chemistry

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500g urea aq. Sol. Has mole fraction 0.2 what is molality of sol.

  • chemistry -

    answer to how much heat is required to raise the temperature of 68.0 g of AIF3 from 25 degrees celsius to 80.0 degrees celsius

  • to lol--chemistry -

    Your question is answered above.

  • to mohit---chemistry -

    The mass of the solution is 500. How much is urea and how much is water?
    Let X = g urea
    and 500-x = grams H2O
    Then mols urea = X/60
    mol H2O = (500-X/18)

    Then
    nurea/(nurea + nH2O) = 0.2
    (X/60)/{[(X/60)] + [(500-X)/18]} = 0.2

    I solved for X and obtained about 227 g for urea and 273 g H2O. You can work that out but that's very close to a mole fraction for urea of 0.2.
    Then n urea = about 3.8
    n H2O = about 15.2

    From above we had 227 g urea (about 3.8 mols) and 273 g H2O
    molality = (mols solute)/(kg solvent)
    mols solute = about 3.8
    kg solvent = about 0.273
    m = ?
    My numbers are estimates; you should recalculate each step.

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