Which of the following best describes how molality differs from molarity?

• A. Molality is defined as moles of solute per kilogram of solvent, while molarity is moles of solute per liter of solution.
• B. Molality and molarity are both defined as moles of solute per liter of solvent.
• C. Molality is defined as moles of solute per liter of solution, while molarity is moles of solute per kilogram of solvent.
• D. Molality and molarity are both defined as moles of solute per kilogram of solution.

Answer: (A)

Verified step by step guidance

1. Understand the definitions of molality and molarity, which are both concentration units used in chemistry to express the amount of solute in a solution.
2. Molality (m) is defined as the number of moles of solute divided by the mass of the solvent in kilograms. Mathematically, it is expressed as: \[ m = \frac{\text{moles of solute}}{\text{kilograms of solvent}} \]
3. Molarity (M) is defined as the number of moles of solute divided by the volume of the entire solution in liters. It is given by: \[ M = \frac{\text{moles of solute}}{\text{liters of solution}} \]
4. Note the key difference: molality depends on the mass of the solvent only, while molarity depends on the total volume of the solution (solute + solvent).
5. Use this understanding to evaluate the given options and identify the correct description that matches these definitions.