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NEET-XII-Chemistry

02: Solutions

with Solutions - page 2
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  • #9
    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.
    digAnsr:   b
    Ans : (i) 15 ppm (by mass) means 15 parts per million (106) of the solution.
    Therefore, percent by mass
    = 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) ≈ 106 g of water.
    Molality of the solution
    = 1.26 × 10-4 m