1. 1
   A technician is following the three stages of the contact process to manufacture sulfuric acid from sulfur. In Stage 1, sulfur is burned in oxygen. In Stage 2, the product reacts further with oxygen in a reversible reaction using a vanadium(V) oxide catalyst at approximately 450°C and atmospheric pressure. In Stage 3, the Stage 2 product reacts with water.

   (a)

   In Stage 1 of the contact process, sulfur is burned in oxygen. What is the product of this stage?

   [1 mark]

   • ASulfur trioxide, SO_3
   • BSulfur dioxide, SO_2
   • CSulfuric acid, H_2SO_4
   • DHydrogen sulfide, H_2S

   (b)

   What is the catalyst used in Stage 2 of the contact process?

   [1 mark]

   • AIron
   • BPlatinum
   • CVanadium(V) oxide
   • DNickel

   (c)

   Write the balanced symbol equation, including state symbols, for the reversible reaction that occurs in Stage 2 of the contact process, and name the product formed.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chemical plant operator is checking the operating conditions of a contact process unit. Stage 2 is run at atmospheric pressure rather than a high pressure, and the operator wants to understand why this choice is made, alongside checking the final Stage 3 reaction.

   (a)

   In Stage 3 of the contact process, sulfur trioxide reacts with water. What is the product of this reaction?

   [1 mark]

   • ASulfuric acid
   • BSulfur dioxide
   • CSulfurous acid gas
   • DSulfur and oxygen

   (b)

   Why is Stage 2 of the contact process run at atmospheric pressure rather than a high pressure, even though increasing pressure would increase the equilibrium yield of sulfur trioxide?

   [1 mark]

   • AHigh pressure would decrease the rate of reaction
   • BThe vanadium(V) oxide catalyst stops working above atmospheric pressure
   • CSulfur trioxide cannot form at any pressure above atmospheric
   • DThe yield of sulfur trioxide at atmospheric pressure is already high enough, so the extra cost and safety risk of high pressure is not worthwhile

   (c)

   Explain why a temperature of approximately 450°C, rather than a much higher temperature, is used for Stage 2, given that the forward reaction is exothermic.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student is writing a report on the industrial manufacture of sulfuric acid by the contact process, covering all three stages and explaining why the reversible Stage 2 reaction is carried out under carefully chosen conditions.

   (a)

   Describe the overall process by which sulfur is converted into sulfuric acid in the contact process, naming each stage's reactants and products in order.

   [3 marks]

   (b)

   Explain, using ideas about rate and equilibrium yield, why a catalyst and a moderate temperature of approximately 450°C are both used together in Stage 2, rather than using no catalyst at a much lower temperature.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A safety and cost review is being carried out on a sulfuric acid plant that uses the contact process, focusing on whether the chosen conditions for Stage 2 represent the best balance of yield, rate, cost and safety.

   (a)

   Discuss why atmospheric pressure, rather than a high pressure, is used in Stage 2 of the contact process, referring to the effect of pressure on both equilibrium yield and rate, as well as cost and safety.

   [6 marks]

   (b)

   Discuss the choice of approximately 450°C for Stage 2 of the contact process, referring to the effect of temperature on rate and equilibrium yield, and explain the overall benefit of using the vanadium(V) oxide catalyst at this temperature.

   [6 marks]

   Total for question 4: 12 marks

End of questions