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NEET-XII-Chemistry

02: Solutions

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  • #4
    Calculate the mass of urea (NH2CONH2)
    required in making 2.5 kg of 0.25 molal aqueous solution.
    Ans : Molar
    mass of urea (NH2CONH2)
    = 2(1 × 14 + 2 × 1) + 1 × 12 + 1 × 16
    = 60
    g mol-1
    0.25
    molar aqueous solution of urea means:
    1000 g of
    water contains 0.25 mol = (0.25 × 60)g of urea
    = 15 g of
    urea
    That is,
    (1000
    + 15) g of solution contains 15 g of urea
    Therefore,
    2.5 kg (2500 g) of solution contains
    = 36.95 g
    =
    37 g of urea (approximately)
    Hence,
    mass of urea required = 37 g
    Note: There is a slight variation in this answer and the one given in the
    NCERT textbook.