In solution chemistry, what does molality measure?

• A. Moles of solute per liter of solution
• B. Volume of solute per volume of solution
• C. Moles of solute per kilogram of solvent
• D. Grams of solute per $100$ mL of solution

Answer: (C)

Verified step by step guidance

1. Understand that molality is a concentration unit used in solution chemistry to express the amount of solute relative to the amount of solvent, not the total solution volume.
2. Recall the definition of molality: it is the number of moles of solute divided by the mass of the solvent in kilograms.
3. Express molality mathematically as \(molality = \frac{\text{moles of solute}}{\text{kilograms of solvent}}\).
4. Note that molality differs from molarity, which is moles of solute per liter of solution, and from other concentration units based on volume or mass of solution.
5. Recognize that molality is especially useful when temperature changes occur because it depends on mass, which does not change with temperature, unlike volume.