1.17. 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.
1.17. 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.
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1 Answer
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1.17. 15 ppm means 15 parts per million i.e.15 in 106
So, % by mass = 15/106 x 100 = 15 x 10-4 = 1.5 x 10-3%
Molality = No. of moles of solute/Mass of solvent in kg
Percent by mass = 1.5 x 10-3 % means 100 g of the sample contain 1.5 x 10-3 g chloroform.
So, 1000 g or 1 kg of the sample will contain 1.5 x 10-3 x 1000/100 = 1.5 x 10-2 g chloroform.
Molar mass of chloroform = 12 + 1 + (3 x 35.5) = 119.5 g/mol
Therefore, molality = 1.5 x 10-2 /119.5 = 1.26 x 10-4m.
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