Question

When phenolphthalein indicator is added to a colorless solution with a pH of 10, a student observes and concludes that the tested solution
1
remains colorless and is basic
2.
remains colorless and is acidic
3.
turns pink and is basic
4.
turns pink and is acidic

Answer 1

Answer:

3.  turns pink and is basic

Explanation:

Phenolphthalein is a pH indicator that remains colorless in acidic solutions, but in basic solutions it turns pink at a pH equal to 10.

Phenolphthalein is a weak acid that loses H+ cations in solution. The phenolphthalein molecule is colorless, while the phenolphthalein-derived anion is pink. When a base is added, phenolphthalein loses H+, forming the anion and causing it to turn pink. The color change cannot be explained only on the basis of deprotonation, a structural change occurs with the appearance of a ketoenolic tautomerism.