Which expression correctly defines the molality of a solution?

• A. $m=\frac{n(\text{solute})}{m(\text{solvent})(kg)}$
• B. $m=\frac{m(\text{solute})(g)}{m(\text{solution})(kg)}$
• C. $m=\frac{n(\text{solute})}{V(\text{solution})(L)}$
• D. $M=\frac{n(\text{solute})}{V(\text{solution})(L)}$

Answer: (A)

Verified step by step guidance

1. Understand that molality (denoted as \(m\)) is defined as the amount of solute (in moles) per kilogram of solvent, not solution.
2. Identify the variables: \(n(\text{solute})\) represents the number of moles of solute, and \(m(\text{solvent})\) represents the mass of the solvent in kilograms.
3. Write the formula for molality as \(m = \frac{n(\text{solute})}{m(\text{solvent})}\), where the numerator is moles of solute and the denominator is kilograms of solvent.
4. Note that molality differs from molarity, which uses volume of solution in liters in the denominator, and from mass percent, which uses mass of solution.
5. Confirm that the correct expression for molality does not involve volume or mass of the entire solution, but specifically moles of solute divided by kilograms of solvent.