Question

Elevation in the boiling point for 1 molal solution of glucose is 2K. The depression in the freezing point for 2 molal solution of glucose in the same solvent is 2K. The relation between K_b and K_f is
1. K_b = 1.5 K_f
2. K_b = 0.5K_f
3. K_b = K_f
4. K_b = 2K_f

Answer 1

Correct Answer - Option 4 : K_b = 2K_f

Concept:

Elevation in boiling point (ΔT_b) = K_b × m × i

Depression is freezing point (ΔT_f) = K_f × m × i

Where, m = molality 

For the glucose solution (Van’t Hoff factor, i = 1)

\(\Delta T_{b}^{1~m}=\Delta T_{f}^{2m}=2K\)

So, K_b × 1 × 1 = K_f × 2 × 1

⇒ K_b = 2K_f