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Calculating Molarity

  1. Sep 12, 2010 #1
    1. The problem statement, all variables and given/known data
    Eighty-six proof whiskey is 43 percent ethyl alcohol, CH3CH2OH, by volume. If the density of ethyl alcohol is 0.79 kg/L, what is the molarity in whiskey.

    2. Relevant equations
    Molar Mass of CH3CH2OH = 46.07 g

    3. The attempt at a solution

    0.79 kg/L * 1000 g/kg * 1 mole / 46.07 g = 17.15 M

    I was just looking for a check on this particular problem since I haven't taken a chemistry course since my freshman year ha!
  2. jcsd
  3. Sep 13, 2010 #2


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    Staff: Mentor

    Not bad - you are on the right track - but wrong. You have not used 43% in your calculations and this is an important information.
    Last edited by a moderator: Aug 13, 2013
  4. Sep 13, 2010 #3
    I thought you would have to use that 43% in there somewhere, but I'm not sure how to use it. It would be nice if I still owned my chem book.


    Ok I tried re-working the problem again, here's what I came up with:

    0.79 kg/L * 0.43 L / 1 L * 1000 g / 1 kg * 1 mol / 46.07 g = 7.37 M

    how does that look?
    Last edited: Sep 13, 2010
  5. Sep 14, 2010 #4


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    Staff: Mentor

    Much better.
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