Question

Give a simple chemical test to distinguish between benzoic acid and ethyl benzoate.

Hint:

The sodium bicarbonate test is the most common diagnostic test for the carboxyl (\(-COOH\)) functional group.

Answer 1

One simple chemical test to distinguish between benzoic acid and ethyl benzoate is the sodium bicarbonate test (NaHCO₃).
- Benzoic acid reacts with sodium bicarbonate (\( NaHCO_3 \)) to release carbon dioxide gas because benzoic acid is a weak acid that can donate a proton:
\[ \text{C}_6\text{H}_5\text{COOH} + \text{NaHCO}_3 \rightarrow \text{C}_6\text{H}_5\text{COONa} + \text{CO}_2(g) + \text{H}_2\text{O} \] This reaction produces effervescence due to the release of carbon dioxide, which is a characteristic reaction of carboxylic acids.
- Ethyl benzoate, on the other hand, does not react with sodium bicarbonate because it is an ester and lacks the free carboxyl group (-COOH) required for the acid-base reaction. Therefore, no effervescence will be observed when ethyl benzoate is treated with sodium bicarbonate.
Hence, the presence of effervescence when treated with sodium bicarbonate confirms the presence of benzoic acid and distinguishes it from ethyl benzoate.