Question

A student put a drop of the reaction mixture of a saponification reaction first on blue litmus paper and then on red litmus paper. He may observe that:

• A. There is no change in the blue litmus paper and the red litmus paper turns white.
• B. There is no change in the red litmus paper and the blue litmus paper turns red.
• C. There is no change in the blue litmus paper and the red litmus paper turns blue.
• D. No change in color is observed in both the litmus paper.

Answer 1

The correct option is C

There is no change in the blue litmus paper and the red litmus paper turns blue.

The explanation for the correct option:

C: There is no change in the blue litmus paper and the red litmus paper turns blue.

• Hydrolysis of an ester under acidic and basic conditions may involve the formation of an alcohol and carboxylic acid.
• The process is so-called the saponification reaction.
• The reaction occurs between metallic alkali and fat to produce soap.
• Litmus paper can be used as a pH indicator and is a kind of filter paper.
• This is to be noted that under the basic condition the red litmus paper turns blue and similarly to the case under acidic conditions blue litmus paper turns red.
• Base does not change the blue litmus as they do not contain any acidic ions.
• Saponification mixture is also basic in nature when poured on blue litmus, no significant change can be observed in color.
• The required condition is the hydrolysis of fatty acid esters to form carboxylate sodium salts.
• Take an example of Ethyl ethanoate(ester) reacting with Sodium hydroxide to form Sodium ethanoate and Alcohol.
• The chemical reaction occurs as follows:
• $\underset{\left(\mathrm{Ethyl}\mathrm{ethanoate}\right)}{{\mathrm{CH}}_3{\mathrm{COOC}}_2{\mathrm{H}}_5}\left(\mathrm{l}\right)+\underset{\left(\mathrm{Sodium}\mathrm{hydroxide}\right)}{\mathrm{NaOH}\left(\mathrm{s}\right)}\to \underset{\left(\mathrm{Sodium}\mathrm{ethanoate}\right)}{{\mathrm{CH}}_3\mathrm{COONa}\left(\mathrm{s}\right)}+\underset{\left(\mathrm{Ethanol}\right)}{{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}\left(\mathrm{l}\right)}$
• Therefore, we concluded that the reaction mixture is basic in nature.
• The student will observe that the red litmus turns blue when the solution is poured on it.

There is no change in the blue litmus paper and the red litmus paper turns blue. Hence the correct option is C.