Question

Why does chloroform and benzene show negative deviation?

Answer 1

Chloroform and benzen (CHCl3 andC6H,6): Benzen does not associate through hydrogen bonding. So, when chloroform is added to benzene, there is Hydrogen bonding between Hydrogen of chloroform and Oxygen of benzen . The presence of three chlorine atoms will not hinder the Hydrogen bonding due to the presence of electron releasing Carbon. Hence, the molecular interaction in the solution increases and there is a negative deviation.

Answer 2

Explanation: When chloroform and benzene are mixed there are strong interactions between the delocalised electrons of benzene and the positive charge on carbon atom of chloroform (Cl being more electronegative than C).

The resulting interaction is stronger than those between CHCl3-CHCl3 and benzene-benzene molecules separately. Now, the escaping tendency of molecules decreases, thereby reducing the vapour pressure. This leads to negative deviation.

Hope it helps!