Question

Give any two tests to identify carboxylic acids.

Answer 1

Hint: Carboxylic acids are organic compounds which contain carboxyl groups attached to the R-group. The general formula of carboxylic acid is \[R-COOH\], where R refers to alkyl groups.

Complete answer:
Carboxylic acids are organic compounds generally containing carboxyl groups attached to the R-group. The general formula of carboxylic acid is \[R-COOH\]. Suffix used for carboxylic acids -oic acid. For example \[C{{H}_{3}}COOH\] (methanoic acid), \[C{{H}_{3}}C{{H}_{2}}COOH\] (ethanoic acid). Carboxylic acids are polar in nature because they are both hydrogen-bond acceptors (the carbonyl \[-C=O\] and hydrogen-bond donors (the hydroxyl \[-OH\] and participate in hydrogen bonding. Carboxylic acids often have strong sour odors. Carboxylic acids tend to have higher boiling points than water, because of their greater surface areas and tendency to form stabilized dimers through hydrogen bonds.
There are many tests to identify carboxylic acid out of which two are:

a) Litmus Test:
Acids are the substances which turn blue litmus paper to red. The carboxylic acid also turns the blue litmus paper into red due to the presence of the hydroxyl group present in \[COOH\] which is very acidic in nature as compared to alcohol.
The chemical reaction is as shown:
\[RCOOH+{{H}_{2}}O\to RCO{{O}^{-}}+{{H}_{3}}{{O}^{+}}\]
If the color of the blue litmus paper changes to red then a carboxyl group is present but this phenol also gives this test so we have to identify another test which gives results only for carboxylic acids.

(b) Sodium Bicarbonate Test:
When carboxylic acid reacts with sodium bicarbonate solution carbon dioxide is evolved with a brisk effervescence and sodium acetate is formed in this reaction and water is also produced.
The chemical reaction is as shown:
\[RCOOH+NaHC{{O}_{3}}\to RCOONa+{{H}_{2}}O+C{{O}_{2}}\]
This test is used to distinguish between carboxylic acid from phenol as phenol does not give this test.

Note:
Carboxylic acids are mainly those organic compounds which have \[COOH\] group and mainly termed as oic acid like methanoic, butanoic acids. There are many tests to identify the presence of carboxylic groups out of which two main methods; litmus test and sodium bicarbonate tests are performed to identify the \[COOH\] group other than these ester tests are also there.