Question

The value of molecular mass determined by colligative property measurement is sometimes abnormal.

1. Explain these abnormalities in the case of benzoic acid in benzene and KCl in water. 

2. What is van’t Hoff factor?

Answer 1

1. This is caused by dissociation in the case of KCl and association in the case of acetic acid. KCl in aqueous solution undergoes dissociation as KCl → K⁺ + Cl^-

Molecules of ethanoic acid (acetic acid) dimerises in benzene due to hydrogen bonding.

As a result of dimerisation the actual number of solute particles in solution is decreased. As colligative property decreases molecular mass increases.

2.