question_answer

Which of the following liquid pairs shows a positive deviation from Raoult's law?

A) Water - Nitric acid

B) Benzene - Methanol

C) Water-Hydrochloric acid

D) Acetone - Chloroform

Correct Answer: B

Solution :

[b] Positive deviations are shown by such solutions in which solvent-solvent and solute-solute interactions are stronger than becomes weaker. Therefore their escaping tendency increases which results in the increase in their partial vapour pressures. In pure methanol there exists intermolecular H-bonding. On adding benzene, its molecules come between methanol molecules there by breaking H-bonds which weaken intermolecular forces. This results in increase in vapour pressure.