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Homework Help: Osmotic Pressure/ Gen chem 2

  1. Jul 14, 2011 #1
    Human blood gives rise to an osmotic pressure of approximately 7.7 atm at body temperature, 35.9 Celsius.

    What must the molarity of an intravenous glucose solution be to give rise to the same osmotic pressure as blood?


    I use the equation ; P=MRT if that's right
    R is constant= .0821
    T= 308.9 Kelvin
    P=7.7 atm
    M= ???

    So would i rearrange the equation to P/RT=M
    I get the wrong answer tho, and the answer doesn't sound right. I know I'm doing something wrong.
  2. jcsd
  3. Jul 15, 2011 #2
    What answer did you get, and how do you know it is wrong?

    One thing: R is not 0.0821. It is 0.0821 L atm K^−1 mol^−1. Never let your numbers go out naked. Units are really, really important.
  4. Jul 17, 2011 #3
    What answer did you get, and how do you know it's wrong?
  5. Jul 17, 2011 #4
    .303 M

    and masteringchemistry says it's wrong...
  6. Jul 17, 2011 #5
    Well, what you're doing looks right to me, and that answer is at least close to the correct concentration for isotonic glucose. All I can guess is that you need to have more or fewer sig figs, or maybe different units (e.g. 303 mM), or something like that.
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