A student puts a drop of reaction mixture of a saponification reaction first on a blue litmus paper and then on a 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 colour is observed in both the litmus papers.

Question

A student puts a drop of reaction mixture of a saponification reaction first on a blue litmus paper and then on a 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 colour is observed in both the litmus papers.

Vedantu Content Team · Accepted Answer

Hint:    We all know that a saponification reaction involves the hydrolysis of an ester under acidic conditions or basic conditions and results in the formation of an alcohol and a salt of carboxylic acid. It basically refers to the reaction between metallic alkali and a fat or oil to produce soap.Complete step by step solution: So let us start with saponification which basically refers to the reaction between metallic alkali and a fat or oil to produce soap. It involves the hydrolysis of an ester under acidic or basic conditions and results in the formation of an alcohol and a salt of carboxylic acid. We also know that the litmus paper is a kind of filter paper which is treated with water soluble dye and it can be used as a pH indicator. So, under basic conditions, the red litmus paper turns blue and under acidic conditions, blue litmus paper turns red. Base does not affect blue litmus because it doesn’t consist of acidic ions which can turn blue litmus red. As the Saponification mixture is also a base, it will stay the same when it is poured on blue litmus as it requires (usually sodium hydroxide, $$NaOH$$) hydrolysis of triglycerides, which are fatty acid esters, to form carboxylate sodium salt. Therefore, the reaction mixture is basic. So, the student will observe that when the solution is poured on the red litmus, it will turn red litmus blue.Therefore the correct answer is (C).Note:  When conditions are basic, the red litmus paper turns blue and when the conditions are acidic, blue litmus paper turns red and the colour change usually occurs between the pH range of $4.5 - 8.3$. Also under neutral conditions the litmus paper is purple.