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# A sample of drinking water was found to be severely contaminated with chloroform $(CHCl_3$) supposed to be a carcinogen. The level of contamination was 15 ppm (by mass): determine the molality of chloroform in the water sample.

$\begin{array}{1 1}1.25\times 10^{-4}m\\2.25\times 10^{-4}m\\3.25\times 10^{-4}m\\0.25\times 10^{-4}m\end{array}$

Taking 15 g chloroform in $10^6$ g of the solution.Mass of the solvent =$10^6$g
Molar mass of $CHCl_3=12+1+3\times 35.5$
$\Rightarrow 119.5gmol^{-1}$
Molality =$\large\frac{15/119.5}{10^6}$$\times 1000$
$\Rightarrow 1.25\times 10^{-4}m$