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26 December, 06:29

Calculate the vapor pressure of a solution of 45.0 g of glycerol (c3h8o3) in 500.0 g of water at 25

c. the vapor pressure of water at 25 c is 23.76 torr.

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  1. 26 December, 06:46
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    The vapour pressure of the glycerol solution is 23.35 torr.

    Use Raoult's Law to calculate the vapour pressure:

    p_1 = χ_1p_1°

    where

    χ_1 = the mole fraction of the solvent

    p_1 and p_1° are the vapour pressures of the solution and of the pure solvent

    The formula for vapour pressure lowering Δp is

    Δp = p_1° - p_1

    Δp = p_1° - χ_1p_1° = p_1° (1 - χ_1) = χ_2p_1°

    where χ_2 is the mole fraction of the solute.

    Step 1. Calculate the mole fraction of glycerol

    n_2 = 45.0 g gly * (1 moL gly/92.08 gly) = 0.4887 mol gly

    n_1 = 500.0 g H_2O * (1 mol H_2O/18.02 g H_2O) = 27.75 mol H_2O

    χ_2 = n_2 / (n_1 + n_2) = 0.4887 / (0.4887 + 27.75) = 0.4887/28.24 = 0.017 31

    Step 2. Calculate the vapour pressure lowering

    Δp = χ_2p_1° = 0.017 31 * 23.76 torr = 0.4112 torr

    Step 3. Calculate the vapour pressure

    p_1 = p_1° - Δp = 23.76 torr - 0.4112 torr = 23.35 torr
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