In solution chemistry, molality is defined as the amount of solute per mass of solvent. What are the correct units of molality?

• A. $\frac{mol}{kg}$ (moles of solute per kilogram of solvent)
• B. $\frac{mol}{L}$ (moles of solute per liter of solution)
• C. $\frac{g}{L}$ (grams of solute per liter of solution)
• D. $\frac{mol}{g}$ (moles of solute per gram of solution)

Answer: (A)

Verified step by step guidance

1. Recall the definition of molality: it is the amount of solute (in moles) divided by the mass of the solvent (in kilograms).
2. Express molality mathematically as \(\text{molality} = \frac{\text{moles of solute}}{\text{mass of solvent in kg}}\).
3. Identify the units for moles of solute as 'mol' and the units for mass of solvent as 'kg'.
4. Combine these units to write the units of molality as \(\frac{\text{mol}}{\text{kg}}\).
5. Understand that molality differs from molarity, which uses volume of solution (liters) in the denominator, so molality's correct units are moles per kilogram of solvent.