Calculating Molarity


by Jim4592
Tags: molarity
Jim4592
Jim4592 is offline
#1
Sep12-10, 08:40 PM
P: 49
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!
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Borek
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#2
Sep13-10, 02:22 AM
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Not bad - you are on the right track - but wrong. You have not used 43% in your calculations and this is an important information.
Jim4592
Jim4592 is offline
#3
Sep13-10, 08:27 PM
P: 49
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.

UPDATE:

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?

Borek
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#4
Sep14-10, 02:28 AM
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Calculating Molarity


Much better.


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