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10/09/2020 8:50 pm
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A sample of drinking water was found to be severely contaminated with chloroform (CHCl3) 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.
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10/09/2020 8:53 pm
15 ppm corresponds to 15 g chloroform in 1000, 000 g of solution.
(i) Percent by mass = Mass of chloroform/Mass of solution × 100
Percent by mass = 15/1000, 000 × 100 = 1.5 × 10-3%
(ii) Molality = Mass of chloroform/Molar mass of chloroform × (Mass of solution − mass of chloroform) × 1000 (all masses in g)
Molality = 15/119.5 × (1000, 000 - 15) × 1000 = 1.255 × 10-4 m.