Phenol is a compound that shares some properties with alcohols but also has distinctive chemical properties of its own. Describe the reaction of phenol with sodium hydroxide solution and explain how this reaction shows that phenol is more acidic than a typical alcohol such as ethanol.

WJEC A-Level Chemistry (Wales) — 4.3 Alcohols and phenols · Describe · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Phenol (C₆H₅OH) is widely used as an antiseptic and as a starting material in the manufacture of plastics. Unlike ethanol, phenol reacts readily with sodium hydroxide solution.

Model answer (5 marks)

Phenol reacts with sodium hydroxide to give sodium phenoxide and water:
C₆H₅OH + NaOH → C₆H₅ONa + H₂O

In this reaction the hydroxide ion accepts a proton from phenol, showing that phenol behaves as an acid.

Ethanol does not react with NaOH under the same conditions, so it does not donate a proton to the hydroxide ion.

Both phenol and ethanol can react with sodium metal to give hydrogen gas, but only phenol reacts with NaOH. This demonstrates that phenol is more acidic than ethanol.

Phenol is a weak acid – it is less acidic than a strong mineral acid such as HCl and does not react with carbonates.

Examiner tips

  • Use the balanced equation for the NaOH reaction; include the formation of sodium phenoxide. Show that the reaction involves proton transfer to hydroxide. Contrast with ethanol’s lack of reaction with NaOH. Mention the sodium metal test to emphasise relative acidity.
  • common_mistakes
  • :
  • Writing the reaction as phenol + NaOH → phenol + NaOH (no change). Forgetting to state that ethanol does not react with NaOH. Claiming phenol is a strong acid or that it reacts with carbonates.

Mark scheme (5 marks)

  1. Phenol reacts with sodium hydroxide solution to form sodium phenoxide (sodium phenate) and water
  2. This reaction shows phenol is acidic / behaves as an acid because it donates a proton (H⁺) to the hydroxide ion / neutralises a base
  3. Ethanol does NOT react with sodium hydroxide solution
  4. Both ethanol and phenol react with sodium metal to produce hydrogen gas, but only phenol reacts with sodium hydroxide, showing phenol is the more acidic of the two
  5. Phenol is a weak acid / it is less acidic than a typical mineral acid such as hydrochloric acid and does not react with carbonates

Key terms in this question

phenol · acidic · sodium hydroxide · ethanol

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