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# A 4% solution of sucrose is isotonic with 3% solution of an unknown organic substance.Calculate the molecular mass of unknown substance .

$\begin{array}{1 1}256.5gmol^{-1}\\156.5gmol^{-1}\\356.5gmol^{-1}\\456.5gmol^{-1}\end{array}$

Can you answer this question?

$M_{sucrose}=M_{unknown}$
$\large\frac{4}{342}\times \frac{1000}{100}=\frac{3}{x}\times \frac{1000}{100}$
$x=\large\frac{3\times 342}{4}$
$\;\;\;=\large\frac{3\times 171}{2}$
$\;\;\;=256.5gmol^{-1}$
answered Aug 8, 2014