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NEET-XII-Chemistry

02: Solutions

with Solutions - page 3
Qstn# B-18 Prvs-QstnNext-Qstn
  • #18
    Calculate
    the mass of a non-volatile solute (molar mass 40 g mol-1)
    which should be dissolved in 114 g octane to reduce its vapour
    pressure to 80%.
    Ans : Let the vapour pressure
    of pure octane be
    Then, the vapour
    pressure of the octane after dissolving the non-volatile solute is
    Molar mass of solute, M2 = 40 g mol-1
    Mass of octane, w1 = 114 g
    Molar mass of octane,
    (C8H18), M1 = 8 × 12 +
    18 × 1
    = 114 g mol-1
    Applying the relation,

    Hence, the required
    mass of the solute is 8 g.