Question

An aqueous solution ‘A’ turns the phenolphthalein solution pink. On addition of an aqueous solution ‘B’ to ‘A’, the pink colour disappears. Which of the following statement is true for the solutions ‘A’ and ‘B’.

Options

• A is strongly basic and B is a weak base.

• A is strongly acidic and B is a weak acid.

• A has a pH greater than 7 and B has a pH less than 7.

• A has a pH less than 7 and B has a pH greater than 7.

Answer 1

A has a pH greater than 7 and B has a pH less than 7.

Explanation:

Phenolphthalein is pink in basic solutions (turns pink when pH is above its transition range) and is colorless in acidic/neutral solutions. When B is added the pink disappears because B is acidic and lowers the pH below the indicator’s pink range, so N is basic and B is acidic.