Question

Upon addition of phenolphthalein to the aqueous solution of borax, pink colour generates i.e. solution becomes pink. At this stage, if glycerol is being added to the pink coloured solution, it turns colourless. Highlight the phenomenon.

• A. Final solution becomes neutral
• B. Glycerol binds phenolphthalein
• C. Final solution becomes acidic
• D. Final solution becomes strongly alkaline

Hint:

Phenolphthalein is a strong pH indicator that turns pink in strongly alkaline solutions. The addition of glycerol does not neutralize but causes the indicator to lose its colour.

Answer 1

The Correct Option is D

Step 1: Understanding the colour change.
Phenolphthalein is a pH indicator that is colourless in acidic and neutral solutions and turns pink in basic (alkaline) solutions.
Step 2: Borax solution behaviour.
Borax, which is a basic compound, when dissolved in water, gives an alkaline solution. The presence of phenolphthalein in this solution turns it pink due to the basicity of borax.
Step 3: Adding glycerol.
When glycerol is added to the solution, it does not neutralize the alkalinity but rather interacts with phenolphthalein. This results in the colour disappearing, indicating that the solution has remained strongly alkaline and that the glycerol’s action is not to neutralize it.
Conclusion:
The solution remains strongly alkaline, which is why the phenolphthalein remains pink initially and turns colourless only when glycerol is added.