Question

Which of the following pairs will exhibit negative deviation ?
A) CCl4 + C6H6
B) H2O + CH3OH
C) H2O + C2H5OH
D) phenol + aniline

Ans : D

please give detailed explanation. Got test tomorrow.

Answer 1

First i will explain what is positive and negative deviation from the roults law

positive deviation from Raoult’s law, A-B interactions are weaker than those between A-A or B-B, i.e., in this case the intermolecular attractive forces between the solute-solvent molecules are weaker than those between the solute-solute and solvent-solvent molecules
EX Mixtures of ethanol and acetonebehave in this manner. In pure ethanol, molecules are hydrogen bonded. On adding acetone, its molecules get in between the host molecules and break some of the hydrogen bonds between them. Due to weakening of interactions, the solution shows positive deviation from Raoult’s law

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.
Negative deviation of 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.