ICSE Class 7 Chemistry Sample Paper with Solutions Set 01

Question 1
Choose the correct answer out of the four available choices given under each question. [15]

1. The _________ substances do not have their own definite shape and volume. [1 Mark]
(a) crystal
(b) Solid
(c) Liquid
(d) Gaseous

Answer: (d) Gaseous

Gaseous substances do not have a definite shape or volume and expand to fill their container.

Teacher's Note:
a) Solids have a definite shape and volume, while liquids have a definite volume but no definite shape.
b) Students must remember the general characteristics of the three states of matter regarding shape and volume.

2. Metals react with dilute acids to liberate _________ gas. [1 Mark]
(a) Sulphur
(b) Oxygen
(c) Hydrogen
(d) Chlorine

Answer: (c) Hydrogen

Reactive metals displace hydrogen from dilute acids to form a salt and hydrogen gas.

Teacher's Note:
a) This is a standard chemical property of metals reacting with dilute mineral acids like hydrochloric acid.
b) Do not confuse this with non-metal reactions which do not typically liberate hydrogen gas with dilute acids.

3. A solution which cannot dissolve more of solute at a given temperature is called _________. [1 Mark]
(a) Unsaturated solution
(b) Saturated solution
(c) True solution
(d) Colloid solution

Answer: (b) Saturated solution

A saturated solution is one that holds the maximum amount of solute possible at a given temperature.

Teacher's Note:
a) An unsaturated solution can dissolve more solute at the same temperature.
b) Always mention "at a given temperature" in the definition since solubility varies with temperature.

4. Which of the following is a property of carbon dioxide [1 Mark]
(a) Combustible, non-supporter of combustion
(b) Combustible, supporter of combustion
(c) Non-combustible, supporter of combustion
(d) Non-combustible, non-supporter of combustion

Answer: (d) Non-combustible, non-supporter of combustion

Carbon dioxide does not catch fire itself, nor does it help other substances burn.

Teacher's Note:
a) Because of this property, carbon dioxide is widely used as a fire extinguisher.
b) Oxygen is a supporter of combustion, whereas carbon dioxide is a non-supporter.

5. Phosphorus burns in oxygen to form [1 Mark]
(a) Phosphorus oxide
(b) Phosphorus dioxide
(c) Phosphorus tetroxide
(d) Phosphorus pentoxide

Answer: (d) Phosphorus pentoxide

When phosphorus burns in oxygen, it forms phosphorus pentoxide (\(P_4O_{10}\) or \(2P_2O_5\)).

Teacher's Note:
a) The chemical equation is \(P_4 + 5O_2 \rightarrow 2P_2O_5\).
b) Pay close attention to the prefixes indicating the number of oxygen atoms in oxide names.

6. In a _____________ reaction, two substances exchange their radicals and form a new substance. [1 Mark]
(a) Direct combination
(b) Decomposition
(c) Simple displacement
(d) Double displacement

Answer: (d) Double displacement

In a double displacement reaction, two reacting compounds exchange their positive and negative radicals.

Teacher's Note:
a) Direct combination involves two or more substances combining to form a single product.
b) Double displacement typically occurs between two aqueous ionic compounds.

7. Which method is based on the difference in weights of solid particles? [1 Mark]
(a) Filtration
(b) Sieving
(c) Handpicking
(d) Winnowing

Answer: (d) Winnowing

Winnowing separates heavier and lighter components of a mixture using wind or blowing air based on weight.

Teacher's Note:
a) Sieving and filtration rely on differences in particle size.
b) Handpicking relies on visual distinction, size, and shape.

8. Electrolysis of water is an example of __________ reaction. [1 Mark]
(a) Combination
(b) Decomposition
(c) Double decomposition
(d) Displacement

Answer: (b) Decomposition

Electrolysis of water breaks down a single compound (\(H_2O\)) into two or more elements using electrical energy.

Teacher's Note:
a) Reactions where a single reactant breaks down into simpler products are decomposition reactions.
b) Since electricity drives this decomposition, it is specifically called electrolytic decomposition.

9. Burning of magnesium is a [1 Mark]
(a) Permanent
(b) Irreversible
(c) Chemical
(d) All of the above

Answer: (d) All of the above

Burning of magnesium ribbon produces a new substance (magnesium oxide), and the change cannot be undone.

Teacher's Note:
a) All chemical changes are permanent and irreversible by physical means.
b) Students should check all given options before selecting "All of the above".

10. In a chemical equation, the total mass of the reactants is equal to [1 Mark]
(a) Total quantity of the reactants
(b) Physical state of the reactants
(c) Total mass of the products
(d) Total mass of the solution

Answer: (c) Total mass of the products

This illustrates the Law of Conservation of Mass, which states that mass is neither created nor destroyed in a chemical reaction.

Teacher's Note:
a) A balanced chemical equation obeys the Law of Conservation of Mass.
b) The total number of atoms of each element must also be equal on both sides.

11. Sodium chloride is a [1 Mark]
(a) Acid
(b) Base
(c) Salt
(d) Alkali

Answer: (c) Salt

Sodium chloride (\(NaCl\)) is an ionic compound formed by the neutralization reaction between an acid and a base.

Teacher's Note:
a) Salts consist of positive metal ions and negative non-metal radicals.
b) \(NaCl\) is commonly known as table salt.

12. The molecular formula of water is [1 Mark]
(a) OH
(b) \(H_2O$
(c) \(H_2O_2$
(d) \(HO_2

Answer: (b) \(H_2O$

Each water molecule consists of two hydrogen atoms bonded to one oxygen atom.

Teacher's Note:
a) \(H_2O_2\) is the formula for hydrogen peroxide, which is a different compound.
b) Always write subscripts correctly to indicate the exact atom ratio.

13. The main chemicals that cause acid rain are_____ [1 Mark]
(a) \(CO_2\) and \(SO_2$
(b) \(SO_2\) and \(NO_2$
(c) \(CO_2\) and \(NO_2$
(d) \(O_2\) and \(CO_2$

Answer: (b) \(SO_2\) and \(NO_2$

Sulphur dioxide and nitrogen dioxide dissolve in atmospheric moisture to form sulfuric and nitric acids.

Teacher's Note:
a) These gases are primarily released from industrial emissions and the burning of fossil fuels.
b) Carbon dioxide causes global warming, but sulphur dioxide and nitrogen dioxide are the primary culprits of acid rain.

14. The symbol for copper is [1 Mark]
(a) Co
(b) Cp
(c) Cu
(d) Cr

Answer: (c) Cu

The symbol Cu is derived from its Latin name, cuprum.

Teacher's Note:
a) "Co" is the symbol for cobalt, and "Cr" is the symbol for chromium.
b) Students must learn standard chemical symbols derived from both English and Latin names.

15. Rusting of iron is a ________ change. [1 Mark]
(a) Chemical
(b) Physical
(c) Periodic
(d) Fast

Answer: (a) Chemical

Rusting forms a completely new substance (hydrated iron oxide) with different properties.

Teacher's Note:
a) Rusting is a slow, irreversible chemical process requiring both oxygen and moisture.
b) Physical changes do not form new substances.

Question 2

(A) Give the chemical formula for the following: [5]
1. Caustic soda
2. Nitric acid
3. Lead nitrate
4. Blue vitriol
5. Vinegar

Answer:
1. Caustic soda: NaOH
2. Nitric acid: \(HNO_3$
3. Lead nitrate: \(Pb(NO_3)_2$
4. Blue vitriol: \(CuSO_4 \cdot 5H_2O$
5. Vinegar: \(CH_3COOH$

Teacher's Note:
a) Ensure correct valencies are crossed over when writing chemical formulas like lead nitrate.
b) Water of crystallization must be included in hydrated salts such as blue vitriol.

(B) Fill in the blanks and rewrite the sentences: [5]
1. Manganese dioxide acts as a _______ during the formation of oxygen.
2. On burning a candle, _________ and _________ are formed.
3. When ammonium chloride is dissolved in water, heat is _________.
4. A sublimable solid on heating turns into _________.
5. Adding salt to water increases the ________ point of water.

Answer:
1. Manganese dioxide acts as a catalyst during the formation of oxygen.
2. On burning a candle, carbon dioxide gas and water vapour are formed.
3. When ammonium chloride is dissolved in water, heat is absorbed.
4. A sublimable solid on heating turns into a gas.
5. Adding salt to water increases the boiling point of water.

Teacher's Note:
a) Dissolution of ammonium chloride is an endothermic process, hence heat is absorbed.
b) Adding impurities like salt elevates the boiling point of pure solvents.

Question 3

(A) State whether True or False. [5]
1. Marble is a hydrated calcium sulphate.
2. Oxygen burns in an atmosphere of acetylene producing very high temperatures which is used for welding and cutting metals.
3. Metals occur in nature in both free and combined states.
4. Rusting is a slow oxidation process in which iron slowly reacts with oxygen of the air in the presence of moisture.
5. Water freezing into ice is an example of chemical change.

Answer:
1. False. (Gypsum is hydrated calcium sulphate, whereas marble is calcium carbonate.)
2. True.
3. True.
4. True.
5. False. (Water freezing into ice is a physical change.)

Teacher's Note:
a) State clearly whether the statement is True or False; provide corrections for false statements for clarity.
b) Phase changes like freezing are physical because no new chemical substance is formed.

(B) Match the following: [5]

Answer:

Teacher's Note:
a) Ensure phase transitions are matched accurately with their correct scientific terms.
b) Z represents vapour, Y represents liquid, and X represents solid.

Question 4

(A) Write the valency and the symbols for the following elements: [5]
a. Oxygen
b. Sulphur
c. Bromine
d. Chlorine
e. Carbon

Answer:

Teacher's Note:
a) Valency is the combining capacity of an element.
b) Capitalization of symbols must be accurate (e.g., Cl for chlorine, not CL).

(B) Give the chemical name for the following: [5]
1. NaOH
2. KOH
3. \(NaHCO_3$
4. CaO
5. \(H_3PO_4$

Answer:
1. Sodium hydroxide
2. Potassium hydroxide
3. Sodium bicarbonate
4. Calcium oxide
5. Phosphoric acid

Teacher's Note:
a) Sodium bicarbonate is also commonly known as baking soda.
b) Calcium oxide is commonly referred to as quicklime.

Question 5

(A) Give reasons: [5]
1. Addition of curd to milk is a chemical change.
2. Burning of sulphur powder is a chemical change.

Answer:
1. A chemical change is permanent and irreversible with the formation of a new substance. When curd is added to milk, lactose in milk converts to lactic acid, forming a new substance with entirely different composition and properties. This cannot be reversed back into milk.
2. Burning of sulphur powder results in the formation of sulphur dioxide gas. This change is permanent and irreversible as sulphur dioxide cannot be converted back into sulphur powder under normal conditions, and its properties differ completely from sulphur.

Teacher's Note:
a) Emphasize the formation of a new substance with distinct properties in both explanations.
b) Mention that chemical changes cannot be reversed by simple physical methods.

(B) Explain the term catalyst and its types. [5]

Answer:
1. A catalyst is a substance that alters (increases or decreases) the rate of a chemical reaction without itself undergoing any permanent chemical change at the end of the reaction.
2. Types of catalysts:
- Positive catalyst: A catalyst that increases the speed of a chemical reaction (e.g., Manganese dioxide (\(MnO_2\)) in the decomposition of potassium chlorate).
- Negative catalyst: A catalyst that decreases or retards the rate of a chemical reaction (e.g., Phosphoric acid (\(H_3PO_4\)) in the decomposition of hydrogen peroxide).

Teacher's Note:
a) Clarify that a catalyst does not initiate a reaction; it only changes its speed.
b) Give proper chemical examples for positive and negative catalysts to score full marks.

Question 6

(A) Define: [5]
1. Chemical equation
2. Reactants
3. Products
4. Balanced equation
5. Catalyst

Answer:
1. Chemical equation: A shorthand symbolic representation of a chemical reaction using symbols and chemical formulas of the reactants and products.
2. Reactants: The starting substances that undergo a chemical change during a reaction.
3. Products: The new substances formed as a result of a chemical reaction.
4. Balanced equation: A chemical equation in which the number of atoms of each element on the reactant side is equal to the number of atoms of that same element on the product side.
5. Catalyst: A substance that alters the rate of a chemical reaction without being consumed or chemically altered itself at the end of the reaction.

Teacher's Note:
a) Definitions must be precise and incorporate scientific terminology.
b) Ensure balanced equations satisfy the Law of Conservation of Mass.

(B) Compare in tabular form properties of Solids, Liquids and Gases with respect to : [5]
(i) Shape
(ii) Volume
(iii) Compressibility
(iv) Diffusion
(v) Fluidity or Rigidity

Answer:

Teacher's Note:
a) Draw a clean table with distinct columns for properties, solids, liquids, and gases.
b) Cover all five points requested in the question to secure full marks.

Question 7

1. Define mixture. What are its types? [4]

Answer:
1. Mixture: A mixture is a substance containing two or more elements or compounds mixed together in any proportion, where each substance retains its individual properties.
2. Types of mixtures:
- Heterogeneous mixture: A mixture in which components are not uniformly distributed throughout its volume and can be easily seen separately (e.g., oil in water).
- Homogeneous mixture: A mixture in which components are uniformly distributed throughout its volume and cannot be seen separately (e.g., salt in water).

Teacher's Note:
a) Highlight that components in a mixture do not undergo any chemical reaction with each other.
b) Give clear examples for both homogeneous and heterogeneous mixtures.

2. Explain the term atomicity in detail. [3]

Answer:
1. Atomicity is defined as the total number of atoms constituting a single molecule of an element.
2. Based on atomicity, molecules are classified as:
- Monatomic: Containing only one atom (e.g., Zinc, \(Zn$).
- Diatomic: Containing two atoms of the same type (e.g., Hydrogen, \(H_2$).
- Triatomic: Containing three atoms of the same type (e.g., Ozone, \(O_3$).
- Polyatomic: Containing more than three atoms of the same type (e.g., Phosphorus, \(P_4$).

Teacher's Note:
a) State the definition clearly before classifying molecules based on atomicity.
b) Provide correct molecular formulas as examples for each category.

3. Give the differences between elements and compounds. [3]

Answer:

Teacher's Note:
a) Present differences in a clear tabular format for readability.
b) Emphasize that elements are pure substances containing identical atoms, while compounds contain fixed ratios of different atoms.