Phenolphthalein is pink in a basic solution. What does becoming colourless on adding acid indicate?
Answer and explanation
Correct answer: Basicity decreased and a neutral or acidic condition was reached
Phenolphthalein is colourless in acidic or neutral conditions and pink in a sufficiently basic medium. Adding acid consumes hydroxide ions and lowers the pH, so the basic character gradually decreases. When the indicator becomes colourless, the solution has reached the indicator’s colour-change range; it may be neutral or may have become acidic if more acid is added. Thus A is the precise choice.
Frequently asked questions
What is the correct answer to this question?
Basicity decreased and a neutral or acidic condition was reached
Why is this the correct answer?
Phenolphthalein is colourless in acidic or neutral conditions and pink in a sufficiently basic medium. Adding acid consumes hydroxide ions and lowers the pH, so the basic character gradually decreases. When the indicator becomes colourless, the solution has reached the indicator’s colour-change range; it may be neutral or may have become acidic if more acid is added. Thus A is the precise choice.
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.
