Non Metals And Their Compounds | Competence Based Questions With Answers | Form Four

 

FORM FOUR CHEMISTRY: NON-METALS AND THEIR COMPOUNDS

15 Competence-Based Questions with Answers

1. Chlorine is widely used in the treatment of drinking water.

(a) Explain why chlorine is added to drinking water.
(b) Mention one disadvantage of using excess chlorine in water.

Answer:
(a) Chlorine is added to kill harmful microorganisms such as bacteria and viruses.
(b) Excess chlorine can give water an unpleasant taste and may form harmful compounds.

2. A student passes chlorine gas through moist blue litmus paper.

What observations would you expect?

Answer:
The blue litmus paper first turns red and then becomes bleached/white.

3. Hydrogen chloride gas is prepared in the laboratory by reacting sodium chloride with concentrated sulphuric acid.

(a) Write the balanced chemical equation.
(b) Why is the gas not collected over water?

Answer:
(a)
NaCl + H₂SO₄ → NaHSO₄ + HCl

(b) Hydrogen chloride is highly soluble in water, so it cannot be collected over water.

4. Carbon dioxide is produced when calcium carbonate reacts with dilute hydrochloric acid.

(a) Write the balanced equation.
(b) State one test for carbon dioxide.

Answer:
(a)
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

(b) Bubble the gas through limewater. Limewater turns milky.

5. A farmer discovers that the soil on his farm is too acidic. Explain how a compound of a non-metal can be used to help solve this problem.

Answer:
Calcium carbonate can be added to the soil. It reacts with acids and neutralizes the acidity, raising the soil pH.

6. Sulphur dioxide is released into the atmosphere from industries and burning fuels.

(a) State the environmental problem associated with sulphur dioxide.
(b) Explain how it occurs.

Answer:
(a) It contributes to acid rain.
(b) Sulphur dioxide reacts with oxygen and water in the atmosphere to form acidic substances such as sulphuric acid.

7. A student burns sulphur in air and collects the gas produced.

(a) Name the gas formed.
(b) Give one physical property of the gas.

Answer:
(a) Sulphur dioxide (SO₂).
(b) It is a colourless gas with a choking/pungent smell.

8. Ammonia is an important compound of nitrogen used in agriculture.

(a) Why is ammonia important to farmers?
(b) Give one fertilizer made from ammonia.

Answer:
(a) It is used to manufacture nitrogen fertilizers that supply nitrogen needed for plant growth.
(b) Ammonium nitrate / ammonium sulphate.

9. A student accidentally smells ammonia directly from a reagent bottle.

What is the correct laboratory practice that should have been followed?

Answer:
The student should not smell the gas directly. If instructed to identify the smell, the gas should be gently wafted towards the nose.

10. Nitrogen gas makes up a large proportion of air, but it does not readily support burning.

Explain why nitrogen is useful in food packaging.

Answer:
Nitrogen is relatively unreactive and does not readily react with food. It reduces oxidation and helps preserve food.

11. A candle is placed inside a container containing carbon dioxide. The flame goes out.

(a) Explain the observation.
(b) Give one use of this property of carbon dioxide.

Answer:
(a) Carbon dioxide does not support combustion and displaces oxygen around the flame.
(b) It is used in fire extinguishers.

12. During photosynthesis, green plants use carbon dioxide.

(a) Write the word equation for photosynthesis.
(b) Explain why carbon dioxide is important to plants.

Answer:
(a)
Carbon dioxide + Water → Glucose + Oxygen
(in the presence of light and chlorophyll)

(b) Carbon dioxide provides carbon used by plants to manufacture glucose.

13. A student adds dilute hydrochloric acid to a solution containing silver nitrate and observes a white precipitate.

(a) Name the precipitate formed.
(b) Write the ionic equation.

Answer:
(a) Silver chloride.
(b)
Ag⁺(aq) + Cl⁻(aq) → AgCl(s)

14. Hydrogen is considered a useful fuel because it produces water when it burns.

(a) Write the balanced equation for the combustion of hydrogen.
(b) State one advantage of hydrogen as a fuel.

Answer:
(a)
2H₂ + O₂ → 2H₂O

(b) Its combustion produces water and does not directly produce carbon dioxide.

15. A school laboratory has bottles labelled CO₂, H₂, O₂ and Cl₂, but the labels have fallen off. Suggest suitable tests that can be used to identify the gases.

Answer:

• CO₂: Turns limewater milky.
• H₂: Burns with a characteristic “pop” sound when tested carefully with a lighted splint.
• O₂: Relights a glowing splint.
• Cl₂: Bleaches moist litmus paper.