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Homework Help: Calculate the molarity

  1. Feb 14, 2005 #1

    DB

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    Havin a little trouble:
    Calculate the molarity of 29.25 g of NaCl dissolved in 700ml of total solution in moles per litre.

    I know that 1 mol of salt is 57 g so 29.25 g of salt is ~0.51 mol...
    But then what?
    Is the answer ~0.35 mol/700L ? I cross multiplied.

    Thanks
     
  2. jcsd
  3. Feb 14, 2005 #2

    dextercioby

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    No.The molar mass of NaCl is 56.5.You'll have to figure out how many moles that means and then apply the simple rule:
    x moles------------>700mL
    y moles------------>1000mL

    Daniel.

    P.S."y" is the one you're interested in.
     
  4. Feb 14, 2005 #3

    DB

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    ~0.357 mol/L?
     
  5. Feb 14, 2005 #4

    dextercioby

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    What is the value of "x" that u found...?

    Daniel.
     
  6. Feb 14, 2005 #5

    DB

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    i got ~0.51 moles by dividing 29.25 by 56.5, the i cross multiplied knowing x.
     
  7. Feb 14, 2005 #6

    dextercioby

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    And u wound up with ~0.36,huh...?You didn't do it (the cross multiplication) correctly,after all,at constant concentration,the more sollution u have (1000mL cf.700mL),the more dilluted substance u must have,right??

    Daniel.
     
  8. Feb 14, 2005 #7

    DB

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    O i was so hooked on dilution! is the answer ~0.72 mol/L???
     
  9. Feb 14, 2005 #8

    dextercioby

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    Yes,pretty much so.

    Daniel.
     
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