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Homework Help: Freezing point

  1. May 17, 2010 #1
    1. The problem statement, all variables and given/known data
    A solution is made by dissolving 250.0 g of solid potassium chromate (K2CrO4) in 1.00 kg of water?
    what will be the freezing point of the new solution.



    2. Relevant equations
    [Delta]T(freezing point)=(Van't Hoff Factor)(molal concentration of solute particles)(molal freezing point-depression constant)

    Van't Hoff Factor = (moles of particles in solution/moles of solute dissolved)

    molality= moles of solute/ kg of solution

    3. The attempt at a solution
    (250 g K2CrO4)(1 mol K2CrO4/194.188 K2CrO4) = 1.29 mol of K2CrO4
    (1.29 mol K2CrO4/1.25 kg solution) = 1.0296 mol/kg
    Change in freezing point = (1.0296 molality)(1.86 degrees Celsius/molality)(3 Van't Hoff Factor)
    Change in freezing point = 0 degrees celsius - 5.750 degrees celsius
    Change in freezing point = -5.75 degrees celsius

    though the answer keys tells me its -7.18? please help me out
     
  2. jcsd
  3. May 17, 2010 #2
    1kg of solvent only, not 1.25kg
     
  4. May 17, 2010 #3
    nvm i got it
     
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