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NEET-XII-Chemistry

02: Solutions

with Solutions - page 3
Qstn# B-17 Prvs-QstnNext-Qstn
  • #17
    The
    vapour pressure of water is 12.3 kPa at 300 K.
    Calculate vapour pressure of 1 molal solution of a non-volatile
    solute in it.
    Ans : 1 molal solution means 1 mol of the solute is present in 1000 g of the solvent (water).
    Molar mass of water = 18 g mol-1
    Number of moles present in 1000 g of water
    = 55.56 mol
    Therefore, mole fraction of the solute in the solution is
    .
    It is given that,
    Vapour pressure of water, = 12.3 kPa
    Applying the relation,

    ⇒ 12.3 - p1 = 0.2177
    ⇒ p1 = 12.0823
    = 12.08 kPa (approximately)
    Hence, the vapour pressure of the solution is 12.08 kPa.