Question

When two liquids A and B are mixed, their boiling points become greater than both of them. The mixture is:

A. Ideal solution

B. Non-ideal solution with negative deviation from Raoult’s law

C. Non-ideal solution with positive deviation from Raoult’s law

D. Normal solution

Answer 1

Boiling point of a substance is the temperature at which the vapour pressure of a liquid equals the pressure surrounding the liquid and liquid changes into a vapour. Ideal solution is a solution in which force exerted on the molecules is the same for all molecules independent of species.

Complete step by step answer:

To answer this question, we need to know few topics.

Boiling point: Boiling point of a substance is the temperature at which the vapour pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapour. The boiling point of a liquid varies depending upon the surrounding environmental pressure. This means a liquid in a partial vacuum has a lower boiling point than when that liquid is at atmospheric pressure.

Ideal solution is a mixture in which the molecules of different species are distinguishable and these molecules in the ideal solution exert forces on one another. When those forces are the same for all molecules independent of species, then a solution is said to be ideal. Non-ideal solution is a solution that does not abide by the rules of an ideal solution.

Raoult’s law states that “the relative lowering of the vapour pressure of a solvent by dissolving a non-volatile electrolyte is equal to the mole fraction of the solute.” In other words, the partial pressure of each component of an ideal mixture of liquids is equal to the vapour pressure of the pure component multiplied by its mole fraction in the mixture. Deviations from Raoult’s law can either be positive or negative. A positive deviation means that there is higher than expected vapour pressure above the solution. Negative deviation means that we find a lower than expected vapour pressure for the solution.

Now since the vapour pressure is inversely proportional to the boiling point so when boiling point increases , it means that vapour pressure decreases and hence it will show negative deviation with Non-ideal solution.

Therefore, the correct answer is option C.

Note:
Raoult’s law states that the partial pressure of each component of an ideal mixture of liquid is equal to the vapour pressure of the pure component multiplied by its mole fraction in the mixture.