Question

List two tests for experimentally distinguishing between an alcohol and a carboxylic acid and describe how these tests are performed.

Answer 1

Alcohol is an organic compound that contains one or more than one hydroxyl (-OH) functional group attached to saturated carbon atom. Carboxylic acid is an organic compound that has a functional group (-COOH) attached to an alkyl group.

Complete Step by Step Solution:
There are many tests available through which we can distinguish between an alcohol and carboxylic acid experimentally but we discuss only two popular tests:

1. Ceric Ammonium Nitrate test: It is a group reagent test for alcohols. Alcohols ($1^\circ ,2^\circ ,3^\circ$) also give characteristics red color with ceric ammonium nitrate.

- Procedure for test-Take 1 mL solution of organic compound dissolved in a suitable solvent. Add a few drops of ceric ammonium nitrate solution. Appearance of red color shows the presence of alcohol – OH group.

2. Sodium bicarbonate test (NaHCO3): All carboxylic acids which are stronger than H2CO3 give CO2 gas with.

$$RCOOH + NaHC{O_3}\;R - COONa{\text{ }} + {\text{ }}{H_2}C{O_3}\;\; \\\ {H_2}O{\text{ }} + C{O_2} \\\$$

- Procedure for test- Take a few drops or a few crystals of the unknown sample and dissolved them in 1mL of methanol and slowly added to 1 mL of a saturated solution of sodium bicarbonate.
Evolution of $C{O_2}$ gas which turns lime water milky confirms the presence of carboxylic acid.

Additional Information:
If an electron withdrawing group is present at ortho or para position of phenol then it gives a positive test with sodium bicarbonate test.
In ceric ammonium nitrate test for alcohols, red color disappears after keeping the reaction mixture for some time. The color also disappears if excess of ceric ammonium nitrate solution is added. Therefore, use of excess of ceric ammonium nitrate solution should be avoided.

Note:
Remember in $NaHC{O_3}$test for carboxylic acid, acid must be stronger than ${H_2}C{O_3}.$