Edexcel A-Level Chemistry Paper 2, June 2018: Question 2

3 marks · Easy difficulty · Short Open Response

Identify the process by which gaseous reactants attach to a catalytic surface and explain why a honeycomb structure is used in a car exhaust catalytic converter.

Practise this question

Question

Question 2 about how catalysts work. Part (a) is a multiple-choice question asking to identify the process by which gaseous reactants attach to the catalytic surface, with options A absorption, B activation, C adsorption, and D desorption. Part (b) asks to explain why a honeycomb structure is used in a car exhaust system, providing answer lines.
Question text

2 This question is about how catalysts work.

(a) Gaseous reactants attach to the catalytic surface by the process of

(1)

A absorption

B activation

C adsorption

D desorption

(b) Catalytic converters of car exhaust systems have internal honeycomb structures as shown.

Explain why the honeycomb structure is used in a car exhaust system.

(2)

(Total for Question 2 = 3 marks)

Mark scheme

Show the mark scheme Mark scheme for Question 2. Part (a) indicates that C is the correct answer (adsorption) with 1 mark. Part (b) awards 2 marks: one for mentioning an increased surface area or more active sites, and the second for noting that the honeycomb structure allows gases to flow through the exhaust.

Question

Acceptable Answer Mark

Number

2(a) The only correct answer is C (1)

A is incorrect because gaseous reactants attach only to the surface

B is incorrect because this happens after adsorption

D is incorrect because this is detachment of the products from the surface

Question

Acceptable Answer Additional guidance Mark

Number

2(b) An explanation that makes reference to the following: (2)

increase surface (area) / more active sites (1) Do not award aBsorption

Ignore reference to rate of reaction / remove

pollutants

(honeycomb structure) allows gases to flow

Do not award if comments are made that

through (the exhaust) (1)

refer to the structure acting like a filter for

the particulates or other substances

(Total for Question 2 = 3 marks)

How to answer it

Study Guide: How Catalysts Work & Catalytic Converters

What this question tests

This question assesses your understanding of heterogeneous catalysis mechanisms—specifically the stages of surface processes (adsorption)—and your ability to link macroscopic structural features (honeycomb designs) to molecular-level properties like surface area and gas flow dynamics.

Question 2 (a)

The Mechanism of Heterogeneous Catalysis

✅ Correct Answer

C: adsorption

Mark: 1 / 1

💡 Key Knowledge

  • Adsorption: Gaseous reactants bond weakly to the active sites on the surface of a solid catalyst.
  • Reaction: Bonds within reactants weaken and break, forming intermediates, followed by product formation.
  • Desorption: The newly formed products detach from the catalyst surface.

❌ Common Errors

  • Confusing absorption (entering the bulk material) with adsorption (sticking to the surface).
  • Selecting desorption prematurely; reactants must attach before they can react and detach as products.
Question 2 (b)

Explaining the Honeycomb Structure in Car Exhausts

✅ Correct Answer (2 Marks)

  1. It increases the surface area / provides more active sites for the reaction. (1 mark)
  2. It allows gases to flow through freely without creating back-pressure. (1 mark)
Total Marks: 2 / 2

🧠 Exam Technique & Phrasing

  • Use precise terminology: say "surface area" or "active sites". Avoid vague phrases like "makes it bigger".
  • State clearly that gases can pass through. Examiners specifically reward the idea of unobstructed flow through the channels.

❌ Examiner Pitfalls (Do Not Write)

  • Do not call it a filter: The honeycomb does not filter out particulates; it catalytically converts toxic gases into harmless ones.
  • Do not confuse spelling: writing "absorption" instead of "adsorption" will lose credit if mentioned elsewhere.

Topics

Physical Chemistry · Topic 9: Kinetics I

Question and mark scheme from the Edexcel A-Level Chemistry examination, Paper 2, June 2018. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.