Question

25g of NaOH is dissolved in 100g of water. Calculate the molality of the solution.

• A. 5.25 m
• B. 6.25 m
• C. 4.25 m
• D. 3.25 m

Answer 1

Answer: (B)

6.25 m

$molality=\frac{\text{moles of solute}}{\text{kilograms of solvent}}$

$\text{moles of}NaOH=\frac{\text{Weight of}NaOH}{\text{Mass of}NaOH}=\frac{25}{40}=\frac{5}{8}=0.625$

$\text{kilograms of}{H}_{2}O=\frac{\text{Weight of}{H}_{2}O}{1000}=\frac{100}{1000}=0.1$

$\therefore molality=\frac{\text{moles of solute}}{\text{kilograms of solvent}}=\frac{0.625}{0.1}=6.25m$

Hence, the correct answer is 6.25.