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Homework Help: Percentage Weight Question

  1. Sep 19, 2009 #1
    1. The problem statement, all variables and given/known data
    You have a 20% w/v stock solution of a sugar of molecular weight 160 Daltons. How much of this stock solution will you need to use to...

    a. prepare 10 ml of solution at 350 mg sugar per ml.

    b. 7 ml of solution containing 15 micromoles of sugar

    2. Relevant equations

    3. The attempt at a solution

    a) So 20% w/v stock solution = 0.2 g/mL

    350 mg/mL x 10mL gives us 3500mg of the sugar, or 3.5g

    so the amount of solution we want is

    x mL = 3.5 g / (0.2g / mL) = 17.5mL ( is this correct?)

    b) 5umol = 1.5 x 10^-5 mol

    1.5 x 10^-5 mol (160 Daltons / 1mol) = 2.4 x 10^-3 g

    (2.4 x 10^-3g) / 7mL = 4.89 x 10^-5 g/mL

    and then I am stuck. How are you supposed to make 4.89 x 10^-5g/mL solution from a 0.2g/mL stock solution?

    thank you in advance
  2. jcsd
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