Why is molality often preferred over molarity for calculations involving temperature changes?

• A. Because molality depends on the volume of the solution, making it more accurate at different temperatures.
• B. Because molality is only used for gaseous solutions.
• C. Because molality does not change with temperature, while molarity can vary due to volume expansion or contraction.
• D. Because molality is always larger than molarity for any solution.

Answer: (C)

Verified step by step guidance

1. Understand the definitions: Molarity (M) is defined as moles of solute per liter of solution, while molality (m) is defined as moles of solute per kilogram of solvent.
2. Recognize that molarity depends on the volume of the solution, which can change with temperature due to expansion or contraction of the liquid.
3. Note that molality depends on the mass of the solvent, which does not change with temperature because mass is independent of temperature.
4. Therefore, when temperature changes, molarity can vary because the volume changes, but molality remains constant because the mass of solvent remains the same.
5. This makes molality more reliable and preferred for calculations involving temperature changes, such as colligative properties.