A Level Chemistry: Phenol — Reactions and Acidity Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs — examination boards hold copyright in their own papers. Use these alongside the official past papers available free from your board.

Related: Phenol: Reactions and Acidity study guide

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Section A

1. State the reagent needed to convert an alcohol to an ester faster and more completely than the equivalent reaction with a carboxylic acid. [1]

2. State the reagents/conditions for the nitration of phenol, and compare them with those needed for benzene. [2]

3. State the order of acidity (most to least acidic) of phenol, water and ethanol. [1]

4. State why phenol does not release CO₂ from aqueous sodium hydrogencarbonate. [1]

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Section B

5. Describe, with an equation, how phenol is produced from phenylamine, including approximate conditions for each step. [4]

6. Phenol reacts with bromine water at room temperature without a catalyst to give a white precipitate, whereas benzene does not react with bromine water at all under these conditions.

(a) Name the product of phenol’s reaction with excess bromine water and state its structural feature relevant to yield. [2]

(b) Explain, in terms of electron density, why phenol reacts so much more readily than benzene with Br₂(aq). [3]

7. Explain fully why phenol is a stronger acid than ethanol, referring to the structure and stability of the ions formed when each loses H⁺. [4]

8. Explain why phenol is a stronger acid than both water and ethanol, and why it reacts with NaOH(aq) to form a salt, while ethanol does not react with NaOH(aq) at all. [3]

9. CH₃CH₂OH is reacted with CH₃COCl.

(a) Write the equation for this reaction, naming the organic product. [2]

(b) State one advantage of this method over reacting the alcohol directly with the corresponding carboxylic acid. [1]

10. Phenol reacts with sodium metal, releasing a gas, and separately with a diazonium salt in alkaline solution.

(a) Write the equation for phenol’s reaction with sodium, and identify the gas released. [2]

(b) State the type of compound formed when phenol couples with benzenediazonium chloride under alkaline conditions, and name the functional group this reaction introduces. [2]

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Answers

1. An acyl chloride (e.g. CH₃COCl) [1].

2. Dilute HNO₃(aq), room temperature [1] — far milder than benzene’s requirement for concentrated HNO₃/concentrated H₂SO₄ at 25–60 °C [1].

3. Phenol > water > ethanol [1].

4. Phenol is a weaker acid than carbonic acid, so it is not a strong enough acid to displace CO₂ from HCO₃⁻ [1].

5. Phenylamine reacts with HNO₂ (generated in situ from NaNO₂ and dilute HCl), below 10 °C [1], to form the diazonium salt, benzenediazonium chloride:

C₆H₅NH₂ + HNO₂ + HCl → C₆H₅N₂⁺Cl⁻ + 2H₂O

[1] for the balanced equation. This diazonium salt is then warmed with water [1], which decomposes it to give phenol:

C₆H₅N₂⁺Cl⁻ + H₂O → C₆H₅OH + N₂ + HCl

[1] for the balanced equation.

6. (a) 2,4,6-tribromophenol [1] — all three ring positions activated by the –OH group’s directing effect react at once, giving the trisubstituted product directly [1].

(b) Phenol’s oxygen lone pair delocalises into the ring’s π system, substantially increasing the ring’s electron density [1] compared with benzene [1]. This makes the ring far more attractive to the electrophile, so only a dilute, uncatalysed source of Br⁺ (from Br₂(aq) alone) is needed to react, unlike benzene which needs an AlBr₃ catalyst to generate a sufficiently electrophilic species at all [1].

7. When phenol loses H⁺, the resulting phenoxide ion has its negative charge partially delocalised into the aromatic ring, spreading the charge over several ring carbons rather than leaving it concentrated on oxygen [1], which stabilises the ion [1]. When ethanol loses H⁺, the resulting ethoxide ion has no such delocalisation available, and the ethyl group’s electron-donating inductive effect further increases electron density on the already-negative oxygen, destabilising it [1]. Because the phenoxide ion is more stable relative to phenol than the ethoxide ion is relative to ethanol, H⁺ loss is more energetically favourable for phenol, making it the stronger acid [1].

8. Phenol is a stronger acid than both water and ethanol because the phenoxide ion formed on loss of H⁺ has its negative charge delocalised from oxygen into the aromatic ring, spreading the charge over several ring carbons and stabilising the ion [1]. Water and ethanol form OH⁻ and ethoxide ions respectively, neither of which has a ring to delocalise into, so their conjugate bases are less stabilised and both are weaker acids than phenol [1]. NaOH(aq) is a strong enough base to deprotonate phenol (pKa around 10), forming sodium phenoxide and water, but ethanol’s O–H is far less acidic (with no delocalisation and an electron-donating alkyl group destabilising the anion) and is not deprotonated by NaOH(aq) — it reacts only with sodium metal itself, not with a hydroxide base [1].

9. (a) CH₃CH₂OH + CH₃COCl → CH₃COOCH₂CH₃ + HCl [1]; product named ethyl ethanoate [1].

(b) The reaction with an acyl chloride is faster and goes essentially to completion, unlike the reversible, slower reaction between an alcohol and a carboxylic acid [1].

10. (a) 2C₆H₅OH + 2Na → 2C₆H₅ONa + H₂ [1]; the gas released is hydrogen [1]. (b) Phenol couples with the diazonium salt to form an azo compound [1], introducing the azo (–N=N–) group that links the two aromatic rings [1].

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Where marks are usually lost

• Using benzene-like conditions (concentrated acid mixture, or an AlBr₃/AlCl₃ catalyst) when describing phenol’s nitration or bromination — phenol needs only mild, dilute conditions.
• Explaining phenol’s acidity by comparing it only to benzene, rather than making the three-way comparison of water, phenol and ethanol that the syllabus sets: delocalisation stabilises the phenoxide ion but is absent in OH⁻ and ethoxide, and the ethyl group’s electron-donating effect makes ethoxide the least stable of the three conjugate bases.
• Forgetting that phenol reacts with NaOH but not with the weaker base NaHCO₃ — a common distinguishing test between a phenol and a carboxylic acid group.
• Naming the ester product incorrectly, or forgetting HCl is also produced in the acyl chloride reaction.
• Confusing the azo-coupling product with a simple substitution product, or omitting that the reaction needs alkaline conditions.