Question

Explain why some of the non-ideal solutions show positive deviations, while some others show negative deviations from ideal behaviour.

Answer 1

Non-ideal solutions do not obey Raoult’s law over the entire concentration range because the intermolecular forces between solute and solvent are either weaker or stronger than those in the pure components. If the solute–solvent interactions are weaker, the solution shows a positive deviation with increased vapour pressure. If the interactions are stronger, the solution shows a negative deviation with decreased vapour pressure.