ICSE Class 7 Chemistry Sample Paper with Solutions Set 03

Question 1

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

1. _________are used for dyeing and colouring clothes. [1 Mark]
(a) Animal extracts
(b) Plant extracts
(c) Fossil fuels
(d) Salts

Answer: (b) Plant extracts

Plant extracts are used for dyeing and colouring clothes.

Teacher's Note:
a) Plant extracts contain natural coloring pigments used in various applications.
b) Students must remember that natural dyes are often obtained from botanical sources.

2. An evaporating dish is made of _______. [1 Mark]
(a) Porcelain
(b) Steel
(c) Aluminium
(d) Wood

Answer: (a) Porcelain

An evaporating dish is made of porcelain.

Teacher's Note:
a) Porcelain is chosen because it can withstand high temperatures during heating.
b) Do not confuse porcelain laboratory apparatus with metals that react with hot liquids.

3. Bronze is an alloy of ________. [1 Mark]
(a) Copper and tin
(b) Copper and silver
(c) Copper and nickel
(d) Copper and aluminium

Answer: (a) Copper and tin

Bronze is an alloy of copper and tin.

Teacher's Note:
a) Alloys are homogeneous mixtures of metals or a metal and a non-metal.
b) A common mistake is confusing bronze (copper and tin) with brass (copper and zinc).

4. Which of the following is volatile in nature [1 Mark]
(a) Common salt
(b) Petrol
(c) Water
(d) Milk

Answer: (b) Petrol

Petrol is volatile in nature.

Teacher's Note:
a) Volatile substances evaporate quickly at room temperature.
b) Students should note that petrol has a low boiling point and high vapor pressure.

5. Burning of fuels releases ______ in the atmosphere. [1 Mark]
(a) Carbon dioxide and water vapour
(b) Oxygen and water vapour
(c) Sulphur dioxide and water vapour
(d) Carbon monoxide and water vapour

Answer: (a) Carbon dioxide and water vapour

Burning of fuels releases carbon dioxide and water vapour in the atmosphere.

Teacher's Note:
a) Complete combustion of hydrocarbon fuels produces carbon dioxide and water vapor.
b) Always check if the question implies complete or incomplete combustion.

6. Balancing chemical equation is based on [1 Mark]
(a) Law of conservation of mass
(b) Mass of reactant and product
(c) Symbols and formulae
(d) None of the above

Answer: (a) Law of conservation of mass

Balancing chemical equation is based on Law of conservation of mass.

Teacher's Note:
a) The law states that mass can neither be created nor destroyed in a chemical reaction.
b) Ensure number of atoms of each element is equal on both reactant and product sides.

7. Nuts contain ______. [1 Mark]
(a) Carbohydrates
(b) Proteins
(c) Fats
(d) Methane

Answer: (c) Fats

Nuts contain Fats.

Teacher's Note:
a) Nuts are rich sources of dietary fats and oils along with proteins.
b) Read nutritional components carefully when classifying food items.

8. A fuel when used releases least amount of pollutants in the air. [1 Mark]
(a) Sulphur dioxide
(b) chlorofluorocarbon
(c) smoke
(d) CNG

Answer: (d) CNG

CNG releases least amount of pollutants in the air.

Teacher's Note:
a) Compressed Natural Gas (CNG) burns more cleanly than petrol or diesel.
b) It is considered an eco-friendly alternative fuel for vehicles.

9. Which of the following is used in advertising signboards? [1 Mark]
(a) Argon
(b) Krypton
(c) Xenon
(d) Helium

Answer: (d) Helium
(Note: The official key lists (d) Helium, though Neon is standard for red glow; following key verbatim.)

Helium is used in advertising signboards.

Teacher's Note:
a) Inert gases glow when an electric current is passed through them under low pressure.
b) The official key lists Helium; note that Neon is more typically cited for bright orange-red advertising signs.

10. ________ is hydrated calcium sulphate. [1 Mark]
(a) Marble
(b) Talc
(c) Gypsum
(d) Coal

Answer: (c) Gypsum

Gypsum is hydrated calcium sulphate.

Teacher's Note:
a) The chemical formula for gypsum is CaSO₄.2H₂O.
b) Distinguish clearly between anhydrous and hydrated forms of calcium sulphate.

11. Which of the following involves a change from the solid state directly to the gaseous state? [1 Mark]
(a) Evaporation
(b) Sublimation
(c) Condensation
(d) Solidification

Answer: (b) Sublimation

Sublimation involves a change from the solid state directly to the gaseous state.

Teacher's Note:
a) Camphor, dry ice, and ammonium chloride are common examples that undergo sublimation.
b) Remember that no liquid state is formed during the sublimation process.

12. Petroleum is refined using ______. [1 Mark]
(a) Filtration
(b) Sedimentation
(c) Distillation
(d) Evaporation

Answer: (c) Distillation

Petroleum is refined using distillation.

Teacher's Note:
a) Fractional distillation separates crude oil components based on their boiling points.
b) Do not confuse fractional distillation with simple filtration methods.

13. The symbol of mercury is _______. [1 Mark]
(a) Me
(b) Hg
(c) Mg
(d) He

Answer: (b) Hg

The symbol of mercury is Hg.

Teacher's Note:
a) The symbol Hg is derived from its Greek name hydrargyrum.
b) Avoid mixing up Hg (mercury) with Mg (magnesium) or He (helium).

14. The molecular formula of hydrogen is ________. [1 Mark]
(a) H₁
(b) H₂
(c) H₃
(d) H₄

Answer: (b) H₂

The molecular formula of hydrogen is H₂.

Teacher's Note:
a) Hydrogen is a diatomic molecule existing naturally as H₂.
b) Always write the correct subscript to represent diatomic elemental gases.

15. The process by which oxidation of food in our body take place is [1 Mark]
(a) Photosynthesis
(b) Respiration
(c) Decomposition
(d) Combustion

Answer: (b) Respiration

The process by which oxidation of food in our body take place is respiration.

Teacher's Note:
a) Cellular respiration breaks down glucose to release energy within living cells.
b) Respiration is a slow oxidation process unlike rapid combustion.

Question 2

(A) Give a scientific word for the following: [5 Marks]

1. A gas liberated when dilute acids react with metals. [1 Mark]

Answer: Hydrogen gas.

Teacher's Note:
a) Active metals react with dilute acids to evolve hydrogen gas.
b) The pop sound test confirms the presence of hydrogen gas.

2. An alloy of copper, tin and zinc. [1 Mark]

Answer: Bronze.

Teacher's Note:
a) Bronze is primarily copper and tin, often containing minor amounts of zinc.
b) Ensure accurate recall of alloy constituents.

3. A substance made by fusing sand, soda and gravel. [1 Mark]

Answer: Glass.

Teacher's Note:
a) Glass is an amorphous solid formed by fusing silica, sodium carbonate, and limestone or gravel.
b) It is considered a supercooled liquid rather than a true crystalline solid.

4. A substance used to speed up or slow down the chemical reactions without taking part in the reaction. [1 Mark]

Answer: Catalyst.

Teacher's Note:
a) Catalysts alter the rate of a chemical reaction without undergoing permanent chemical change.
b) Positive catalysts increase the reaction rate, while negative catalysts decrease it.

5. Molecules of an element containing three atoms of the same type. [1 Mark]

Answer: Triatomic molecules.

Teacher's Note:
a) Ozone (O₃) is a classic example of a triatomic elemental molecule.
b) Atomicity refers to the total number of atoms present in a single molecule of an element.

(B) Fill in the blanks and rewrite the sentences: [5 Marks]

1. Latin name for copper is ______. [1 Mark]

Answer: Cuprum.

Teacher's Note:
a) Chemical symbols are often derived from Latin names of elements.
b) The symbol Cu comes from Cuprum.

2. Oxygen occupies about _________ of air by volume. [1 Mark]

Answer: 21%.

Teacher's Note:
a) Air is a mixture containing approximately 78% nitrogen and 21% oxygen.
b) Students must specify percentages by volume when describing atmospheric composition.

3. _________ is used in observation balloons. [1 Mark]

Answer: Helium.

Teacher's Note:
a) Helium is light and non-flammable, making it ideal for weather and observation balloons.
b) Hydrogen is lighter but highly flammable, so helium is preferred for safety.

4. _________ is used to prepare solutions for medicinal purposes, laboratories and car batteries. [1 Mark]

Answer: Distillation (Note: Distilled water is implied for preparing solutions).

Teacher's Note:
a) Distilled water is free from dissolved mineral impurities.
b) Pure water is essential in laboratories and storage batteries to prevent unwanted side reactions.

5. Plaster of Paris is ________. [1 Mark]

Answer: Calcium sulphate hemihydrate (Note: The official key answers "calcium sulphate".)

Teacher's Note:
a) Plaster of Paris has the chemical formula CaSO₄.½H₂O.
b) The official key mentions calcium sulphate; specifying hemihydrate is chemically precise.

Question 3

(A) Match the item in Column A with the appropriate item in Column B. [5 Marks]

Teacher's Note:
a) Match environmental and chemical phenomena accurately with their correct scientific causes or substances.
b) Manganese dioxide acts as a catalyst in the laboratory preparation of oxygen.

(B) Give uses of following inert gases [5 Marks]

Answer:
1. Helium (He): It is the second lightest element known to man. It is used for filling up balloons.
2. Argon (Ar): It is used in electric bulbs.
3. Neon (Ne): It is used in advertising sign boards.
4. Radon (Rn): It is the only radioactive inert gas used for cancer treatment.
5. Xenon (Xe) and Krypton (Kr): Both are used in photography.

Teacher's Note:
a) Noble gases are unreactive due to their stable electronic configurations.
b) Memorize specific industrial and medical applications for each inert gas.

Question 4

(A) Classify the following elements as metals , non-metals and metalloids [5 Marks]

Teacher's Note:
a) Elements are classified based on physical and chemical properties into metals, non-metals, and metalloids.
b) Metalloids possess properties intermediate between metals and non-metals.

(B) Define the following: [5 Marks]

1. Homogeneous mixtures [1 Mark]

Answer: A mixture in which the components or constituents are uniformly distributed throughout its volume is called homogeneous mixtures.

Teacher's Note:
a) Solutions are typical examples of homogeneous mixtures.
b) The composition is uniform throughout the entire sample.

2. Rusting of iron [1 Mark]

Answer: Rusting is a slow oxidation process in which iron slowly reacts with oxygen of the air in the presence of moisture and produces a flaky brown substance called rust.
\( 4Fe + 3O_{2} + xH_{2}O \rightarrow 2Fe_{2}O_{3} \cdot xH_{2}O \)
Rust is hydrated ferric oxide, which forms a reddish brown coating over iron. Rusting corrodes iron, weakens iron structure, and thus causes economic loss.

Teacher's Note:
a) Both oxygen and moisture are essential conditions for rusting to occur.
b) Mention the chemical formula for rust to score full marks.

3. Nitrogen fixation [1 Mark]

Answer: The phenomenon by which nitrogen is converted into nitrates and nitrites and get fixed in the soil or directly due to some bacterial action is known as nitrogen fixation.

Teacher's Note:
a) Atmospheric nitrogen cannot be utilized directly by most plants.
b) Rhizobium bacteria in root nodules play a vital role in biological nitrogen fixation.

4. Atomicity [1 Mark]

Answer: The number of atoms of an element which join to form a molecule of that element is known as the atomicity of that molecule.

Teacher's Note:
a) Noble gases have an atomicity of one (monoatomic).
b) Oxygen gas has an atomicity of two (diatomic).

5. Polyatomic molecules [1 Mark]

Answer: Polyatomic molecules of an element contain more than three atoms of the same type.

Teacher's Note:
a) Phosphorus (P₄) and sulfur (S₈) are examples of polyatomic molecules.
b) Clearly distinguish between diatomic, triatomic, and polyatomic molecules.

Question 5

(A) Give the chemical formulae for the following: [5 Marks]

1. Hydrochloric acid [1 Mark]

Answer: HCl

Teacher's Note:
a) Hydrochloric acid is a strong mineral acid.
b) Ensure correct capitalization of elemental symbols.

2. Potassium hydroxide [1 Mark]

Answer: KOH

Teacher's Note:
a) Potassium hydroxide is a strong caustic alkali.
b) Balance valencies when writing chemical formulas.

3. Sulphuric acid [1 Mark]

Answer: H₂SO₄

Teacher's Note:
a) Known as the king of chemicals, sulphuric acid is widely used in industries.
b) Use proper subscript notation for hydrogen and oxygen atoms.

4. Aluminium sulphate [1 Mark]

Answer: Al₂(SO₄)₃

Teacher's Note:
a) Cross-valency method gives the correct formula for aluminium sulphate.
b) The sulfate radical is enclosed in parentheses with a subscript of 3.

5. Magnesium oxide [1 Mark]

Answer: MgO

Teacher's Note:
a) Magnesium has a valency of +2 and oxygen -2, combining in a 1:1 ratio.
b) Magnesium oxide forms a basic white ash when magnesium ribbon burns in air.

(B) State five characteristics of chemical reactions [5 Marks]

Answer:
1. Change of colour: In some chemical reactions, change of colour takes place when reactants form the products. (Example: When green-coloured copper carbonate is heated, it turns into black-coloured copper oxide: CuCO₃ → CuO + CO₂).
2. Evolution of a gas: In some reactions, one of the products is a gas, which can be recognised by effervescence, smell or colour. (Example: Reaction of dilute sulphuric acid with iron flakes evolves hydrogen gas: Fe + H₂SO₄ → FeSO₄ + H₂ ↑).
3. Formation of a precipitate: In certain chemical reactions, an insoluble solid substance is formed called precipitate. (Example: Reaction of iron sulphate with sodium hydroxide forms a dirty green precipitate of iron(II) hydroxide: FeSO₄ + 2NaOH → Na₂SO₄ + Fe(OH)₂ ↓).
4. Change of state: In certain chemical reactions, a change of state is observed from solid/liquid to gas or vice versa. (Example: Burning of hydrogen gas in oxygen produces liquid water).
5. Change of smell: During some chemical reactions, a strong or characteristic smell is noticed. (Example: Heating ammonium chloride with sodium hydroxide releases ammonia gas with a pungent smell).

Teacher's Note:
a) Chemical reactions are characterized by observable macroscopic changes.
b) Giving chemical equations along with characteristics ensures full credit.

Question 6

(A) State whether True or False. [5 Marks]

1. Milk is a mixture. [1 Mark]

Answer: True.

Teacher's Note:
a) Milk is a colloidal mixture of fat globules dispersed in water.
b) Its components can be separated by physical methods like centrifugation.

2. No new substance is formed during chemical change. [1 Mark]

Answer: False. (New substance is formed during chemical change.)

Teacher's Note:
a) Chemical changes always result in the formation of one or more new substances.
b) Physical changes do not produce new substances.

3. Sulphuric acid is a weak acid. [1 Mark]

Answer: False. (Sulphuric acid is a strong acid.)

Teacher's Note:
a) Sulphuric acid ionizes almost completely in aqueous solution.
b) Organic acids like acetic acid are typically weak acids.

4. Black residue is formed when sugar is heated. [1 Mark]

Answer: True.

Teacher's Note:
a) Heating sugar dehydrates it, leaving behind a black carbon residue.
b) This is an example of thermal decomposition.

5. A conical flask is used for storing and mixing liquids. [1 Mark]

Answer: True.

Teacher's Note:
a) Conical flasks are designed for easy swirling of liquids without spilling.
b) They are standard laboratory glassware for titrations and mixing.

(B) Match the apparatus with its correct use. [5 Marks]

Teacher's Note:
a) Laboratory equipment must be correctly matched with its primary function.
b) Wire gauze distributes heat evenly to prevent thermal shock in glassware.

Question 7

1. Distinguish between metal and non-metal [4 Marks]

Teacher's Note:
a) Properties of elements determine their classification into metals and non-metals.
b) Always mention exceptions like mercury for physical state and graphite for electrical conductivity.

2. Distinguish between pure substance and mixture. [3 Marks]

Teacher's Note:
a) Pure substances consist of only one type of atom or molecule with fixed composition.
b) Mixtures are physically combined and retain the individual properties of their components.

3. Distinguish between physical and chemical changes. [3 Marks]

Teacher's Note:
a) In physical changes, only physical properties like state or shape change.
b) In chemical changes, internal chemical composition changes completely to form new products.