Question

Which of the following solutions is an example of negative deviation from Raoult’s law?
A. Acetone + Ethanol
B. Carbon tetrachloride + Chloroform
C. Acetone + Chloroform
D. Water + Ethanol

Answer 1

The solution shows negative deviation from Raoult’s law when the forces between the particles of the solution mixture are stronger than the forces between the particles in the pure liquid.

Complete answer:
The above question belongs to the concept of solutions and its properties. Some solutions show negative deviation and some show positive deviation with respect to Raoult’s law. A solution gives positive deviation from Raoult’s law if the vapour pressure is higher, then the solution and. A solution gives negative deviation from Raoult’s law if the vapour pressure is lower, then the solution. Whereas Raoult’s law states the vapour pressure of a component at a given temperature is equal to the mole fraction of the component in the solution multiplied by the vapour pressure of that component in its pure state. With the help of Raoult’s law we can estimate the contribution of individual components of a mixture in the total pressure of the system. The biggest drawback or limitation of Raoult’s law is it is only applicable for non-volatile solutes.
if the solute and the solvent have low intermolecular attractions , which means they are not tightly held together by each other then the solution will show positive deviation from the Raoult’s law as the solvent molecules will easily escape into the gas phase as the attractions are not that much strong but on the other hand when the solvent molecules and the solute molecules are tightly held by their binding forces then the solution shows negative deviation from Raoult’s law because the solvent molecules will not be able to escape easily into gas phase.
Now in the given question each pair will show positive deviation from Raoult’s law except the mixture of Acetone + Chloroform because their solute-solvent attractions are the highest among the given options.

Therefore, option (C) is the correct answer.

Note:
When acetone and chloroform are mixed together, it results in the formation of hydrogen bonds between them and this results in the decrease in vapour pressure.