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A2 · Practice questions · Phenol

Activate the ring.

Six original Cambridge-style questions on phenol.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
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Weak acid, very reactive ring.

01
Recall
[3 marks]

Describe how phenol is made from phenylamine, giving reagents, conditions and equations.

  • React phenylamine with NaNO2 and HCl(aq) below 10 °C: C6H5NH2 + HNO2 + HCl → C6H5N2+Cl− + 2H2O. ✓
  • Warm the benzenediazonium chloride solution with water. ✓
  • C6H5N2+ + H2O → C6H5OH + N2 + H+. ✓
02
Explain
[3 marks]

Explain why phenol is more acidic than ethanol.

  • A lone pair on the O of the phenoxide ion overlaps with the delocalised π electrons of the ring. ✓
  • So the negative charge is spread over the ring and the phenoxide ion is stabilised. ✓
  • In ethoxide the charge stays on O and is intensified by the electron-donating ethyl group, so ethanol ionises far less. ✓
03
Calculation
[2 marks]

Calculate the pH of a 0.100 mol dm−3 solution of phenol (pKa 10.0).

  • Ka = 1.00 × 10−10 mol dm−3; [H+] = √(1.00 × 10−10 × 0.100) = 3.16 × 10−6 mol dm−3. ✓
  • pH = −log(3.16 × 10−6) = 5.50. ✓
04
Analysis
[3 marks]

Compare the bromination of phenol with that of benzene: reagents, conditions, product and reason for the difference.

  • Phenol: bromine water at room temperature, no catalyst; white precipitate of 2,4,6-tribromophenol (+ 3HBr). ✓
  • Benzene: liquid Br2 with a FeBr3 (or AlBr3) halogen carrier; bromobenzene only. ✓
  • The O lone pair in phenol increases the electron density of the ring (especially at 2, 4 and 6), so it can polarise Br2 itself. ✓
05
Calculation
[2 marks]

4.70 g of phenol reacts with excess ethanoyl chloride and 5.44 g of phenyl ethanoate (Mr 136.0) is collected. Calculate the percentage yield.

  • n(phenol) = 4.70 ÷ 94.0 = 0.0500 mol, so the maximum is 0.0500 × 136.0 = 6.80 g. ✓
  • Yield = 5.44 ÷ 6.80 × 100 = 80.0%. ✓
06
Recall
[2 marks]

Benzenediazonium chloride is added to an alkaline solution of phenol below 10 °C. Name the type of reaction, the type of product and give its structural formula.

  • A coupling reaction (electrophilic substitution at the 4-position of phenol), forming an azo dye. ✓
  • 4-hydroxyazobenzene, C6H5N=NC6H4OH, a yellow-orange solid. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.