Question

Which of the following liquid will have total vapour pressure less than what it should be according to Raoult's Law?

• A. Liquid showing positive deviation from Raoult's law
• B. Liquid showing negative deviation from Raoult's law
• C. Liquids obeying Raoult's law.
• D. Mixture of benzene and toluene

Answer 1

The correct option is B Liquid showing negative deviation from Raoult's law

Liquids showing negative deviation will have total vapour pressure less than what it should be according to Raoult's Law because solvent-solute interaction is more than the solvent-solvent and the solute-solute interactions
$P_T<p_A^{\circ }{\chi }_A+p_B^{\circ }{\chi }_B$

For an ideal soluton : Follows Raoult Law

$P_T=p_A^{\circ }{\chi }_A+p_B^{\circ }{\chi }_B$

Mixture of benzene and toluene is an ideal solution. Here , solvent-solute interaction is equal to the solvent-solvent and the solute-solute interactions.

Acetone and $CHC{l}_3$ are the non-ideal solution and shows negative deviation from Raoult's law