A 1 molal \(\mathrm{K_4Fe(CN)_6}\) solution has a degree of dissociation of 0.4. Its boiling point is equal to that of another solution which contains 18.1 weight percent of a non electrolytic solute A. The molar mass of A is __________ u. (Round off to the Nearest Integer). [Density of water = 1.0 g cm\(-3\) ]
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Correct Answer: 85
Solution and Explanation
i = 1 + (n - 1)\(\alpha\) = 1 + 4(0.4) = 2.6
For the electrolyte: \(\Delta T_b = i K_b m = 2.6 \times K_b \times 1 = 2.6K_b\).
For solution of A: 18.1 g of A in 81.9 g of water, so molality = \(\frac{18.1/M}{81.9/1000} = \frac{221.0}{M}\).
Equal boiling points give equal \(\Delta T_b\): \(2.6K_b = K_b \times \frac{221.0}{M}\)
\(M = \frac{221.0}{2.6} = 85.0\) u
Answer: 85
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