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Homework Help: Mass Percent

  1. Sep 24, 2008 #1
    1. The problem statement, all variables and given/known data

    What volume (L) of the solvent acetone should be added to 1790 g of the solute methylene chloride to make a solution that is 20.3 g methylene chloride per 100. g solution?

    Molar Mass (g/mol)
    CH2Cl2 84.93
    (CH3)2CO 58.05
    Density (g/mL):
    CH2Cl2 1.327
    (CH3)2CO 0.7899
    methylene chloride

    2. Relevant equations

    percent by mass = mass of solute/ mass of solution x 100

    3. The attempt at a solution
    Im taking organic chem right now and this is a question for one of my chem lab homeworks so I am a little rusty with these kinds of problems...but this is where im at/stuck

    Looking for (L) of (CH3)2CO Given: 1790g CH2Cl2 and the mass percent fraction is:
    20.3g CH2Cl2/100g soln.

    I know that you have to use the densities to convert from g-->L but I just don't know how to get to that point..
  2. jcsd
  3. Sep 24, 2008 #2


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    Homework Helper
    Education Advisor
    Gold Member

    That means that you have a solution which is made of the ratio 203 parts mass methylene chloride to 797 parts mass acetone. This is based on 1000 parts mass of solution. Now, scale this up to 1790 parts mass of solution.
  4. Sep 25, 2008 #3
    ah!! yes, thank you...
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