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Chemistry Problem

  1. Sep 26, 2007 #1
    [SOLVED] Chemistry Problem

    The question is
    Calculate the mass of pure Na2CO3 needed for the preparation of 250.00mL of a 0.005M standard carbonate solution.

    when it says PURE Na2CO3, what molarity does it mean? is it 1M??

    my guess is to use M1V1 = M2V2 to solve
    my final volume is 250mL
    final concentration is 0.005 M
    and if the pure Na2CO3 means 1M then that would be what i would be using as my stock right? then i would solve for the volume of that stock i need. After that I would use the density of Na2CO3 to find the mass

    is that right?
     
  2. jcsd
  3. Sep 26, 2007 #2

    chemisttree

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    Find out how many moles of sodium carbonate you will need to make up this solution.
    Hint: #moles = molarity(moles/L)/volume(L)
     
  4. Sep 26, 2007 #3
    so I figured that I will need 0.005M/0.25L = 0.02 mol of carbonate

    now I use the molar mass of sodium carbonate to find the mass ??
     
  5. Sep 26, 2007 #4
    yes, correct.
     
  6. Sep 26, 2007 #5
    Thanks!
     
  7. Sep 27, 2007 #6
    wait.. i thought molarity is found by (mol/L) x L?
    and not (mol/L) / L


    ????
     
  8. Sep 27, 2007 #7
    i mean moles is found by (mol/L) x L
     
  9. Sep 27, 2007 #8

    chemisttree

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    What is your question?
     
  10. Sep 27, 2007 #9
    before, you said that #moles = molarity(moles/L)/volume(L)

    i thought #moles = molarity(moles/L) x volume(L)??
     
  11. Sep 28, 2007 #10
    higherme you are correct, Molarity = mol/L;
    so mol = M x L

    probably a typo in the reply before. then multiply by Molar mass to get grams
     
  12. Sep 28, 2007 #11

    chemisttree

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    Yes higherme, you are correct. Definitely a 'typo' (screwup) on my part...
     
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