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NEET-XI-Chemistry

01: Some Basic Concepts of Chemistry

 page 5
Qstn# 17-i Prvs-QstnNext-Qstn
  • #17-i
    Express this in percent by mass.
    () Determine the molality of chloroform in the water sample.
    Ans : 1 ppm is equivalent to 1 part out of 1 million (106) parts.

    ∴ Mass percent of 15 ppm chloroform in water


    () 100 g of the sample contains 1.5 × 10-3 g of CHCl3.

    ⇒ 1000 g of the sample contains 1.5 × 10-2 g of CHCl3.

    ∴ Molality of chloroform in water



    Molar mass of CHCl3 = 12.00 + 1.00 + 3(35.5)

    = 119.5 g mol-1

    ∴ Molality of chloroform in water = 0.0125 × 10-2 m

    = 1.25 × 10-4 m
  • #17-ii
    Determine the molality of chloroform in the water sample.
    Ans : 100 g of the sample contains 1.5 × 10-3 g of CHCl3.

    ⇒ 1000 g of the sample contains 1.5 × 10-2 g of CHCl3.

    ∴ Molality of chloroform in water



    Molar mass of CHCl3 = 12.00 + 1.00 + 3(35.5)

    = 119.5 g mol-1

    ∴ Molality of chloroform in water = 0.0125 × 10-2 m

    = 1.25 × 10-4 m