1.

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.

Answer»

15 ppm means 15 parts in million (106) parts by mass in solution 

∴ % by mass = \(\frac{15}{10^6}\) × 100 = 15 × 10-4 

Taking 15 g chloroform in 106

Molar mass of CHCl3 = 12 + 1 + 3 × 35.5 = 119.5 g mol-1 

Molality = \(\frac{\frac{15}{119.5}}{10^6}\) × 1000 = 1.25 × 10-4 m



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