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Homework Help: Molar mass problem

  1. Sep 5, 2007 #1
    1. The problem statement, all variables and given/known data

    A 2.02-g sample of an enzyme is used to make a 6.00-mL solution. What is the molar mass of the enzyme if the osmotic pressure of the solution at 298K is 0.123 atm? Note that enzymes are nonelectrolytes

    2. Relevant equations

    pi=MRT , R=.0821 L*atm*K^1-*mol^1-

    3. The attempt at a solution

    pi=MRT => pi/RT=M=.123 atm/(298K)(.0821)=.00503 M

    to find molar mass, I'd want to convert my concentration into grams/mol

    .00503 M =.00503 mmol/1 mL
    multiply (.00503 mmol/1mL)*(6.00 mL)= .0302 mmol => .00003016 mol enzyme

    so molar mass = 2.02 g enzyme /.00003016 mol enzyme = 66976. 12732 g/mol , which is unusually enormous for a typical molar mass
  2. jcsd
  3. Sep 6, 2007 #2
    I did the problem a few times and got the same answer. Althought it does seem high so I redid it a few times and kept getting the same answer. Maybe i'm missing something.
  4. Sep 6, 2007 #3


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    Homework Helper

    The answer looks right to me.
  5. Sep 7, 2007 #4


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    Gold Member

    I assume that your answer is approximately 67,000 g/mol? This is 67 kilodaltons (kDa) which is well within the usual range for an enzyme.
  6. Sep 8, 2007 #5
    i get the same, and expect big fat numbers for enzymes (as chemisttree points out)

    4 to 1 :)
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