Question

How do association of solute molecules affect a colligative property?

Answer 1

1. Association of solute molecules reduces the number of solute particles in a solution because individual molecules combine to form larger aggregates or dimers.
2. Since colligative properties (such as boiling point elevation, freezing point depression, osmotic pressure, and vapour pressure lowering) depend only on the number of solute particles and not on their size or nature, this decrease in particle number leads to weaker colligative effects than expected.
3. As a result, the observed colligative property is lower, and the calculated molecular mass appears higher than the actual value.
4. The van’t Hoff factor (i) in such cases is less than 1, indicating a reduction in the number of effective solute particles due to association.