Question
Mixture of chloroform and acetone forms a solution with negative deviation from Raoult's law due to
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NEET UG Re-Exam 2026 Question Paper (21-Jun-2026)
The correct answer is
formation of hydrogen bonding between acetone and chloroform.
Understanding Negative Deviation in Chloroform-Acetone Mixtures
Negative deviation from Raoult's law occurs when the vapor pressure of a solution is consistently lower than predicted by Raoult's law for an ideal solution. This phenomenon indicates that the intermolecular attractive forces between the solute and solvent molecules in the mixture are stronger than the forces between molecules of the pure components.
Analyzing Interactions in Chloroform-Acetone Mixtures
To understand the negative deviation in a mixture of chloroform (CHCl3) and acetone (CH3COCH3), consider the intermolecular forces:
- In pure components, molecules interact via dipole-dipole forces and van der Waals forces.
- When chloroform and acetone are mixed, a new type of interaction occurs: hydrogen bonding. The hydrogen atom in chloroform, bonded to chlorine, becomes partially positive. This hydrogen can form a hydrogen bond with the partially negative oxygen atom of the carbonyl group (C=O) in acetone.
- This specific formation of hydrogen bonding between CHCl3 and CH3COCH3 molecules creates stronger attractions between the unlike molecules compared to the attractions between like molecules (CHCl3-CHCl3 or CH3COCH3-CH3COCH3).
- Because the intermolecular forces in the mixture are stronger, molecules have a reduced tendency to escape from the liquid phase into the vapor phase.
- This leads to a lower vapor pressure than theoretically predicted by Raoult's law, resulting in negative deviation.
The key factor driving this negative deviation is the stabilization of the mixture through the formation of hydrogen bonds between chloroform and acetone.
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