State with a suitable diagram and appropriate examples why some non-ideal solutions. Show positive deviation from ideal behavour.

Answer:

In case of negative deviations from Raoult’s law, the intermolecular attractive forces between A-A and B-B are weaker than those between A-B and leads to decrease in vapour pressure resulting in negative
deviations. An example of this type is a mixture of phenol and aniline.

In this case the intermolecular hydrogen bonding between phenolic proton and lone pair on nitrogen atom of aniline is stronger than the respective intermolecular hydrogen bonding between similar
molecules.

This decreases the escaping tendency of molecules for each component and consequently the vapour pressure decreases resulting
in negative deviation from Raoult’s law