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)
(i) express this in percentage by mass
(ii) determine the molality of chloroform in the water sample.

Explanation

(i) 15 ppm means 15 parts in million `(10^(6))` parts by mass in the solution
`therefore %` of mass `= (15)/(10^(6) xx 100 = 1.5 xx 10 ^(-4)`
(ii) 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 xx 35.5) = 119.5 g mol^(-1)`
`therefore` Molality `= ((15)/(119.5))/(10^(6)) xx 100 = 1.25 xx 10 ^(-5)m`