ICSE Class 9 Chemistry Sample Question Paper 6 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