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Homework Help: How to calculate weight needed for a concentration

  1. Nov 9, 2017 #1
    • Please post this type of questions in HW section using the template and showing your work.
    I haven't had a chemistry class in many years. Recently I saw an interesting article that used a solution of resveratrol (228.25 grams per mole) in dimethylsulfoxide (78.13 grams per mole). The concentration was listed as 5 uMol.
    If I had 10 grams of DMSO how much resveratrol would I add to achieve the 5 uMol concentration? And how is this calculated? Thanks.
  2. jcsd
  3. Nov 9, 2017 #2


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    Start with the definition of molar concentration.
  4. Nov 12, 2017 #3


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    Would you be clearer about the "5 uMoL" ? What is that unit? Micro-something. Either you mean, MOLES, MICROMOLES, MICROMOLES-or-LITER, MICROMOLES PER LITER,... What?
  5. Nov 12, 2017 #4
  6. Nov 12, 2017 #5


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    Okay, micromoles per liter.
    You want 5 micromoles per liter of resveratrol. You 'have' 10 GRAMS of DMSO and you wish to find how much resveratrol is needed.

    Use x grams of resveratrol,
    d is density of dimethylsulfoxide as grams per milliliter , which you need to look-up,
    and you should fill in the unstated units of measure to be sure you see the way the two numbers work,
    and the right side is as MOLES per LITER:

    (Micro moles per liter, the same as the number shown on the right side)
    That is in plain text but you could rewrite in normal notation on paper, yourself so more understandable.
    Solve for x.

    Note: the density of DMSO is NOT 78.13 grams per mole and not moles per liter. See a handbook.

    Also, note, https://en.wikipedia.org/wiki/Resveratrol
    Last edited: Nov 12, 2017
  7. Nov 12, 2017 #6


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    I'd guess that a person should not go playing with dimethylsulfoxide without care and knowledge. Storage? Exposure? Grades of quality? Material Safety Data Sheet?
  8. Nov 12, 2017 #7
    According to Wiki, the density is almost like water at 1.1004 g cm−3.
    78.13 is the molar mass, which I thought might have been needed.
    Thanks for the formula. I will rearrange it on paper when I get a chance.
    Also good to know was that uM means micro-moles per liter. Would not have guessed that.
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