Question

Calculate the molality of a solution prepared by dissolving 5 g of NaOH in 450 g of water. (Molar mass of NaOH = 40 g/mol)

Hint:

Always convert the solvent's mass to kg when calculating molality. Molality is temperature independent and used in colligative properties.

Answer 1

Step 1: Use the formula for molality: \[ \text{Molality (m)} = \frac{\text{moles of solute}}{\text{mass of solvent in kg}} \] Step 2: Calculate moles of NaOH \[ \text{Moles} = \frac{5}{40} = 0.125 \text{ mol} \] Step 3: Convert mass of solvent to kg \[ 450\,g = 0.450\,kg \] \[ \text{Molality} = \frac{0.125}{0.450} \approx 0.278 \, mol/kg \] Final Answer: \[ \boxed{0.278\,mol/kg} \]