Science
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.
Acids Bases Salts
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Answer
A has a pH greater than 7 and B has a pH less than 7.
Reason — Phenolphthalein is colourless in acidic/neutral solutions and turns pink in basic solutions (typically pH ≳ 8.2). Since solution A turns phenolphthalein pink, A must be basic (pH > 7).
When solution B is added, the pink colour disappears, meaning B neutralizes the base and shifts the pH to acidic/neutral; therefore, B must be acidic (pH < 7).
So, A has a pH greater than 7 and B has a pH less than 7.
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