ICSE Class 9 Chemistry Sample Question Paper 7 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