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Recrystalization Lab

  1. Jan 21, 2007 #1
    1. The problem statement, all variables and given/known data

    You are given a mixture containing two compounds, A and B. Both compounds have a solubility of 1g/100mL of solvent at 20 degree celcius and 12g/100mL of solvent at 100 degree celcius. The sample is composed of 1.5g of A and 10g of B. At 100 degree celcius all of the sample just dissolves in a minimum amount of solvent. The solution is cooled to 20 degree celcius and crystals are collected. Calculate the composition of the crystals and the yeild of the process. What is the composition of the mother liquor?

    2. Relevant equations

    No equations.

    3. The attempt at a solution

    Compound A: 1.5g x 100mL/12g = 12.5mL
    Compound B: 10g x 100mL/12g = 83.3mL
    So from this, of the solution (solvent that just dissolves A and B), 12.5mL dissolves A and 83.8mL dissolves B.

    When cooled, the solubility is only 1g/100mL, so
    Compound A: 12.5mL x 1g/100mL = 0.125g
    Compound B: 83.3mL x 1g/100mL = 0.833g
    Therefore the crystals collected have composition:
    Compound A = 0.125g/(0.125 +0.833)g x 100% = 13.05%
    Compound B = 0.833g/(0.125 +0.833)g x 100% = 86.95%

    Does any of this make sense? If not, where did I go wrong? I'm also unsure of how to calculate the yeild of the process and the composition of the mother liquor.

    Any help is greatly appreciated. Thanks.
  2. jcsd
  3. Jan 21, 2007 #2
    You already calculated the yield when you figured out the %'s of compound A and B...as for the composition of mother liquor, I have no clue what its asking for.
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