii) H₂S (Hydrogen sulphide)
(iv) H₂O₂ (Hydrogen peroxide)
(v) MnO₂ (Manganese oxide)

(d) Give a reason for each of the following :
(i) Why the three elements chlorine (35.5), bromine (80) and iodine (127) form a triad?
(ii) Why hydrogen belongs to the first group and the first period of the periodic table?
(iii) Why hydrogen-oxygen mixture is called detonating mixture?
(iv) Why washing soda, when exposed to air becomes a monohydrate?
(v) Why noble gases are called chemically inactive gases?
Answer:
(i) 1. All are non-metals.
2. All of them reacts with water to form acids.
3. All have valency 1.

(ii) Hydrogen in the first element in the periodic table. Its atomic number is 1, and it has only 1 electron in its valence shell. Therefore, it belongs to the first group in the first period of the periodic table.

(iii) Hydrogen is a highly reactive fuel. When hydrogen molecules react with oxygen, new molecular bonds are formed which results in an explosive release of energy and the production of water.

(iv) Washing soda, when exposed to air becomes a monohydrate because it loses its water of crystallisation on exposure to air.
\(\mathrm{Na}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O} \stackrel{\text { Dry air }}{\longrightarrow} \mathrm{Na}_{2} \mathrm{CO}_{3} \cdot \mathrm{H}_{2} \mathrm{O}+9 \mathrm{H}_{2} \mathrm{O}\)
(v) Noble gases are called chemically inactive gases because they have 8 electrons in their outermost shell, so they cannot gain or lose electrons. Therefore, they are chemi¬cally inactive.

(e) What do you observe when :
(i) When dilute sulphuric acid is added to given unknown substance.
(ii) When ammonium dichromate is heated.
(iii) When white crystalline solid is heated.
(iv) When mercuric oxide is heated.
(v) When iron pieces are dropped into a blue coloured copper sulphate solution.
Answer:
(i) A colourless gas with a foul smell, as of rotten eggs is evolved. Gas evolved is hydrogen sulphide.
(ii) The orange colour of -the substance changes to green colour and water vapour and nitrogen gas are produced.
(iii) It sublimates to form a basic NH₂ gas and an acidic gas (HCl).
(iv) It decomposes to form two elements one is mercury and the other is oxygen.
(v) The blue colour of the solution fades and turns into light green due to formation of ferrous sulphate.

(f) (i) What is gas ?
(ii) What is absolute zero temperature ?
(iii) What is standard temperature and pressure ?
Answer:
(i) The state of matter in which inter-particle attraction is weak and inter-particle space is so large that the particles become completely free to move randomly in the entire available space is known as gas.

(ii) The temperature at which the molecular motion completely ceases (theoretical concept), on the Kelvin scale is absolute zero.

(iii) The standard temperature (T) of a gas is defined as the degree of hotness of that gas. Whereas the standard pressure (P) of a gas is the force that the gas exerts per unit area on the walls of its container.

(g)(i) Balance each of the chemical equations given below :
1. Cu + H₂SO₄ → CuSO₄ + SO₂ + H₂O
2. KCl → K + Cl₂

(ii) Identify the substance which matches the description given below :
1. Which turns lime water milky ?
2. Which results in the formation of sodium carbonate on heating ?
3. Which when heated sublimates to form violet vapours ?

(h) Match Column A with Column B.

	Column A	Column B
(i)	Blue salt changes to white and then black.	(A) Ammonium dichromate
(ii)	Orange coloured compound changes to green.	(B) Iodine
(iii)	Red coloured compound changes to Brown and then yellow.	(C) Zinc nitrate
(iv)	White to yellow when hot and white when cold.	(D) Copper sulphate
(v)	Violet solid changes to violet vapours.	(E) Red lead

Section – II
(Attempt any four questions from this section)

Question 2.
(a) The formula of the chloride of a metal ‘M¹ is MO₂. State the formula of its :
(i) Nitrogen
(ii) Hydrogen
(iii) Carbon
Answer:
(i) Nitrogen dioxide
(ii) Hydrogen peroxide
(iii) Carbon dioxide

(b) Write balanced chemical equations for each of the following :
(i) Preparation of ammonia by ammonium chloride and calcium hydroxide.
(ii) When potassium dichromate reacts with hydrochloric acid.
(iii) Reaction of iron with water.
Answer:
(i) 2NH₄Cl + Ca(OH)₂ → CaCl₂ + 2NH₃ + 2H₂O 2KCl
(ii) K₂Cr₂O₇ + 14HCl → 2KCl+ 2CrCl₃ + 7H₂Q + 3Cl₂
(iii) 2Fe + 3H₂O → Fe₂O₃ + 3H₂

(c) Draw the orbit structure for each of the following compounds :
(i) Sodium chloride [Na = 11 and Cl = 17]
(ii) Magnesium
(iii) Oxygen
(iv) Argon
Answer:

Question 3.
(a) (i) Name the industrial method for the production of hydrogen gas.
(ii) Name the promoter used in the above process.
(iii) Write one test for hydrogen.
Answer:
(i) Bosch process is the name of the industrial method for the production of hydrogen gas.
(ii) Chromic oxide (Cr₂O₃) acts as a promoter in Bosch process.
(iii) Hydrogen bums silently in air or oxygen with a pale blue flame, forming water.
2H₂ + O₂ → 2H₂O

(b) (i) What is periodic table ?
(ii) Why periodic table is called periodic table ?
(iii) What is the reason for discarding the law of triad ?
Answer:
(i) Periodic table is a chart of elements prepared in such a way that elements with similar
properties occur in same vertical column or group.
(ii) It is called periodic because elements with similar properties occur at fixed intervals or periods and it is called a table because elements are arranged in tabular forms.
(iii) 1. Dobereiner failed to arrange all the then known elements in a triad.
2. The law did not fully apply even within the same family.
(c) The d-block elements are known as transition elements. They are included in groups 3 to 12.

(c) What are transition elements ? Give examples and also write their main characteristics :
Answer:
The d-block elements are known as transition elements. They are included in groups 3 to 12.
Their main characteristics are as follows :
1. All these elements are metals with high melting and boiling points.
2. They are good conductors of heat and electricity.
3. Most of these elements are used as catalysts.
4. Some of these elements are attracted towards a magnet.
5. Most of these elements exhibit variable valencies.
6. Most of these elements form coloured ions and coloured compounds.
Some of the d-block elements are : Scandium, Titanium, Iron and Cobalt etc.

Question 4.
(a) At what temperature will 500 cm³ of a gas measured at 20°C occupy half its volume ? The pressure is kept constant.
Answer:

(b) The volume of a given mass of a gas with some pieces of marble in a container at 760 mm Hg pressure is 100 ml. If the pressure is changed to 1000 mm Hg, the new volume is 80 ml. Find the volume occupied by the marble pieces, if the temperature remains constant.
Answer:
Let the volume occupied by the marble pieces = V ml.
At 760 mm Hg, the volume occupied by the gas = (100 – V)
At 1000 mm Hg, the volume occupied by the gas = (80 – V)
By Boyle’s law,  P₁V₁ = P₂V₂760 x (100 – V) – 1000 x (80 – V)
Or 24 V = 400 ml
Or  V = 16.6 ml
The required volume = 16.6 ml.

(c) Calculate the relative molecular mass of each of the following :
(i) Ammonium dichromate [(NH₄)₂Cr₂O₇]
(ii) Methane (CH₄)
Answer:
(i) Molecular masses of the elements :Nitrogen : 14.007 g/mol
Hydrogen : 1.00794 g/mol
Chromium : 51.9961 g/mol
Oxygen : 15.999 g/mol
Molecular mass of ammonium dichromate
= (2 x 14.007) + (8 x 1.00794) + (2 x 51.9961) + (7 x 15.999) = 252.06 g/mol

(ii) Atomic mass of carbon = 12.011
Atomic mass of hydrogen = 1.00794
Molecular mass = 12.011 + (1.00794 x 4)
Molecular mass of methane = 16.04276 g/mol

Question 5.
(a) (i) Describe the “plum pudding” model of the atom ?
(ii) Compare Dalton’s atomic theory with the modem atomic theory.
Answer:
(a) (i) After the discovery of electrons and protons J. J Thomson proposed “plum pudding” model of the atom. According to this model :
1. An atom is considered to be a sphere of uniform positive charge and electrons are embedded into it.
2. The total positive charge is equal to the total negative charge so that an atom as a whole is electrically neutral.
3. The mass of an atom is considered to be uniformly distributed

Dalton’s atomic theory	Modem atomic theory
Atoms are indivisible particles.	Atoms are divisible into sub-atomic particles like protons, electrons and neutrons.
Atoms can neither be created nor be destroyed.	Atoms can be created and destroyed by nuclear fission and fusion.
Atoms follow the law of chemical combination to form compounds.	In the formation of organic compounds, the laws of chemical combination are not always followed.

(b) State the type of covalent bonding in the following molecules :
(i) Ethyne
(ii) Ammonia
(iii) Oxygen
Answer:
(i) Triple covalent bond is present in ethyne.
(ii) Single covalent bond is present in ammonia.
(iii) Double covalent bond is present in oxygen.

(c) How would you distinguish between the following pairs of substances on the basis of the tests given in brackets ?
(i) Sodium chloride and potassium chloride (flame test)
(ii) Zinc and sodium sulphite (action of dilute sulphuric acid)
Answer:
(i) When flame test is performed on the above given substances the following
observations are made :

(ii) When dilute sulphuric acid is passed through the zinc and then it is warmed, vigorous effervescence occurs and a colourless, odourless gas evolves.
Zn + H₂SO₄ → ZnSO₄ + H₂
When dilute sulphuric acid is passed to the (Sodium sulphite) and then it is warmed, a colourless gas with suffocating smell of burning sulphur is evolved.
Na₂SO₃ + H₂SO₄ → Na₂SO₄ + H₂O + SO₂

Question 6.
(a) Explain why water is called as “Universal solvent” ?
(b) Write the importance of air dissolved in water.
(c) Write two types of chemical reactions with examples of each.
Answer:
(a) Water is remarkable solvent. It dissolves many substances, forming aqueous solutions. Water has a high dielectric constant. As a result, it reduces the electrostatic force of attraction between positive and negative ions and dissolves even inorganic compounds, which are usually electrovalent. Not only solids, but also gases and other liquids dissolve in water. Hence, it is difficult to find absolutely pure water in nature. For the same reason, water is called a universal solvent.

(b) Air dissolved in water is biologically important.
1. Marine life, like fish, use the oxygen of the air dissolved in water for respiration and thus aquatic life is sustained.
2. Aquatic plants make use of dissolved carbon dioxide for photosynthesis e., to prepare their food.
3. Carbon dioxide dissolved in water reacts with limestone to form calcium bicarbonate. Marine organisms such as snails, oysters, etc., extract calcium carbonate from calcium bicarbonate to build their shells.

(c) Types of chemical reactions :
1. Direct combination reactions : A reaction in which two or more substances combine to form a single substance is called a combination reaction.
A + B → AB
Example : Photosynthesis reaction
The reaction of photosynthesis is also a combination reaction, which is endothermic. It takes place in the presence of sunlight where small molecules of carbon dioxide and water are used to make glucose.
\(6 \mathrm{CO}_{2}+6 \mathrm{H}_{2} \mathrm{O} \stackrel{\text { Sunlight and chlorophyll }}{\longrightarrow} \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+6 \mathrm{O}_{2}\)
The green pigment chlorophyll is essential for this reaction, because it traps energy from the sun.

2. Decomposition reaction : It is the breaking up of a compound either into elements or simpler compounds, such that these products do not recombine to form the original compound. A decomposition reaction that is brought about by heat is known as thermal decomposition.
Example : The compound mercuric oxide, when heated decomposes to form two elements, mercury and oxygen.
2HgO(s) → 2Hg(l) + O₂

Question 7.
(a) Complete the following table :

(b) If K and L shells of an atom are full, then what would be the number of electrons in the atom?
(c) From the symbol \(\frac{31}{15} \mathrm{P}\) state.
(i) Electronic configuration of phosphorus
(ii) Mass number of phosphorus.
Answer:
(a) (i) Atomic number = Number of electrons = Number of Protons = 1 Mass number = Number of protons + Number of neutrons
= 11 + 12 = 23

(ii) Atomic number = Number of electrons = Number of Protons
= 16

S. No.	Element	Mass Number	Atomic Number	Number of Electrons	Number of Protons	Number of Neutrons
(i)	Sodium	23	11	12	11	12
(ii)	Sulphur	32	16	16	16	16

(b) Maximum number of electrons in K shell = 2 Maximum number of electrons in L shell = 8
If an atom has completely filled shells, then it has 2 and 8 electrons in K and L shell respectively.
Hence, total number of electrons in the atom = 2 + 8 = 010.

(c) (i) 2,8,5 (ii) 31

ICSE Class 9 Chemistry Question Papers with Answers

ICSE Class 9 Chemistry Sample Question Paper 2 with Answers

Section -1
(Attempt all questions from this section)

Question 1.
(a) Fill in the blanks with the correct choice given in brackets.
(i) The atomic number of an element is the number of ………………. and electrons present in the nucleus of an atom. [protons/negative charge]
(ii) As one moves down a group, size of atoms of successive elements ……………………….. [increases/ decrease
(iii) When zinc reacts with dilute sulphuric acid………………………… gas is evolved. [carbon dioxide/hydrogen]
(iv) Anode rays are made up of …………………. charged particles, [positively/negatively]
(v) Elements which have 4 or 5 or 6 or 7 electrons in their outermost shell are ……………………..
Answer:
(i) Proton
(ii) Increases
(iii) Hydrogen
(iv) Positively
(v) Non-metal

(b) Choose the correct answer from the options given below :
(i) The ozone layer protects us from the sun’s harmful. rays.
(A) UV rays
(B) X rays
(C) Gamma rays
(D) Beta rays
Answer:
(A) UV Rays

(ii) The three elements calcuium, strontium and barium have the following similarities :
(A) All are metals
(B) Each has an oxide that is alkaline in nature
(C) Each has valency 2
(D) All of the above
Answer:
(D) All of the above

(iii) The specific value of latent heat of vaporization of water is :
(A) 2286 J/g
(B) 540 cal/g
(C) 336 J/g
(D) Both A and B
Answer:
(D) Both A and B

(iv) The gas that turns lime water milky is :
(A) Carbon dioxide
(B) Oxygen
(C) Hydrogen
(D) Nitrogen
Answer:
(A) Carbon dioxide

(v) Gases exert pressure in :
(A) One direction
(B) All directions
(C) Two directions
(D) None of the above
Answer:
(B) All directions

(c) Name the gas evolved in each of the following cases :
(i) When an electric current is passed through accumulated water.
(ii) Copper carbonate is heated strongly.
(iii) Nitrogen combines with hydrogen.
(iv) When mercuric oxide is heated.
(v) Addition of sodium to cold water.
Answer:
(i) Hydrogen and oxygen
(ii) Carbon dioxide
(iii) Ammonia
(iv) Mercury and oxygen
(v) Hydrogen.

(d) Give a reason for each of the following :
(i) Why Water is an excellent liquid to use in cooling systems ?
(ii) A solution is always clear and transparent.
(iii) Lakes and rivers do not suddenly freeze in the winters.
(iv) A solute cannot be separated from a solution by filtration.
(v) Fused CaCl₂ or cone. H₂SO₄ is used in desiccators.
Answer:
(i) Water is an excellent liquid to use in cooling systems because of its ability to absorb large quantities of heat as a cooling agent.

(ii) A water-soluble solid disappears in a solution where the solvent is water, and water has the property of being clear and transparent. So, the solution is also always clear and transparent.

(iii) Lakes and rivers do not freeze suddenly in winters because of the high specific latent heat of solidification, i.e., the amount of heat released when 1 g of water solidifies to from 1 g of ice at 0°C. It is about 336 J/g or 80 cal/g.

(iv) The component which dissolves in a solvent is known as a solute. So, it can be separated from a solution by the filtration process. However, the filtration process is applicable only when the solute is insoluble in the solution. So, the solute cannot be separated from the solution by filtration.

(v) Anhydrous calcium chloride or cone. H₂SO₄ is a drying agent that can readily absorb moisture from other substances without chemically reacting with them. So, it is used in desiccators.

(e) What do you observe when :
(i) Mercuric chloride and potassium iodide is rubbed.
(ii) Ammonia reacts with oxygen.
(iii) A solution of silver nitrate is kept in sunlight.
(iv) Lead sulphide is heated.
(v) Barium chloride is added to dilute sulphuric acid.
Answer:
(i) They give a scarlet coloured substance called mercuric iodide.
(ii) It produces nitric oxide and water vapour in the presence of a catalyst.
(iii) It decomposes in the presence of sunlight and releases oxygen gas.
(iv) It reacts with oxygen to form white lead sulphate.
(v) A thick white precipitate is formed.

(f) (i) State Boyle’s law.
(ii) What is the significance of Boyle’s law ?
(iii) Convert the temperature of 45°C to the Kelvin scale.
Answer:
(i) Boyle’s law states that volume of a given mass of a dry gas is inversely proportional to its pressure at constant temperature.
Mathematical expression of this law is :
Suppose a gas occupies volume V₁ when its pressure is P₁: then
\(\mathrm{V}_{1}=\frac{1}{\mathrm{P}_{1}} \text { or } \mathrm{V}_{1}=\frac{\mathrm{K}}{\mathrm{P}_{1}}\)
P₁V₁ = K = constant

If V₂ is the volume occupied when its pressure is P₂ : then
\(\mathrm{V}_{2}=\frac{1}{\mathrm{P}_{2}} \text { or } \mathrm{V}_{2}=\frac{\mathrm{K}}{\mathrm{P}_{2}}\)
Or     P₂V₂ = K = constant
P₁V₁ = P₂V₂ = K at constant temperature

(ii) On increasing pressure, volume decreases. The gas becomes denser. Thus at constant temperature, the density of a gas is directly proportional to its pressure. Atmospheric pressure is low at high altitudes, so air is less dense; hence, a lesser quantity of oxygen is available for breathing. This is the reason why mountaineers have to carry oxygen cylinders with them.

(iii) Temperature on Celsius scale = 45°C
from the formula
T (in °C) + 273.15 = T (in K)
45 + 273.15 = T (in K)
T = 318.15 K

(g) (i) Balance the chemical equations given below :
1. Cl₂ + KBr → 2KCl + Br
2. 2KClO → 2KCl + O₂

(ii) Identify the substance which matches the description given below :
1. A nitrate which produces oxygen as the only gas.
2. A compound which produces carbon dioxide on heating.
3. An element which does not contain neutron.

(h) Match Column A with Column B.

Column A	Column B
(i) Hydrogen	(A) Magnesium chloride
(ii) Ionic bond	(B) Nitrogen family
(iii) Group 15	(C) Anions
(iv) Negative ions	(D) Boyle’s law
(v) P1V1 = P2V2	(E) Has 3 isotopes

Answer:
(i) (E) (ii) (A) (iii) (B) (iv) (C) (v) (D)

Section – II
(Attempt any four questions from this section)

Question 2.
(a) A metal exists as a liquid at room temperature is obtained by heating its sulphide ore in the presence of air.
(i) Name the metal and write its chemical symbol.
(ii) Write the name and formula of its sulphide ore.
(iii) Name a common device in which the metal is used.
Answer:
(i) Mercury (Hg)
(ii) Name of sulphide ore : Cinnabar, formula : HgS
(iii) Thermometer

(b) Write balanced chemical equations for each of the following
(i) Reaction of lime with water.
(ii) Reaction of copper sulphate solution with iron metal.
(iii) Addition of zinc to aqueous solution of copper sulphate.
Answer:
(i) When lime is reacted with water, it reacts vigorously and forms calcium hydroxide.
CaO + H₂O → Ca (OH)₂

(ii) When a piece of iron metal is placed in the copper sulphate solution then iron sulphate solution and copper metal are formed.
CuSO₄ + Fe → FeSO₄ + Cu

(iii) When zinc metal is placed in copper sulphate solution, then zinc sulphate solution and copper are obtained.
CuSO₄ + Zn → ZnSO₄ + Cu

(c) Draw the orbit structure for each of the following :
(i) Isotopes of carbon with mass number 12
(ii) Magnesium
Answer:
(i) Isotopes of Carbon with mass number 12

Question 3.
(a) (i) Write a short note on hydrogen.
(ii) Write physical properties of hydrogen.
(iii) Write those properties of hydrogen which differ from those of alkali metals and halogens ?
Answer:
(i) Hydrogen is the first element in the periodic table. Its atomic number is 1, and it has only one electron in ifs valence shell. Therefore, it belongs to the first group and first period in the periodic table.

(ii) Physical properties of hydrogen are :
(a) It is colorless, odourless and tasteless.
(b) Non-toxic in nature.
(c) Liquefies at below -240°C under pressure of about 20 atmosphere.

(iii) 1. Hydrogen atom has only one shell but alkali metals and halogens have two or more shells.
2. Oxides of hydrogen, H₂O is a neutral oxide. Oxides of halogens like Cl₂O, Cl₂O₇ are acidic in nature, while oxides of alkali metals like Na₂O, K₂O are basic in nature.

(b) (i) What is meant by periodicity of properties ?
(ii) Why are the elements of group 17 called halogens ?
(iiii) Elements of which group are called the noble gases ?
Answer:
(i) Repetition of properties after a certain interval is called periodicity of properties.
(ii) The elements of group 17 are called halogens because the elements of this group form salts with group 1 elements and the name halogen is derived from the Greek halogen which means salt former.
(iii) Elements of group 18 are called noble gases.

(c) (i) How do we classify the elements ?
(ii) In Mendeleev’s periodic table, why was there no mention of noble gases like helium, neon and argon ?
(iii) Arrange the following elements in the increasing order of atomic sizes :
Li, Na, Cs, Rb, Fr, K
Answer:
(i) We classify the elements according to their properties so that we can have an orderly arrangement of elements and may study such a large number of elements comfortably.
(ii) Mendeleev believed that certain more elements existed but were not discovered till that time. Hence, he left some gaps in his periodic table so that these gaps would be filled later after the discovery of elements.
(iii) Li < Na < K < Rb < Cs < Fr

Question 4.
(a) A given mass of a gas occupies 572 cm³ at 13°C and 725 mm Hg pressure. What will be its volume at 24°C and 792 mm Hg pressure ?
(b) Write the Gas Equation e., pressure, volume and temperature relationship.
(c) Calculate the relative molecular mass of each of the following :
(i) H₂O
(ii) Methanol
Answer:
(a) P₁ = 725 mm of Hg, V, = 572 cm³, = (273 + 13) K = 286 K, P₂ = 792 mm Hg, V₂ = ? cm³
T₂ = (273 + 24) K = 297 K.
Applying the gas equation,

The required volume of the gas is 543.75 cm³.

(b) If both pressure and temperature of a fixed mass of a gas are varied, a combination of Boyle’s law and Charle’s law gives us a fixed relation amongst its volume, pressure and temperature.
According to Boyle’s law
\(\mathrm{V}=\frac{\mathrm{K}}{\mathrm{P}}\)

Now, on combining the two laws, volume of a given mass of a gas varies inversely with pressure and directly with absolute temperature.
\(\frac{\mathrm{PV}}{\mathrm{T}}=\text { Constant }\)

Accordingly, if the volume of a given mass of a gas changes from V₁ to V₂, its pressure from P₁ to P₂ and its temperature from T₁ to T₂ then
\(\frac{P_{1} V_{1}}{T_{1}}=\frac{P_{2} V_{2}}{T_{2}} \)
The above mathematical expression is called gas equation.

(c) (i) The molecular mass of water, H₂O
= (2 x Atomic mass of hydrogen) + (1 x Atomic mass of oxygen)
= [2(1.0084 u) + 1 (16.00 u)] = 2.016 u + 16.00 u = 18.016 = 18.02 amu

(ii) The molecular mass of Methanol i.e., CH₃OH is
= (atomic mass of C) + (3 x atomic mass of H) + (atomic mass of O) + (atomic mass of H)
= (12 + 3 x 1 + 16 + 1) = 32 a.m.u.

Question 5.
(a) Elements of the periodic table with atomic numbers from 3 to 18 are shown in the table below. Some elements are shown by letters even though the letters are not the usual symbols of the elements.

3	4	5	6	7	8	9	10
A	B	C	D	E	F	G	H
11	12	13	14	15	16	17	18
I	J	K	L	M	N	O	P

Which of these is ?
(i) A noble gas
(ii) A halogen
(iii) An alkali metal
(iv) An element with valency 4
Answer:
(i) H and P are noble gases.
(ii) G and O are halogens.
(iii) A and I are alkali metals.
(iv) D and L have valency 4.

(b) Write the electronic configuration of the following :
(i) Indium (In)
(ii) Titanium (Ti)
Answer:
(i) Is² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p¹
(ii) Is² 2s² 2p⁶ 3s² 3p⁶ 3d² 4s²

(c) Write down in detail the defects of Mendeleev’s periodic table.
Answer:
The defects in Mendeleev’s periodic table are as follows :
1. Anomalous pairs : Argon with atomic mass 39.9 precedes potassium with atomic mass 39.1. Cobalt with atomic mass 58.9 precedes nickel with atomic mass 58.6. Tellurium with atomic mass 127.6 precedes iodine with atomic mass 126.9.

2. Position of isotopes : According to Mendeleev’s periodic law, isotopes of an element must be given separate places in the periodic table. Although they have different atomic masses but they were not assigned separate places.

3. Grouping of chemically dissimilar elements : Elements such as copper and silver bear no resemblance to alkali metals (lithium, sodium etc.) but they have been placed together in the first row.

4. Separation of chemically similar elements : Elements those are chemically similar, such as gold and platinum have been placed in separate groups.

5. Electron arrangement : It does not explain the electron arrangement of elements.

Question 6.
(a) Write three factors affecting solubility.
(b) What is Soft water and Hard water and also describes the types of hardness?
(c) Classify each of the following reactions as synthesis, decomposition, displacement or double decomposition :
(i) 2CO(g) + O₂ → 2CO₂(g)
(ii) \(2 \mathrm{HgO}(\mathrm{s}) \stackrel{\text { (heat) }}{\longrightarrow} 2 \mathrm{Hg}(\mathrm{l})+\mathrm{O}_{2}(\mathrm{~g})\)
(iii) CuSO₄ + Zn → ZnSO₄ + Cu↓
(iv) BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl
Answer:
(a) The rate of dissolution of a solid in a liquid depends on the following factors :
1. Size of solute particles : The smaller the size of the solute particle, the greater is its total surface area exposed to the solvent. Therefore, the greater is the solubility of that solute.
2. Stirring : This brings more of the solvent in contact with the solute and thus
increases the rate of formation of solution.
3. Temperature : The solubility of a gas in a liquid always decreases with rise in temperature.

(b) Water is said to be soft if it readily forms lather with soap. Pure water or water containing sodium salts easily gives lather with soap. Such water is called soft water.
Hard water contains bicarbonates, chlorides or sulphates of calcium or magnesium that is why it does not readily form lather with soap.
There are two types of Hardness :
1. Permanent Hardness : This type of hardness cannot be removed by boiling.
2. Temporary Hardness : It is due to the presence of bicarbonates of calcium and magnesium. It can be easily removed by boiling.

(c) (i) Synthesis reaction : Where two substances combine to form a single substance. In
the above reaction, carbon monoxide, a compound bums in the presence of oxygen to form a single product named carbon dioxide.

(ii) Decomposition reaction : Where breaking up of compound into simpler compounds takes place. In the above reaction, the compound mercuric oxide when heated decomposes to form 2 element mercury and oxygen.

(iii) Displacement reaction : Where a more reactive element displaces a less reactive element. In the above reaction, when pieces of zinc are added to copper sulphate solution, the blue colour of the solution fades and becomes colourless and at the same time reddish brown particles of copper settle down in the beaker.

(iv) Double displacement reaction : Where two compounds react to form two new compounds by mutual exchange of radicals. This is an example of precipitation reaction in which two compounds in their aqueous state react to form an insoluble salt.

Question 7.
(i) Who discovered atom and write the main postulates of Dalton’s atomic theory ?
(ii) What do you mean by orbits and nucleus ?
(iii) What are valence electrons ?
Answer:
(i) The Greek philosopher Democritus called the parmanu an “atom”, which means “indivisibles”. But the first scientific theory about the structure of matter was given by “John Dalton”.
Main postulates of Dalton’s atomic theory are :
1. Matter consists of very small and indivisible particles called atoms.
2. Atoms can neither be created nor destroyed.
3. Atoms of an element combine in small number to form molecules.
4. Atoms are the smallest unit of matter that can take part in chemical reaction.
5. The atoms of an element are alike in all respects but they differ from the atoms of other elements.
6. Atoms of one element combine with atoms of another element to form molecules of a compound.

(ii) Orbits : It is the imaginary path where electrons revolve around the nucleus of an atom.
Nucleus : The protons and neutrons collectively called nucleons are found in the central part or nucleus of the atom.

(iii) The outermost shell of an atom is known as valence shell and the electrons present in the valence shell are known as valence electrons.

ICSE Class 9 Chemistry Question Papers with Answers

ICSE Class 9 Chemistry Sample Question Paper 1 with Answers

Max Marks : 80
[2 Hours]

General Instructions

• Answers to this Paper must be written on the paper provided separately.
• You will not be allowed to write during the first 15 minutes.
• This time is to be spent in reading the Question Paper.
• The time given at the head of this paper is the time allowed for writing the answers.
• Section I is compulsory. Attempt any four questions from Section II.
• The intended marks for questions or parts of questions are given in brackets [ ].

Section-I [40 Marks]
(Attempt all questions from this section)

Question 1.
(a) Fill in the blanks with the correct choice given in brackets. [5]
(i) In an ionic compound, the bond is formed due to of electrons. …………………… [sharing/transfer]
(ii) Zinc is reactive than aluminum …………………… [less/more]
(iii) The chemical reaction in which heat is absorbed is known as reaction ……………………. [endothermic/ exothermic]
(iv) The molecular formula of ammonium sulphate is …………………… [NH₄SO₄/(NH₄)₂SO₄]
(v) If an element has two electrons in its outermost shell, then it is likely to be …………………… [metallic/ non-metallic]
Answer:
(i) transfer
(ii) less
(iii) endothermic
(iv) (NH₄)2SO₄
(v) Metallic

(b) Choose the correct answer from the options given below : [5]
(i) The gas that causes the greenhouse effect:
(A) Oxygen
(B) Ammonia
(C) Methane
(D) Hydrogen Sulphide
Answer:
(C) Methane

(ii) According to the modem periodic law, the properties of elements are a periodic function of their :
(A) Atomic volume
(B) Atomic number
(C) Atomic weight
(D) Mass number
Answer:
(B) Atomic number

(iii) Which of the following has water of crystallization ?
(A) Potassium chloride
(B) Sodium chloride
(C) Sodium nitrate
(D) Washing soda crystals
Answer:
(D) Washing soda crystals

(iv) The gas which has a rotten egg smell is :
(A) Hydrogen sulphide
(B) Ammonia
(C) Sulphur dioxide
(D) Hydrogen chloride
Answer:
(A) Hydrogen sulphide

(v) The temperature of 0° Celcius on the Kelvin scale is equal to :
(A) – 273 K
(B) 273 K
(C) 0 K
(D) 100 K
Answer:
(B) 273 K

(c) Name the gas evolved in each of the following cases : [5]
(i) Copper carbonate is heated strongly.
(ii) Action of dilute hydrochloric acid on sodium sulphite.
(iii) Nitrogen combines with hydrogen.
(iv) Action of dilute sulphuric acid on sodium carbonate.
(v) Addition of sodium to cold water.
Answer:
(i) Carbon dioxide
(ii) Sulphur dioxide
(iii) Ammonia
(iv) Carbon dioxide
(v) Hydrogen

(d) Give a reason for each of the following : [5]
(i) Noble gases do not combine with other elements to form molecules.
(ii) Dilute nitric acid cannot be used in the preparation of hydrogen.
(iii) Hydrogen although lighter than air, is not collected by the downward displacement of air.
(iv) Anhydrous calcium chloride turris into a colourless solution when exposed to air.
(v) Metals form positive ions.
Answer:
(i) Noble gases have 2 electrons in their outermost shell that is completely filled and moreover, it is the maximum number of valence electrons their outer shell can hold hence, these are unreactive.

(ii) When metal reacts with water it produces hydrogen gas. Nitric acid is a very strong oxidizing agent and it oxidizes the hydrogen gas produced during the reaction of metal with water. Hence, dilute nitric acid cannot be used in the preparation of hydrogen.

(iii) Hydrogen gets oxidized when it is exposed to oxygen which makes it bum with a pale blue flame and the residue is water. This means that it mixes with oxygen. Downward displacement of air requires a gas that does not mix with air and is lighter than air. Hydrogen is lighter than air but mixes with air.

(iv) Calcium chloride is deliquescent. If exposed to air, it will absorb sufficient water from the air to allow it to dissolve. After a short while, instead of a white lump, a pool of clear liquid is formed.

(v) Ions are formed when an atom either loses or gains electron and gets charged accordingly. All metals have electrons in their outermost shell which can be easily lost.

(e) What do you observe when : [5]
(i) Iodine crystals are heated in a test tube ?
(ii) Iron nails are added to copper sulphate solution ?
(iii) Lead nitrate crystals are heated strongly ?
(iv) Ferric chloride crystals are exposed to atmosphere for some time ?
(v) Blue copper sulphate crystals are heated ?
Answer:
(i) When Iodine crystals are heated in a test tube, the van der Waals forces are easily overcome and the molecule breaks into gas phase. They sublime and form a purple coloured dense vapours.

(ii) When iron nails are added to copper sulphate the blue colour of the solution fades eventually and turns into light green due to the formation of ferrous sulphate.

(iii) When lead nitrate crystals are heated strongly, lead decomposes and leaves yellow fesidue of lead monoxide, brown gas nitrogen dioxide and colourless gas oxygen are evolved.

(iv) When ferric chloride crystals are heated hydrated hydrogen chloride is formed which is rarely observed in its natural form.

(v) The blue coloured copper sulphate crystals turn white due to the loss of water molecules. The formula of copper sulphate is CuSO₄.5H₂O. When copper sulphate is heated, it loses water molecules and hence it loses blue colour.

(f) (i) State Boyle’s law. [5]
(ii) What is standard temperature and pressure ?
(iii) Calculate the percentage of nitrogen in ammonium nitrate. [NH₄NO_s].
[N = 14, H = 1, O = 16]
Answer:
(i) As per Boyle’s law, the absolute pressure and the volume of a gas are inversely proportional at constant temperature.

(ii) Standard temperature is defined as equal to 0°C, 0°C = 273.15 K.
Standard Pressure is defined as 1 Atm, which is equal to 101. 3kPa or 760 mmHg.

(iii) Molecular mass of NH₄NO₃ = 23 + 16 + 1 = 40
In ammonium nitrate, there are 2 atoms of nitrogen
Hence, molecular mass = 2 x 40 = 80
Percentage of nitrogen

(g) (i) Balance each of the chemical equations given below : [5]
1. FeCl₃ + NH₄OH → NH₄Cl + Fe(OH)₃
2. KI + Cl₂ → KCl + I₂
Answer:
(i) (1) FeCl₃ + 3NH₄OH → 3NH₄Cl + Fe(OH)₃
(2) 2KI + Cl₂ → 2KCl + I₂

(ii) Identify the substance which matches the description given below :
1. White crystalline substance which sublimes on heating.
2. The gas which turns lime water milky but has no effect on potassium dichromate paper.
3. The metal that cannot displace hydrogen from dilute hydrochloric acid.
Answer:
(1) Iodine crystals
(2) CO₂
(3) Metals like Cu, Ag and Au are less reactive than hydrogen; hence these metals cannot displace hydrogen from dilute hydrochloric acid.

(h) Match Column A with Column B.

	Column A		Column B
(i)	Causes hardness in water	(A)	Calcium oxide
(ii)	Causes ozone depletion	(B)	Concentrated sulphuric acid
(iii)	Dehydrating agent	(C)	Magnesium bicarbonate
(iv)	Causes acid rain	(D)	Chlorofluorocarbon
(v)	Drying agent	(E)	Nitrogen dioxide

Answer:
(i) (C)
(ii) (D)
(iii) (B)
(iv) (E)
(v) (A)

Section – II [40 Marks]
(Attempt any four questions from this section)

Question 2.
(a) The formula of the chloride of a metal ‘M’ is MC12. State the formula of its : [3]
(i) Carbonate (ii) Nitrate (iii) Hydroxide
Answer:
(i) MCO
(ii)M(NO₃)₂
(iii) M(OH)₂

(b) Write balanced chemical equations for each of the following : [3]
(i) Reaction of iron with chlorine.
(ii) Addition of silver nitrate solution to sodium chloride solution.
(iii) Addition of zinc to sodium hydroxide solution.
Answer:
(i) When iron reacts with chlorine, toxic brown fumes are produced and crystals of iron chloride are formed.
2Fe + 3Cl₂ → 2FeCl₃
(ii) NaCl + AgNO_s → AgCl + NaNO₃
(iii) \(\mathrm{Zn}+2 \mathrm{NaOH} \stackrel{t^{\circ} \mathrm{C}}{\longrightarrow} \mathrm{Na}_{2} \mathrm{ZnO}_{2}+\mathrm{H}_{2}\)

(c) Draw the orbit structure for each of the following compounds : [4]
(i) Methane [H = 1, C = 6]
(ii) Megnesium chloride [Mg = 12, Cl = 17]
Answer:
(i) Orbit structure of methane

(ii) Orbit structure of magnesium chloride

The two electrons lost by a magnesium atom are gained by chlorine atoms to produce a magnesium ion and two chloride ions.

Question 3.
(a) (i) Name the industrial method for the production of hydrogen gas. [3]
(ii) Name the catalyst used in the above process.
(iii) Write the balanced chemical equation for the production of water gas.
Answer:
(i) Electrolysis of water is the industrial method used for the preparation of hydrogen gas.
(ii) Catalyst used in the above process is nickel.
(iii) 2H₂O → 2H₂ + O₂

(b) (i) What is meant by ‘Group’ in the periodic table ? [3]
(ii) Explain why the elements of the same group exhibit the same chemical behaviour.
(iii) In which group are the inert gases placed in the periodic table ?
Answer:
(i) Vertical columns in the periodic table are called Groups. The periodic table has eighteen vertical columns, comprising of groups (I to VIII and Zero). The groups are further divided into sub-groups thereby making a total of eighteen groups.
(ii) Elements of the same group exhibit same chemical behaviour because their atoms have the same number of electrons in the highest occupied energy level.
(iii) Elements of the Zero group, which is the 18th vertical column, are known as inert gases or noble gases.

(c) A part of the periodic table is shown below with one element missing : [4]

H							He
Li	Be	B	C	N	O	F	Ne
Na	Mg	Al	Si	–	s	Cl	Ar
K	Cl

(c) Based on the above table, answer the following questions :
(i) Name the element that has duplet structure.
(ii) Name the lightest alkali metal.
(iii) Name the halogen of period 2.
(iv) Identify the missing element.
Answer:
(i) Hydrogen and lithium have duplet structure.
(ii) Lightest alkali metal is lithium.
(iii) Fluorine is the halogen of period 2.
(iv) Missing element is phosphorus

Question 4.
(a) Calculate the volume of gas X at S.T.P. if it occupies 380 litres at ,300 K and 70 cm of mercury. [3]
(b) A gas occupies 70 litres at 27°C. [3]
What volume will it occupy at 273°C, pressure remaining constant ?
(c) Calculate the relative molecular mass of each of the following : [4]
(i) Ammonium dichromate [(NH₄)₂Cr₂O₇]
(ii) Hydrated copper sulphate [CuSO₄.5H₂O]
[H = 1, N = 14, O = 16, S = 32, Cr = 52, Cu = 64]
Answer:
(a) Let the volume at STP is V₁ = ?, V₂ = 380 litre
P₁ = 760 mm of Hg, P₂ = 70 cm of Hg
T₁= 273 K, T₂ = 300 K,

Question 5.
(a) (i) What do you understand by the term isotopes ? [3]
(ii) Why do isotopes of an element possess identical chemical properties ?
(iii) Name the isotope of hydrogen which does not have a neutron in it.
Answer:
(i) Isotopes are atoms of the same element having the same numbers of protons (atomic number), but different numbers of neutrons. They have same chemical properties due to the same electronic configuration but different physical properties.

(ii) Isotopes have same chemical properties due to the same electronic configuration but possess different physical properties.

(iii) ¹H, ²H, and ³H are all isotopes of hydrogen and is known as protium which has no neutron in it.

(b) State the type of covelent bonding in the following molecules : [3]
(i) Chlorine
(ii) Nitrogen
(iii) Oxygen
Answer:
(i) Chlorine molecule has a single covalent bond, as one pair of electrons is shared between the atoms.
(ii) Nitrogen has triple covalent bond in it, which is a combination of three single bonds.
(iii) Oxygen has double covalent bond present in it, as it is formed by sharing of two pair of electrons between two atoms.

(c) How would you distinguish between the following pairs of substances on the basis of the chemical tests given in brackets ? [4]
(i) Sodium chloride and potassium chloride (flame test)
(ii) Zinc carbonate and lead carbonate (dry heating)
Answer:
(i) When flame test is performed on sodium chloride, golden yellow colour is imparted to the flame and when seen through a blue glass yellow colour vanishes. When flame test is performed on potassium chloride, violet colour is observed with naked eyes and violet or pink colour is seen through a blue glass.

(ii) When zinc carbonate is dry heated it decomposes to give zinc oxide and yellow colour is seen when hot and white cold, while lead carbonate decomposes to give lead oxide and brown colour is seen when hot and yellow when cold.

Question 6.
(a) State if the solubility increases, decreases or remains the same with rise in temperature for each of the following compounds :  [3]
(i) Calcium sulphate
(ii) Potassium nitrate
(iii) Sodium chloride
Answer:
(a) Effect of solubility on various compounds when temperature remains constant:
(i) There is a decrease in solubility of calcium sulphate with further rise in temperature.
(ii) Potassium nitrate shows considerable increase in solubility with further rise in temperature.
(iii) Solubility of sodium chloride increases only a little, with increase in temperature.

(B) (i) What is the difference between temporary hard water and permanent hard water ? [3]
(ii) Write a balanced chemical equation for the removal of :
1. Permanent hardness
2. Temporary hardness
Answer:

Temporary hard water	Permanent hard water
Water that contains only hydrogen carbonates of calcium and magnesium is called temporary water.	Water containing sulphates and chlorides of magnesium and calcium is called permanent hard water.
Temporary hardness of water is removed by boiling, by addition of lime and by addition of washing soda.	To remove permanent hardness of water it is treated with a calculated quantity of soda ash.
Temporary hardness is called as carbonate or alkaline hardness.	It is also known as non-carbonate or non alkaline hardness.

(ii) 1. Permanent hardness :
MgSO₄ + Na₂CO₃ + Ca(OH)₂ → Mg(OH)₂ + CaCO₃ + Na₂SO₄
2. Temporary hardness :
Ca(HCO₃)₂ → CaCO₃ + H₂O + CO₂
2Al + Fe₂O₃ →Al₂O₃ + 2Fe

(c) Classify each of the following reactions as combination, decomposition, displacement or double displacement:  [4]
(i) 2Al + Fe₂O₃ → Al₂O₃ + 2Fe
(ii) 2KClO₃ → 2KCl + 3O₂
(iii) BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl
(iv) CaO + H₂O → Ca(OH)₂
Answer:
(i) This is an example of displacement reaction where a more reactive element i.e., aluminium displaces a less reactive element i.e., iron to form aluminium oxide.

(ii) 2KClO₃→ 2KCl + 3O₂ is an example of decomposition reaction where potassium chlorate decomposes to give potassium chloride and oxygen.

(iii) BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl is an example of double decomposition (precipitation reaction) where barium chloride and sodium sulphate react to form an insoluble white ppt. BaSO₄ and sodium chloride.

(iv) CaO + H₂O → Ca(OH)₂ is an example of combination reaction where calcium oxide and water combines to form calcium hydroxide.

Question 7.
Complete the following table : [6]

Element	Mass Number	Atomic Number	Number of Electrons	Number of  Protons	Number of Neutrons
Phosphorous	31	15	…………..	………….	………….
Potassium	………….	………….	19	………….	20

Answer:

Element	Mass Number	Atomic Number	Number of Electrons	Number of  Protons	Number of Neutrons
Phosphorous	31	15	15	15	16
Potassium	39	19	19	19	20

Number of electrons = Number of protons = Atomic number
Mass number = Number of protons + Number of neutrons

(b) Write the electronic configuration of the following :
(i) \({ }_{20}^{40} \mathrm{Ca}\)
(ii) \({ }_{16}^{32} \mathrm{~S}\)
Answer:
(i) Electronic configuration of Calcium is :
Is² 2s² 2p⁶ 3s² 3p⁶ 4s²
(ii) Electronic configuration of Sulphur is :
Is² 2s² 2p⁶ 3s² 3p⁴

(c) State the valency of the element having : [2]
(i) 6 electrons in the valence shell.
(ii) the electronic configuration of : 2, 3
Answer:
(i) The element which has 6 electrons in its valence shell is sulphur and its valency is 2.
(ii) The element whose electronic configuration is 2, 3 is Boron and its valency is 3.

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