OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2024: Question 5

1 mark · Medium difficulty · Multiple Choice

Identify the pair of reagents that tests for both functional groups present in geraniol.

Practise this question

Question

Multiple choice question 5 showing the chemical structure of geraniol containing two carbon-carbon double bonds and an alcohol group (-OH). Below it, four pairs of reagents (A, B, C, D) are listed to identify the functional groups, with an answer box at the bottom.
Question text

5 Geraniol, shown below, is a component in many natural oils.

OH

Geraniol

Which pair of reagents identifies both functional groups in geraniol?

A Acidified dichromate(VI) and 2,4-dinitrophenylhydrazine.

B Bromine water and 2,4-dinitrophenylhydrazine.

C Bromine water and acidified dichromate(VI).

D Tollens’ reagent and aqueous silver nitrate in ethanol.

Your answer

[1]

Mark scheme

Show the mark scheme The mark scheme indicates that the correct answer for question 5 is C, awarding 1 mark.

5 C 1

How to answer it

Identifying Functional Groups in Geraniol

OCR A-Level Chemistry — Multiple Choice Question

What this question tests

This question assesses your ability to inspect an organic structure, correctly identify all present functional groups, and recall the specific chemical tests (reagents and observations) used to confirm their presence in AS/A-Level Organic Chemistry.

Question 5 Analysis

Identifying Reagents for Geraniol

✅ Correct Answer: C

Bromine water and acidified dichromate(VI).

Bromine water tests for the alkene (C=C) double bonds (decolourises from orange to colourless). Acidified potassium dichromate(VI) tests for the primary alcohol (-OH) group (turns from orange to green on heating).

💡 Key Knowledge

  • Geraniol structure analysis: Contains two C=C alkene double bonds and one primary alcohol ( -OH ) group. It does not contain a carbonyl group (aldehyde or ketone).
  • Alkene test: Bromine water ( Br₂(aq) ) goes from orange to colourless.
  • Alcohol test: Acidified K₂Cr₂O₇ / H⁺ goes from orange to green for primary and secondary alcohols.

🧠 Exam Technique

Deconstruct molecules systematically before looking at options. Cover up the multiple-choice list and write down every functional group you see: here you have C=C and -OH . Immediately eliminate options containing carbonyl tests like 2,4-DNP or Tollens' reagent.

❌ Common Errors

  • Choosing options with 2,4-DNP (Options A and B) because students mistake complex organic structures for containing hidden aldehydes or ketones.
  • Confusing alcohol oxidising agents with halogenoalkane tests (aqueous silver nitrate in ethanol, used in Option D).
Mark allocation: [1 mark] awarded for selecting option C.

Topics

Module 4: Core organic chemistry · Module 6: Organic chemistry and analysis · 4.1 Basic concepts and hydrocarbons · 4.2 Alcohols, haloalkanes and analysis · 6.3 Analysis

Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.