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# What mass of ethanol be added to 1.0Kg water to have the mole fraction of ethanol equal to 0.20?

$\begin{array}{1 1}63.89g\\6.39g\\638.89g\\683.89g\end{array}$

$0.2=\large\frac{m/46gmol^{-1})}{(m/46gmol^{-1})+(1000g/18gmol^{-1})}$
$\Rightarrow \large\frac{m}{46g}=\frac{0.2\times 1000}{18}\times \frac{1}{0.8}$$=13.89$
$m=13.89\times 46g=638.89g$