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12 March, 19:57

Calculate the vapor pressure of water above a solution prepared by dissolving 28.5 g of glycerin (c3h8o3) in 135 g of water at 343 k. (the vapor pressure of water at 343 k is 233.7 torr.)

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  1. 12 March, 20:20
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    dа ta:

    Solute: 28.5 g of glycerin (C3H8O3)

    Solvent: 135 g of water at 343 k.

    Vapor pressure of water at 343 k: 233.7 torr.

    Quesiton: Vapor pressure of water

    Solution:

    Raoult's Law: The vapour pressure of a solution of a non-volatile solute is equal to the vapour pressure of the pure solvent at that temperature multiplied by its mole fraction.

    Formula: p = Xsolvent * P pure solvent

    X solvent = moles solvent / moles of solution

    molar mass of H2O = 2*1.0g/mol + 16.0 g/mol = 18.0 g/mol

    moles of solvent = 135 g of water / 18.0 g/mol = 7.50 mol

    molar mass of C3H8O3 = 3*12.0 g/mol + 8*1 g/mol + 3*16g/mol = 92 g/mol

    moles of solute = 28.5 g / 92.0 g/mol = 0.310 mol

    moles of solution = moles of solute + moles of solvent = 7.50mol + 0.310mol = 7.810 mol

    Xsolvent = 7.50mol / 7.81mol = 0.960

    p = 233.7 torr * 0.960 = 224.4 torr

    Answer: 224.4 torr
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