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Homework Help: Dilutions question

  1. May 3, 2009 #1
    1. The problem statement, all variables and given/known data
    To what volume shuould you dilute 125 mL of an 8.00 mL CuCl2 solution so that 50.0 mL of the diluted solution contains 5.9 g CuCl2?

    2. Relevant equations

    M= mol solute / vol solution (L)
    m = mol solute / mass solvent (kg)
    mole percent = mol solute / mol solute + solvent

    3. The attempt at a solution
    8.00 M = mol CuCl2 / .125 L
    1 mol CuCl2 x (65.55 + 2(35.45)g / 1 mol CuCl2 = 134.45 g CuCl2
    5.9 g CuCl2 (final) x (1 mol CuCl2) / (65.55 +2(35.45)g = .4388 mol CuCl2
    8.00 M = .44 mol CuCl2 --> .055 L solution???????????
    I don't know how to use these formulas to find the diluted amount using the old amount? Do I subtract the grams CuCl2 to the new Molarity and find the tot vol? The answer is not the same as the back of the book.
  2. jcsd
  3. May 3, 2009 #2


    User Avatar

    Staff: Mentor

    How many moles of CuCl2 do you have?

    What molarity do you need?

  4. May 10, 2009 #3
    Vapor Pressure Problem

    An aq CaCl2 colution has a vapor pressure of 81.6 mmHg at 50 degrees C. The vapor pressure of pure water at this temperature is 92.6 mmHg. What is the concentration of CaCl2 in mass percent?

    I don't even know where to start, if I can use Raoult's Law or not . . .
  5. May 10, 2009 #4


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    Staff: Mentor

    You can. Just assume that whatever is dissolved has a vapor pressure of zero.
  6. May 11, 2009 #5
    The question doesnt even make any sense.

    you have 0.125dm3 of 8 molar CuCl2 and you want to turn it into 0.050dm3 of CuCl2?
  7. May 11, 2009 #6
    is the answer 9.09m3?

    im guessing its a typo and you have 8 molar CuCl2 you need to dilute it so that 0.050dm3 has 0.044moles.

    divide 8 moles with 0.044 and you get 181.81 then divide that with 0.050.
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