In which situation will phenolphthalein turn from colourless to pink?
Answer and explanation
Correct answer: When base is added to an acidic solution until it becomes basic
Phenolphthalein is colourless in acidic and generally neutral conditions, but it becomes pink in a basic medium. Therefore, when base is added to an acidic solution in sufficient amount to make the final solution basic, the indicator changes from colourless to pink. Adding acid to a base would remove the pink colour as the medium becomes acidic. The salt choices do not necessarily create a basic solution, so option A is correct.
Frequently asked questions
What is the correct answer to this question?
When base is added to an acidic solution until it becomes basic
Why is this the correct answer?
Phenolphthalein is colourless in acidic and generally neutral conditions, but it becomes pink in a basic medium. Therefore, when base is added to an acidic solution in sufficient amount to make the final solution basic, the indicator changes from colourless to pink. Adding acid to a base would remove the pink colour as the medium becomes acidic. The salt choices do not necessarily create a basic solution, so option A is correct.
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.
