The depression in freezing point of water observed for the same amount of acetic acid, trichloroacetic acid and trifluoroacetic acid increases in the order given above. Explain, briefly.

Explanation

The depression in freezing points are in the order : acetic acid < trichloroacetic acid < trifluoroacetic acid

Fluorine, being most electronegative, has the highest electron withdrawing inductive effect. Consequently, trifluoroacetic acid is the strongest acid while acetic acid is the weakest acid. Methyl group in acetic acid is electron donating. Hence, trifluoroacetic acid ionises to the largest extent while acetic acid ionizes to the minimum extent to give ions in their solutions in water. Greater the number of ions produced, greater is the depression in freezing point. Hence, the depression in freezing point is maximum for the fluoroacetic acid and minimum for acetic acid.