Question

A few drops of phenolphthalein are put in an unknown colourless solution. It is observed that the colour of the solution changes to pink. Its pH is likely to be:

[0.8 mark]

• A. 7
• B. 0
• C. Less than 7
• D. More than 7

Answer 1

The correct option is D More than 7

Phenolphthalein is used as an acid-base indicator as it shows different colours in acidic and basic solutions. Phenolphthalein shows no colour in an acidic solution while it turns pink in a basic solution.
According to the given information, the given solution turns pink with phenolphthalein. Thus, it must be basic in nature. The pH value of acids is less than 7 while that of bases is more than 7.
Hence, the pH of the given solution must be greater than 7.