Question

A sample of drinking water was found to be severely contaminated with chloroform $\left(\text{CHC}{\text{l}}_{\text{3}}\right)$ supposed to be a carcinogen. 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.
What role does the molecular interaction play in a solution of alcohol and water?

Answer 1

i) 15 ppm means : 15 parts per million(10⁶) of the solutions

So, Percent by mass = (mass of chloroform / total mass) x 100

= (15 / 10⁶) x 100

= 1.5 x 10^-3 %

ii) Molality Mass of chloroform = 15 g

Molar mass of chloroform (CHCl₃) = 1 × 12 + 1 × 1 + 3 × 35.5

= 119.5 g mol ^{- 1}

Moles of chloroform = 15 / 119.5 = 0.1255 mol

Mass of water = 10⁶

Therefore molality = (moles of chloroform / mass of water ) x 1000

= (0.1255 / 10⁶) x 1000

= 1.255 x 10^-4 m