Chemistry Paper 2 (SC),2019

Question 4

The following reaction scheme is an illustration of the contact process. Study the scheme and answer the questions that follow.
1. Name X and Y.
2. Write a balanced chemical equation for each of the processes I, II, III and IV.
3. Name the catalyst used in process II.
4. Using Le Chatelier’s principle, explain briefly why increasing the temperature would not favour the reaction in II.
5. State two uses of SO₂
[12 marks]
Consider the following reaction equation:
2H_2(g) + O_2(g) → 2H₂O_(g).
Calculate the volume of unused oxygen gas when 40 cm³ of hydrogen gas is sparked with 30 cm³ of oxygen gas.

[3 marks]

Calcium carbonate of mass 1.0 g was heated until there was no further change.
1. Write an equation for the reaction which took place.
2. Calculate the mass of the residue.
3. Calculate the volume of the gas evolved at s.t.p.
4. What would be the volume of the gas measured at 15 ℃ and 760 mm Hg? [C= 12.0, O = 16.0, Ca = 40.0, molar volume of a gas at s.t.p. = 22.4 dm³]

Observation

This question was well attempted, and performance of the candidates was good.

In part (a), majority of the candidates di splayed satisfactorily knowledge of the contact process and the appropriate equations for the different stages involved as well as the catalyst for the reaction.

In part (b), majority of the candidates were able to calculate the reacting volume and mass of the residue correctly, but could not satisfactorily convert the volume of gas using the general gas equation.

The expected answers include:

1. X - oxygen (1) Do not accept air
  Y - sulphur (1)
  (2 marks)
2. 1. S_(s) + O_2(g) ⟶ SO_2(g) (1)
  2. 2SO_2(g) + O_2(g) ⇌ 2SO_3(g) (2)
  3. SO_3(g) + H₂SO_4(aq) ⟶ H₂S₂O_7(l) (1)
  4. H₂S₂O_7(l) + H₂O_(l) ⟶ 2H₂SO_4(aq) (2)
3. Vanadium (V) oxide (1)
4. It is because the reaction is exothermic (1)
5. - In bleaching wood pulp, wool silk, hay
  - as germicide and fumigant/ disinfectant
  - as refrigerant / refrigerating gas/coolant
  - as preservative for grains and fruits
  - manufacture of H₂SO₄
  - as a reducing agent in metallurgy
  - for dichlorination

Chemistry Paper 2 (SCHOOL CANDIDATES) 2019

Question 4

Observation