Why does phenolphthalein turn pink in sodium carbonate solution?
Answer and explanation
Correct answer: Because the solution is basic
The governing concept is the colour change of an acid-base indicator. Sodium carbonate is a salt of a strong base and a weak acid, so its aqueous solution is alkaline because carbonate ions react partly with water to produce hydroxide ions. Phenolphthalein is pink in a basic medium. Therefore option A correctly explains the observation. It is not caused by strong acidity, universal pink colour, or insolubility; sodium carbonate dissolves in water.
Frequently asked questions
What is the correct answer to this question?
Because the solution is basic
Why is this the correct answer?
The governing concept is the colour change of an acid-base indicator. Sodium carbonate is a salt of a strong base and a weak acid, so its aqueous solution is alkaline because carbonate ions react partly with water to produce hydroxide ions. Phenolphthalein is pink in a basic medium. Therefore option A correctly explains the observation. It is not caused by strong acidity, universal pink colour, or insolubility; sodium carbonate dissolves in water.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
