Question

the equation used to calculate the change in freezing point ($delta t_{f}$) of a substance is $delta t_{f}=k_{f}m$ where $k_{f}$ is the freezing - point depression constant and $m$ is the molality of the solution. which of the statements explains why molality is used instead of molarity in this equation? as the temperature of a solution changes, its volume will also change, which will affect its molarity but not its molality. molality does not appear in many equations, so it is used here to distinguish this equation from other similar ones. the equation was originally published with $m$ as a typo, rather than $m$, but the values are close enough that the equation is still valid. in solutions, moles are not directly related to grams and the freezing point of a solution is dependent solely on the number of grams of solute.

Explanation:

Molarity is defined as moles of solute per liter of solution and is volume - dependent. Since volume changes with temperature, molarity also changes with temperature. Molality is defined as moles of solute per kilogram of solvent and is not affected by temperature - induced volume changes. So, molality is used in the freezing - point depression equation because temperature changes affect molarity but not molality.

Answer:

As the temperature of a solution changes, its volume will also change, which will affect its molarity but not its molality.