Question 22 of 39intermediate💡 UnderstandShort Answer3 marks

Give two reactions that show the acidic nature of phenol. Compare acidity of phenol with that of ethanol.

Correct Answer

Two reactions showing the acidic nature of phenol are:

  1. Reaction with metals: Phenol reacts with metals like sodium to form sodium phenoxide.
  2. Reaction with sodium hydroxide: Phenol reacts with aqueous sodium hydroxide to generate phenoxide ion.

Phenol is more acidic than ethanol. The pKa_a value of phenol is 10.0 while ethanol has a pKa_a of 15.9, making phenol a million times more acidic. This is because the phenoxide ion formed after ionisation is stabilised by resonance and charge delocalisation, which favours ionisation.

Exercise: EXERCISES | Q: 7.14 | (Page Page 31)
For More Understanding

Explanation

The answer is derived directly from the provided context. The text explicitly mentions that reactions with metals (sodium) and sodium hydroxide indicate phenol's acidic nature. For the comparison, Table 7.3 provides the pKa values (10.0 for phenol vs 15.9 for ethanol), and the text states phenol is 'million times more acidic than ethanol'. The reason for this acidity is attributed to the stability of the phenoxide ion due to resonance and charge delocalisation mentioned in the text.

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