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A sample of drinking water was found to be severely contaminated with chloroform, CHCl 3 , supposed to be carcinogenic in nature. The level of contamination was 15 ppm (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).

(ii)    Determine the molality of chloroform in the water sample.

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The molarity of chloroform sample in water will be:

= \frac{number\ of\ moles\ present}{Volume\ of\ solution\ in\ L}

The molar mass of Chloroform CHCl_{3}  :

= 12+1+(3\times35.5) = 118.5g\ mol^{-1}

So we have calculated in the previous part that percentage by mass of chloroform is 1.5\times10^{-3}.

Hence in 100g sample, there will be 1.5\times10^{-3}g of chloroform.

Therefore, 1000g (1Kg) of the sample will contain choroform = 1.5\times10^{-2}g.

= \frac{1.5\times10^{-2}}{118.65\ mol} = 1.266\times 10^{-4}\ mol

Therefore, the molarity of chloroform in the water sample is 1.266\times 10^{-4}\ M.

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