Question

Equimolar solutions in the same solvent have:
A.Same boiling point but different freezing point
B.Same freezing point but different boiling point
C.Same boiling and same freezing points
D.Different boiling and freezing points.

Answer 1

To answer this question, you must recall the colligative properties of a solution. Those properties which depend only on the number of solute particles are known as colligative properties.

Complete step by step answer:
The vapour pressure of a solution (containing a non-volatile solute) is lower than that of a pure solvent. We know that the boiling point of a liquid is the temperature at which its vapour pressure becomes equal to the atmospheric pressure, that is 760 mm of Hg column. As a result, the boiling point of a solution will always be higher than that of the pure solvent. This increase in the boiling point of a liquid in addition of a solute or impurity is known as elevation in boiling point.
We know that, freezing point of a liquid is the temperature at which the solid state and the liquid state of the substance have the same vapour pressure. Since the vapour pressure of a solution is lower than that of a pure solvent, then it is clear that the freezing point of a solution will be lower than that of pure solvent. This decrease in the freezing point of a liquid on addition of a solute or impurity is known as depression in freezing point.
Both the elevation in boiling point and depression in freezing point are colligative properties.
We know that equimolar solutions of non-electrolyte solutes have the same number of particles in the solution, thus they will have the same boiling point and freezing point.

The correct option is C.

Note:
Other than the elevation in boiling point and depression in freezing point, there are two more colligative properties, namely, relative lowering of vapour pressure and osmotic pressure. The colligative properties are independent of the nature of the solute and depends only on the number of particles present in the solution.