Question

A sample of drinking water was found to be severely contaminated with chloroform (CHCI₃) supposed to be a carcinogen. The level of contamination was 15 ppm (by mass)

1. express this in percentage by mass 

2. determine the molality of chloroform in the water sample.

Answer 1

1. 15 ppm means 15 parts in million (10⁶ ) parts by mass in the solution 

% of mass = \(\frac{15}{10^6}\) x 100 = 1.5 x 10^-4

2. Taking 15g chloroform in 10⁶ g of the solution 

Mass of the solvent = 10⁶ g 

Molar mass of CHCl₃ = 12 + 1 + (3 x 35.5) = 119.5 g mol^-1