Question

A solution of non volatile solute has boiling point elevation \(0.70\) K if \(K_b\) for the solvent is \(2.44 \text{K kg mol}^{-1}\). What is the molality of the solution?

• A. \(3.48\) m
• B. \(2.86\) m
• C. \(0.286\) m
• D. \(0.0186\) m

Hint:

Use delta Tb = Kb times molality.

Answer 1

The Correct Option is C

Step 1: Approach:
Elevation per unit molality is $K_b = 2.44$ K per mol/kg. So the number of molal units equals the observed elevation divided by this.

Step 2: Division:
$0.70 \div 2.44 \approx 0.287$, which rounds to the 0.286 m given in option (C).

Step 3: Rejecting Others:
Option (A) divides the other way round. Option (B) is 10 times (C). Option (D) is far too small. Answer (C).

Final Answer:
Option (C). \[ \boxed{\text{(C) } 0.286\ \text{m}} \]