On adding acid to a solution, the pink colour of phenolphthalein disappears. What was the initial nature of the solution?
Answer and explanation
Correct answer: Basic
Phenolphthalein is colourless in acidic or neutral conditions but turns pink in a sufficiently basic solution. If adding acid makes the pink colour disappear, the solution must initially have contained enough base to produce that colour. The acid lowers the alkalinity through neutralisation. Thus option B is correct; the other choices cannot explain the initial pink indicator colour.
Frequently asked questions
What is the correct answer to this question?
Basic
Why is this the correct answer?
Phenolphthalein is colourless in acidic or neutral conditions but turns pink in a sufficiently basic solution. If adding acid makes the pink colour disappear, the solution must initially have contained enough base to produce that colour. The acid lowers the alkalinity through neutralisation. Thus option B is correct; the other choices cannot explain the initial pink indicator colour.
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.
