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03/01/2022 3:08 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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03/01/2022 3:14 pm
(i) 15 ppm (by mass) means 15 parts per million (106) of the solution.
Therefore, percent by mass = \(\frac{15}{10^6}\) x 100%
= 1.5 × 10-3%
(ii) Molar mass of chloroform (CHCl3) = 1 × 12 + 1 × 1 + 3 × 35.5
= 119.5 g mol-1
Now, according to the question,
15 g of chloroform is present in 106 g of the solution.
i.e., 15 g of chloroform is present in (106 - 15) x 106 g of water.
∴ Molality of the solution = \(\frac{\frac{15}{119.5}mol}{10^6 \times 10^{-3}\;kg}\)
= 1.26 × 10-4 m