How would you distinguish experimentally between an alcohol and a carboxylic acid?

We can distinguish between an alcohol and a carboxylic acid on the basis of their reaction with carbonates and hydrogen carbonates. Acid reacts with carbonate and hydrogen carbonate to evolve CO2 gas that turns lime water milky.

Alcohols, on the other hand, do not react with carbonates and hydrogen carbonates.

(a) Acid test: Reaction with carbonates/hydrogen carbonates. Take samples of alcohol and carboxylic acid in 2 test tubes, and add sodium carbonate or sodium bicarbonate solution to each. The compound which will produce brisk effervescence of CO₂ gas will be acid. 

(b) Alcohol test: Take small amount of ethanol and ethanoic acid in test tube A and B. Add 5% solution of alkaline potassium permanganate drop by drop to this solution and warm the test tube. 

The colour of potassium permanganate will disappear in test tube containing alcohol.

We can distinguish  between an alcohol and a carboxylic acid:

1. Litmus test

• Take 2 ml of alcohol and carboxylic acid in a test tube, Put 1 drop of blue litmus in each test tube, the liquid which shows no effect is alcohol whereas the liquid which turns red is a carboxylic acid.

2. Sodium Bicarbonate test 

• Take a small amount of each compound in a test tube and add to it the aqueous solution of NaHCO₃.
• The compound which produces brisk effervescence due to the evolution of CO₂​must be a carboxylic acid whereas which shows no effect is alcohol.

Alcohols can be distinguished from carboxylic acid using the sodium carbonate (Na₂CO₃) or sodium bicarbonate (NaHCO₃) test. Alcohols do not react with sodium carbonate or bicarbonate, whereas acid reacts with them to release carbon dioxide.

2RCOOH + Na₂CO₃→ 2RCOONa + CO₂↑ + H₂O

RCOOH + NaHCO₃→ RCOONa + CO₂↑ + H₂O

Alcohol + Na₂CO₃→ No reaction

Sodium bicarbonate test is the best method to experimentally distinguish carboxylic acid from alcohol because even phenol does not respond to this test. In this test, carboxylic acid reacts with sodium bicarbonate to form sodium acetate and a brisk effervescence of CO₂. 

This effervescence is what indicates the carboxylic acid. 

RCOOH + NaHCO₃ → RCOONa + H₂O + CO₂ 

NOTE: Sodium bicarbonate test is also known as sodium hydrogen-carbonate test.