A solution of a non-volatile solute in ethanol (B.P of ethanol = 78.4°C) has a vapour pressure of 730 mm of Hg at 78.4°C. To what temperature, the above solution must be heated have the pressure of 760mm of Hg? K_b of ethanol = 1.22 k Kg mol^–1. Express temperature of 10x. x is __

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answer is 8.

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Detailed Solution

$\begin{array}{l} \frac{P^{0} - P}{P^{0}} = molality \times \frac{M_{B}}{1000} = \frac{m \times M_{B}}{1000} \\ \frac{760 - 730}{760} = m \times \frac{46}{1000}; m = \frac{3000}{76 \times 46} = 0 .85 \\ {ΔT}_{b} = K_{b} \times m \Rightarrow {ΔT}_{b} = 1 .22 \times 0 .85 = 1 {.04}^{0} K \\ t_{s} = 78 .4 + 1 .04 = 79 .44; 10 x = 80 \Rightarrow x = 8 \end{array}$