Question

A sample of drinking water was found to be severely contaminated with chloroform, `CHCl_(3)`, supposed to be 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

Percentage (%) by mass of `CHCI_(3)`
`=("Mass of"CHCI_(3))/("Mass of solution")xx100=((15.0g))/((10^(6)g))xx100 = 1.5xx10^(-3)`
Molality of solution
Mass of solute= 15 g, Mass of solution= `10^(6)`g
"Mass of water" = `(10^(6)-15)~~10^(6)g`.
`"Molality of solution (m)" = (("Mass of"CHCI_(3))/("Molar mass"))/("Masss of water in kg")=(15g)/((119.5mol^(-1))/((10^(6)//1000 kg)))`
=`1.25xx10^(4)mol kg^(-1)=1.25xx10^(-4)m`