A sample of drinking water was found to be severely contaminated with chloroform $ \left(\mathrm{CHCl}_{3}\right) $ supposed to a 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.

Question

A sample of drinking water was found to be severely contaminated with chloroform $ \left(\mathrm{CHCl}_{3}\right) $ supposed to a 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., $ 1.25 \times 10^{-4} \mathrm{~m} $, $ 2.41 \times 10^{-4} \mathrm{~m} $, $ 4.85 \times 10^{-6} \mathrm{~m} $, $ 6.45 \times 10^{-8} \mathrm{~m} 6.45 \times 10^{-8} \mathrm{~m} $

MARKS App · Accepted Answer

i Percentage % by mass of CHCl 3 = mass of CHCl 3 Mass of solution × 100 = 15.0 g 10 6 g × 100 = 1.5 × 10 - 3 % ii Molality of solution (m) = Mass of CHCl 3 / Molar mass Mass of water in kg = 1 5 / 1 2 + 1 + 106.5 10 6 / 1000 kg = 15 g 119.5 g mol - 1 × 1000 10 6 kg = 1 . 25 × 10 - 4 mol Kg - 1 = 1 . 25 × 10 - 4 m .

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