Class 9 Chemistry Annual Exam Answer Key

ANNUAL EVALUATION 2024-25
CHEMISTRY ANSWER KEY

Section 1: Answer any 4 questions from 1 to 5. Each carries 1 score.

1. Which allotrope of carbon is known as bucky balls?

Fullerene (or Buckminsterfullerene)

2. Find the relation and fill up the following
Soda water : solvent – water
Atmospheric air : solvent - ......(a)......

(a) Nitrogen

3. Examine the following statement and correct the portion underlined, if necessary.
The catalyst used in the manufacture of sulphuric acid is MnO₂

The catalyst used in the manufacture of sulphuric acid is Vanadium pentoxide (V₂O₅).

4. The isotopes of hydrogen are protium, deuterium and tritium. Identify the isotope whose oxide is heavy water.

Deuterium (D or ²H)

5. Which is the main component of CNG and LNG?

Methane (CH₄)

Section 2: Answer any 4 questions from 6 to 10. Each carries 2 scores.

6. Write any two merits of using organic fertilizers.

Merits of organic fertilizers:

- Improves soil structure and water retention.

- Environmentally friendly and sustainable.

7. 96g of potassium nitrate is dissolved in 200g water at 30°C.
[Hint: This is the maximum amount of potassium nitrate that can be dissolved in water at this temperature]

a) Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature.
b) Solubility of potassium nitrate at 30°C = 48g/100g water (since 96g dissolves in 200g water).

8. Coal is formed as a result of the carbonisation of plant remains that lie buried in the soil for years.

a) Carbonisation is the slow process of conversion of plant remains into coal under high pressure and temperature.
b) Anthracite has the highest carbon content.

9. Hydrogen was discovered by Henry Cavendish, a British scientist.

a) In the preparation of hydrogen in the laboratory, the reactants used are zinc and dilute hydrochloric acid (HCl) or sulphuric acid (H₂SO₄).
b) Balloons filled with hydrogen rise up in the air because hydrogen is lighter than air (lower density).

10. The structure of an aromatic hydrocarbon is given.

a) Benzene
b) Molecular formula: C₆H₆

Section 3: Answer any 4 questions from 11 to 15. Each carries 3 scores.

11. Substances can be mixed together to prepare mixtures.

a) Chalk powder + water and Muddy water are suspensions.
b) Characteristics of suspension:

- Heterogeneous mixture with visible particles.

- Particles settle over time.

12. An acid and an alkali undergo neutralisation reaction to form salt and water.

a) Positive ion in Mg(OH)₂: Mg²⁺
b) Negative ion in HCl: Cl⁻; Basicity of HCl = 1 (monoprotic acid).
c) Salt formed: MgCl₂ (Magnesium chloride).

13. The ozone layer depletion is harmful to living things and environment. Chlorofluorocarbons cause the depletion of ozone layer.

a) Chlorofluorocarbons (CFCs) release chlorine radicals in the stratosphere, which break down ozone (O₃) into oxygen (O₂).
b) Correct statements:

- ii) Ozone is found more commonly in the stratosphere.

- iii) This is a greenhouse gas.

14. C₂H₂, A, C₆H₆, ... belong to the same homologous series.

a) Compound A: C₄H₄ (assuming linear progression in the series).
b) Structural formula: H-C≡C-H (Ethyne-like structure).
c) Homologous series: Alkynes (general formula CₙH₂ₙ₋₂).

15. Chlorine is a gas used for bleaching purposes. Bleaching action of chlorine takes place in the presence of moisture.

a) Unstable compound: Hypochlorous acid (HOCl).
b) Products: HCl (hydrochloric acid) and O (oxygen radical).
c) Bleaching powder is prepared by reacting chlorine gas (Cl₂) with dry slaked lime (Ca(OH)₂).

Section 4: Answer any 4 questions from 16 to 20. Each carries 4 scores.

16. Take 10mL of concentrated hydrochloric acid in one test tube and 10 mL of dilute hydrochloric acid in another test tube. Put 2g magnesium each in both test tubes.

a) Concentrated HCl reacts faster.
b) Concentration of reactants influences the rate.
c) Higher concentration increases collision frequency, speeding up the reaction.
d) Mg + 2HCl → MgCl₂ + H₂↑

17. The atoms of the elements X and Y have 3 shells each. (Symbols are not real). X and Y belong to group 2 and group 15 respectively.

a) Electron configuration of X (Group 2, 3 shells): 2, 8, 2 (e.g., Magnesium).
b) Element Y (Group 15) belongs to the Nitrogen family (Pnictogens).
c) Element Y has bigger atoms (higher atomic radius in Group 15 than Group 2 in the same period).
d) Noble gas in the same period: Neon (Ne) – 2, 8.

18. Carbon monoxide and carbon dioxide are two compounds formed by the combination of carbon and oxygen.

a) 2C + O₂ → 2CO
b) Carbon dioxide (CO₂) turns lime water milky.
c) Water gas: CO + H₂; Producer gas: CO + N₂.

19. Sulphur dioxide (SO₂) reacts with oxygen to form sulphur trioxide (SO₃).

a) 2SO₂ + O₂ → 2SO₃
b) 160g SO₃ (1:1 molar ratio; 128g SO₂ = 2 moles → 2 moles SO₃ = 160g).
c) Oxidation numbers:

- SO₂: S = +4

- SO₃: S = +6

20. The IUPAC name of an organic compound is cyclopentane.

a) Cyclopentane structure: Pentagon with 5 carbon atoms, each bonded to 2 hydrogens.
b) Molecular formula: C₅H₁₀
c) Open-chain hydrocarbon: Pentene (C₅H₁₀); IUPAC name: 1-Pentene.