Hydrochloric acid is not suitable in the preparation of ethanoic acid because it

Analyze the question The question asks why HCl is unsuitable for preparing ethanoic acid. In the lab, ethanoic acid is made by heating a salt such as sodium ethanoate with a stronger, non-volatile acid. The acid used must displace the weak acid from its salt without being carried over into the product.

Explain the concept Ethanoic acid is a weak acid, so a stronger acid can displace it from its salt:

CH₃COONa + H⁺ → CH₃COOH + Na⁺

The reaction mixture is then heated and the ethanoic acid is distilled off. This only works if the displacing acid stays behind in the flask. Concentrated H₂SO₄ is used because it is non-volatile (high boiling point).

Step-by-step solution

1. HCl (as hydrogen chloride gas or concentrated solution) is highly volatile.
2. When the mixture is heated to distil the ethanoic acid, HCl also vaporises and distils over with it.
3. The ethanoic acid distillate is then contaminated with HCl, so it is impure.

Checking the other options:

• A. Too acidic: Being a strong acid is actually the requirement for displacing ethanoic acid, so this is not a drawback.
• C. Attacks cork and rubber: This is not the main reason. The key issue is contamination of the product.
• D. Turns blue litmus red: All acids do this, including ethanoic acid, so it says nothing about suitability.

Answer: The correct option is B. is too volatile.

Exam tip: In preparing a volatile acid, you need a non-volatile acid. Remember "H₂SO₄ stays, HCl strays". Concentrated H₂SO₄ (or H₃PO₄) is used because it does not distil over with the product.