Question

What will you observe when -

(iii) a drop of phenolphthalein is added to solution of lime water?

Answer 1

Phenolphthalein:

1. Phenolphthalein, (C₂₀H₁₄O₄), is an organic compound of the phthalein family that is widely employed as an acid-base indicator.
2. As an indicator of a solution's pH, phenolphthalein is colorless below pH 8.5 and attains a pink to deep red hue above pH 9.0.

Lime water:

1. Limewater is the common name for a saturated aqueous solution of calcium hydroxide.
2. Calcium hydroxide, Ca(OH)₂, is sparsely soluble at room temperature in water.
3. It is basic in nature with a pH of 12.4

A drop of phenolphthalein is added to a solution of lime water:

1. Phenolphthalein remains in its concentrated form in an acidic medium which is colorless.
2. Whereas in the basic medium OH ions ionize it and convert it into the ionized form which is pink in color.
3. Therefore, if a drop of phenolphthalein is added to lime water ( that is calcium hydroxide ) then the solution will turn colorless to pink color showing that the lime water is basic in nature.