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Homework Help: Complex molarity problem.

  1. Oct 31, 2012 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations
    The answer is B, but I would like to know how to find the answer.
    Molarity = moles * volume

    3. The attempt at a solution
    Yep, I tried for 15+ minutes and couldn't get the darn units to cancel out. A worked out solution would be very helpful.
    Last edited by a moderator: Oct 31, 2012
  2. jcsd
  3. Nov 1, 2012 #2
    Is there a reason you have provided an image, rather than text?

    How many moles of Na+ do you need?
  4. Nov 1, 2012 #3


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    Gold Member

    The relevant equation, "Molarity = moles * volume", is wrong.
  5. Nov 3, 2012 #4
    Molarity = mole per liter or mol/L

    Determine the ratio of Na+ in Na3PO4 by observing the formulas (*Hint 1/3 or 3/1). Multiply this by your Molar concentration of Na+ given in the problem.

    Next, set up a ratio of:

    [Na*(1/3 or 3/1) (M)] / Na3PO4 (M)


    Na3PO4 (M) / [Na*(1/3 or 3/1) (M)]

    (reason whether the answer should be greater than 1 or less than 1 to determine which ratio to use).

    Finally multiply this by the volume you're trying to prepare.
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