Question

Why boiling point increases and Melting point decreases on adding impurities to a pure substance?

Answer 1

Dear Student,

When impurities are added to a pure substance, it takes the place of pure molecules or replace the pure particles by itself. And now it takes more heat to evaporate the impure particles rather than pure particles therefore the overall boiling point increases.

Melting point on the other hand decreases because when the impurities added in the pure substances, it gets its place in between the pure particles and hence disturbing the intermolecular forces of attraction and the whole lot structure (crystal lattice) of the pure substance. So, it becomes easier to distort the substance.

Regards.