Question

State the colour of phenolphthalein in soap solution.

Answer 1

Hint : Phenolphthalein is an organic compound. Its chemical formula is ${C_{20}}{H_{14}}{O_4}$. It is used as an indicator in acid-base titration. Phenolphthalein is a synthetic indicator.

Complete Step By Step Answer:
As we know that in acidic solutions, phenolphthalein is colourless while in basic solutions it turns pink.
Phenolphthalein is a weak acid which can be used in acid base titrations. It belongs to the class of dyes called Phthalein dyes. It does not have taste or smell. The end point is indicated by the formation of a pink colour since this compound dissociates to form pink anions when dissolved in water.
Soap is basic in nature; hence soap solution is also basic in nature. Soap is formed by a process of saponification where ethyl ethanoate is reacted in presence of a base. Therefore, it is basic in nature.
As we know, phenolphthalein shows pink colour in basic solutions, it will show pink colour in soap solution.
Phenolphthalein is used in the Kastle-Meyer test. Before it was also used as a laxative.
The chemical compound is widely used as pH indicator and laboratory agent.

Additional Information:
Indicators are divided into three categories:
Natural indicators: Indicators prepared from natural substances are called natural indicators. Example: Red Cabbage
Olfactory indicators: Indicators which give different odours in acidic and basic solutions are called olfactory indicators. Example: Onion.

Note :
Synthetic indicators are indicators which are synthesized in the laboratory. Some other examples of synthetic indicators are methyl orange, litmus paper. Soaps are water soluble sodium or potassium salts of fatty acids.