Question

Is molality or molarity dependent on temperature? Explain your answer. Why is molality, and not molarity, used in the equations describing freezing-point depression and boiling-point elevation?

Short answer

The molarity is dependent on temperature.

Step-by-step solution

Step 1:Concept

Molarity (M)of a solution is equal to the moles of solute per volume of the solution.

$\text{M}=\frac{\text{moles of solute}}{\text{liters of solution}}$.

Molality (m)of a solution is equal to the moles of solute per kilogram of solvent.

$\text{m}=\frac{\text{moles of solute}}{\text{kilogram of solvent}}$

The molarity is dependent on temperature because it depends on the volume of the solution.

Step 2:Explain the reasoning

If there is a dilute aqueous solution the molarity and molality are approximately equal. The approximation fails as a solution becomes more concentrated, and involves a solvent other than water.