If a base solution turns phenolphthalein pink, when will the pink colour disappear on adding acid?
Answer and explanation
Correct answer: When the basicity of the solution greatly decreases
The governing concept is the indicator colour change during neutralisation. Phenolphthalein is pink in a sufficiently basic medium but becomes colourless when the solution is no longer sufficiently basic. Adding acid consumes hydroxide ions and lowers the solution’s basicity. Therefore option A is correct. More basic conditions preserve or intensify the pink colour, while metal formation and guaranteed carbon dioxide are irrelevant.
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What is the correct answer to this question?
When the basicity of the solution greatly decreases
Why is this the correct answer?
The governing concept is the indicator colour change during neutralisation. Phenolphthalein is pink in a sufficiently basic medium but becomes colourless when the solution is no longer sufficiently basic. Adding acid consumes hydroxide ions and lowers the solution’s basicity. Therefore option A is correct. More basic conditions preserve or intensify the pink colour, while metal formation and guaranteed carbon dioxide are irrelevant.
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.
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