NCERT Class XI Chemistry Some Basic Concepts of Chemistry Solutions

Question : 17

Total: 36

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 per cent by mass.
(ii) Determine the molality of chloroform in the water sample.

Solution:

(i) 15 ppm means 15 parts in million (106) parts
% by mass =

106

× 100 = 15 × 10−4 = 1.5 × 10−3 %
(ii) Molality of CHCl3 =

1.5×10−3

100

1000

119.5

[Since Mass CHCl3 = 12 + 1 + 3535 × 3 = 119.5]
= 0.125 × 10−3 = 1.25 × 10−4 m

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