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Percent by mass concentration

  1. Jan 8, 2009 #1
    % by mass concentration

    1. The problem statement, all variables and given/known data

    An aqueous CaCL2 solution has a vapor pressure of 80.8mmHG at 50 degree C . The vapor pressure of pure water at this temperature is 92.6 mmHG .

    What is the concentration of CaCl2 in mass percent?

    2. Relevant equations

    % by mass = mass solute/mass solution.

    3. The attempt at a solution

    I tried converting the pressure into moles then dividing the moles of CaCl2 by the total moles. Im pretty stuck..

    Thanks
    Skadoo!
     
  2. jcsd
  3. Jan 8, 2009 #2

    Borek

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    Staff: Mentor

    Re: % by mass concentration

    Do you know Raoult's law?
     
  4. Jan 8, 2009 #3
    Re: % by mass concentration

    yeah i do. p = pa*xa+pb*xb correct? not sure how to solve for the x's....
     
  5. Jan 8, 2009 #4

    Borek

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    Staff: Mentor

    Re: % by mass concentration

    xa+xb=1
     
  6. Jan 9, 2009 #5
    Re: % by mass concentration

    alright knowing this, i use 'a' as the vap press for cacl2 and 'b' for vap press of water? then use molecular weights to to solve for total mass of solution..?
     
  7. Jan 9, 2009 #6

    Borek

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    Staff: Mentor

    Re: % by mass concentration

    Sounds OK. Don't forget CaCl2 is dissociated.
     
  8. Jan 9, 2009 #7
    Re: % by mass concentration

    ah right, almost forgot. Ill give this a run thanks.
     
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