OCR A-Level Chemistry Synthesis and analytical techniques (02), November 2021: Question 15

1 mark · Medium difficulty · Multiple Choice

Identify which of the given compounds (phenol, benzoic acid, and phenylmethanol bromide derivative) react with aqueous sodium hydroxide.

Practise this question

Question

Multiple choice question showing a table with three compounds: compound 1 is phenol (a benzene ring attached to an OH group), compound 2 is benzoic acid (a benzene ring attached to a COOH group), and compound 3 is (bromomethyl)benzene (a benzene ring attached to a CH2Br group). Below the table are four options A, B, C, and D representing combinations of these compounds that react with NaOH(aq).
Question text

15 Compounds 1, 2 and 3 are heated with NaOH(aq).

Which compound(s) react(s)?

OH

COOH

CH2Br

A 1, 2 and 3

B Only 1 and 2

C Only 2 and 3

D Only 1

Your answer

[1]

Mark scheme

Show the mark scheme The mark scheme indicates that the correct answer is A, worth 1 mark, corresponding to AO1.2.

15 A 1 AO1.2

Total 15

How to answer it

Reactivity of Aromatic Compounds with Aqueous Sodium Hydroxide

What this question tests

This question assesses your knowledge of organic functional group chemistry, specifically the acidic properties of phenols and carboxylic acids, and the nucleophilic substitution reactions of halogenoarenes/halogenoalkanes when heated with aqueous alkali ( NaOH(aq) ).

Question 15

Analysis of Compounds 1, 2, and 3

✅ Correct Answer

Option A: 1, 2 and 3

All three compounds react when heated with NaOH(aq) via distinct chemical pathways.

💡 Key Knowledge

  • Compound 1 (Phenol): Reacts with NaOH(aq) in an acid-base neutralization reaction to form a soluble sodium phenoxide salt and water.
  • Compound 2 (Benzoic acid): Reacts with NaOH(aq) because carboxylic acids are strong enough acids to react with alkalis, forming sodium benzoate and water.
  • Compound 3 (Bromomethylbenzene / Benzyl bromide): Undergoes nucleophilic substitution where the primary aliphatic bromine atom is replaced by an -OH group to form phenylmethanol (benzyl alcohol) and NaBr .

🧠 Exam Technique

Go through the compounds one by one systematically:

  • Check for acidic protons ( -COOH and phenolic -OH ) which neutralize NaOH .
  • Check for halogen atoms attached to aliphatic carbon chains ( -CH₂Br ), which readily undergo nucleophilic substitution with warm NaOH(aq) .
  • Since all three matched a reactivity criterion, option A is the only logical choice.

❌ Common Errors

  • Forgetting phenol acidity: Students sometimes mistakenly think phenols are not acidic enough to react with NaOH(aq) because phenol is a weaker acid than carboxylic acids. However, it is sufficiently acidic to react with strong bases like sodium hydroxide.
  • Confusing halogenoarenes with halogenoalkanes: A halogen directly bonded to a benzene ring (aryl halide) is unreactive towards NaOH(aq) due to delocalization of the ring's electrons with the halogen lone pair. However, compound 3 features the bromine on a side-chain carbon ( -CH₂Br ), making it behave like a reactive primary halogenoalkane.
Mark Scheme Allocation: 1 mark total for selecting option A (AO1.2).

Topics

Module 6: Organic chemistry and analysis · Module 4: Core organic chemistry · 6.1 Aromatic compounds, carbonyls and acids · 4.2 Alcohols, haloalkanes and analysis

Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.