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Thread: Calculation of molarity - please help

  1. #1 Calculation of molarity - please help 
    New Member
    Join Date
    Jul 2008
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    2
    Hi,

    I have to make up a 0.5N solution of HNO3 (69%). I have attempted to do the calculation but am not confident if it is correct. Please see below:

    no. moles = cv/1000

    c = 0.5N v = 100ml

    so no.moles = 0.5 x 100/ 1000 = 0.05 moles

    mass = 0.05moles/63 = 3.15g

    HN03 (69%) = 2.17g

    Therefore 2.17g of HNO3 (69%) in 100ml water = 0.5N

    Is this correct? (As someone else seems to have got 4.56g as the answer and I dont know where they obtained this from)

    Thank you very much for any help.


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  3. #2  
    Forum Bachelors Degree
    Join Date
    May 2007
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    NC USA
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    I did the calculations and got 4.56g.

    This is where you went wrong: 69% * 3.15g = 2.17g

    and 3.15g/69% = 4.56g.

    So you multiplied where you should have divided. Try to determine why division is needed here.


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  4. #3  
    New Member
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    Jul 2008
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    ok, thanks for your help.
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