A sample of drinking water was found to be severely contaminated with chloroform, CHCl3, supposed to be carcinogenic in nature. The level of contamination was 15 ppm (by mass).
(i) Express this in percent by mass.
(ii) Determine the Molality of chloroform in the water sample.
Given:
Level of contamination = 15 ppm [by mass]
To find: Mass Percentage and Molality
Formula:
Molality 
Mass Percentage of Solute
Calculation of Mass Percentage:
15 ppm means 15 parts of Chloroform in 1 million [106] parts of drinking water
→Mass Percentage 
= 1.5 × 10-3 %
Calculation of Molality:
→Molecular Mass of Chloroform, CHCl3 = [12] + [1] + [35.5×3]
= 119.5 g
→Number of Moles of Chloroform = [15 / 119.5]
= 0.1255 moles
Molality 
= 1.255 × 10-4
Therefore, the Mass Percentage is = 1.5 × 10-3% and the Molality of the solution is = 1.255 × 10-4 m.