AQA A-Level Chemistry Paper 3, 2023: Question 26

1 mark · Easy difficulty · Multiple Choice

Reaction Steps and Reagents This question involves identifying the correct reagent and condition for a specific step in a reaction scheme, focusing on the transformation of functional groups and conditions required for each step.

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Question

AQA A-Level Chemistry Paper 3, 2023: Question 26
Question text

26 Consider this reaction scheme.

Which step is shown with a correct reagent and a correct condition?

[1 mark]

A Step 1 HCN dissolved in water

B Step 2 KOH dissolved in warm water

C Step 4 CH3OH with an alkaline catalyst

D Step 5 H2 with a nickel catalyst

Mark scheme

Show the mark scheme Mark scheme for AQA A-Level Chemistry Paper 3, 2023: Question 26

26 D 1 (AO3) Step 5 H2 with a nickel catalyst

How to answer it

Analysis of Reaction Scheme

Question

Which step is shown with a correct reagent and a correct condition?

  • A: Step 1: HCN dissolved in water
  • B: Step 2: KOH dissolved in warm water
  • C: Step 4: CH3OH with an alkaline catalyst
  • D: Step 5: H2 with a nickel catalyst

Correct Answer: D

The correct step is Step 5 , where hydrogen gas (H2) is used with a nickel catalyst to hydrogenate a carbon-carbon double bond, forming a single bond.

Teacher Tip: Hydrogenation reactions often involve a transition metal catalyst such as nickel. Recognising this is essential for understanding industrial processes like margarine production.

Explanation of Other Options

  • A: HCN dissolved in water is a plausible reagent for a cyanohydrin formation, but it does not match the conditions described in the reaction scheme.
  • B: KOH dissolved in warm water is commonly used for elimination reactions, but this does not apply to the reaction in Step 2.
  • C: CH3OH with an alkaline catalyst is used for transesterification, which is unrelated to the reactions shown in Step 4.

Step-by-Step Process

Step 5: The double bond is hydrogenated using H2 gas and a nickel catalyst. This reaction converts the alkene into an alkane, finalising the reaction sequence.

Final Answer

The correct answer is:

D: Step 5: H2 with a nickel catalyst

Topics

Organic Chemistry · 3.3.14 Organic Synthesis

Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.