Question

QUESTION 2.9(i)

A sample of drinking water was found to be severely contaminated with chloroform $\left(CHC{l}_3\right)$ supposed to a carcinogen. The level of contamination was 15 ppm (by mass):

(i) Express this in per cent by mass.

(ii) Determine the molality of chloroform in the water sample.

Answer 1

(i) Percentage $\left(\%\right)$ by mass of $CHC{l}_3$
$=\frac{MassofCHC{l}_3}{Massofsolution}\times 100=\frac{\left(15.0\right)}{\left({10}^{6}g\right)}\times 100=1.5\times {10}^{-3}\%$

(ii) Molality of solution (m) $=\frac{\frac{MassofCHC{l}_3}{Molarmass}}{Massofwaterinkg}$

$=\frac{\frac{15}{(12+1+106.5)}}{\frac{{10}^6}{1000kg}}$

$=\frac{\left(15g\right)}{\left(119.5gmo{l}^{-1}\right)}\times \frac{1000}{{10}^{6}kg}$

$=1.25\times {10}^{-4}molk{g}^{-1}$

$=1.25\times {10}^{-4}m$