Question

1 molal aqueous solution of an electrolyte A$_3$B$_3$ is 60% ionised. The boiling point of the solution at 1 atm is __________ K. [Given $K_b$ (H$_2$O) = 0.52 K kg mol$^{-1}$, $T_b$ pure water = 373.15 K]

Hint:

The Van't Hoff factor ($i$) accounts for the increased number of particles in solution due to dissociation. Boiling point always {elevates} in the presence of a non-volatile solute.

Answer 1

Correct Answer: 375

Step 1: For $A_3B_3 \rightarrow 3A + 3B$, total ions $n = 6$.
Step 2: Van't Hoff factor $i = 1 + \alpha(n-1) = 1 + 0.6(6-1) = 1 + 3.0 = 4.0$.
Step 3: $\Delta T_b = i \times K_b \times m = 4.0 \times 0.52 \times 1 = 2.08$ K.
Step 4: $T_b = 373.15 + 2.08 = 375.23$ K $\approx 375$ K.