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A solution containing,8g of a substance in 100g of diethyl ether boils at $36.86^{\large\circ}C$,whereas pure ether boils at $35.60^{\large\circ}C$.Determine the molecular mass of the solute.(For ether $K_b=2.02kg mol^{-1})$

$\begin{array}{1 1}128.25gmol^{-1}\\138.25gmol^{-1}\\148.25gmol^{-1}\\168.25gmol^{-1}\end{array} $

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We have,
Mass of solute $W_2=8g$
Mass of solvent,$W_1=100g$
Elevation of boiling point,$\Delta T_b=36.86-35.60$
$\Rightarrow 1.26^{\large\circ}C$
Molecular mass of solute $M_2=\large\frac{1000\times W_2\times K_b}{\Delta T_b\times W_1}$
$\Rightarrow \large\frac{1000\times 8\times 2.02}{1.26\times 100}$
$\Rightarrow \large\frac{161.6}{1.26}$
$\Rightarrow 128.25 g mol^{-1}$
answered Aug 8, 2014 by sreemathi.v

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