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Find the molecular mass of a solute by freezing point depression. Solvent: para-dichlorobenzene Freezing point of pure solvent: 53.02C Mass of unknown substance: 2.04g Freezingpointdepressin constant:7.1c/m Mass of para-dichlo...: 24.80g Freexing point solution: 50.78 C Can you explain how you got it, Please and thank you

  • ap chem -

    delta T = Kf*molality.
    Calculate molality.

    molality = moles/kg solvent.
    Calculate moles.

    moles = grams/molar mass.
    Calculate molar mass.

  • ap chem -

    260.73 g/mol

    Temp of solvent - Temp of solution = constant x molality

    solve for molality.
    molality = mol of solute/kg of solvent

    molality = change in Temp/constant

    molality = (53.02-50.78)/7.1 = 0.3155 mol/kg

    Convert to mol/g, so divide by 1000g.

    molality = 3.155e-4 mol/g

    multiply molality by grams of solvent to get moles of solute.

    3.155e-4 mol/g x 24.8 g = 0.007824 mol

    Now you have moles of solute. Solve for molecular mass by diving the grams of the solute by the calculated moles of solute.

    Molecular mass of solute = 2.04 g/0.007824 mol = 260.73 mol/g of solute.

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