Question

Calculate the molality of the solution containing nonvolatile solute if boiling point elevation of solution is 0.39 K .

[ \(\mathrm{K}_{\mathrm{b}}\) of water \(=0.52 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}\) ]

• A. \(0.52\text{ }\mathrm{mol}\text{ }\mathrm{kg}^{-1}\)
• B. \(0.65\text{ }\mathrm{mol}\text{ }\mathrm{kg}^{-1}\)
• C. \(0.75\text{ }\mathrm{mol}\text{ }\mathrm{kg}^{-1}\)
• D. \(0.86\text{ }\mathrm{mol}\text{ }\mathrm{kg}^{-1}\)

Hint:

Use the boiling point elevation relation to get molality directly.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
Elevation of boiling point is \(\Delta T_b = K_b \times m\).

Step 2: Rearrange
\(m = \dfrac{\Delta T_b}{K_b}\).

Step 3: Calculation
\(m = \dfrac{0.39}{0.52} = 0.75\text{ mol kg}^{-1}\).

Final Answer:
The molality is 0.75 mol per kg. \[ \boxed{\text{(C) }0.75\text{ mol kg}^{-1}} \]