A solution of 2.50 g of a compound having the empirical formula C6H5P in 25.0 g of benzene(C6H6) is observed to freeze at 4.3 degrees C. Calculate the molar mass of the solute and its molecular formula.

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  1. I think I got the answer.

    Molar Mass = 119 g/mol

    Molecular formula is the same = C6H5P

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  2. I wonder how you came up with 119 g/mol?
    delta T = Kf*m
    5.5-4.3 = 1.2 for delta T.
    I found Kf = 4.90
    1.2 = 4.90*m
    m = 1.2/4.90 = 0.2449
    m = moles/kg solvent
    moles = m*kg solvent = 0.2449*0.025 = 0.00612 moles.
    moles = grams/molar mass or
    molar mass = grams/moles = 2.50g/0.00612 = about 400 or so. Check my work.

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