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April 26, 2015

Homework Help: Chemistry

Posted by Just One Stranger on Thursday, December 6, 2012 at 4:50am.

So my chem experiment asks us: What is the molarity of a 6.0 ppm solution (it's a 6.0 ppm chlorophyll solution, hexane is the solvent)

Now, I've found a few ways to solve for it but they both give me different values. If it's possible, could you just tell me which is right.

#1 Way:
6parts/1million --> 0.006g/L -->
take 0.006g convert w/ molar mass chlorophyll (1 mole/ 893.49 g) --> 6.71524 *10^(-6) moles
put 6.71524 *10^(-6) over 1L --> 6.71524 *10^(-6) M

0R
6parts/1million --> 6g/1000,000g -->
take 6g convert w/ molar mass chlorophyll (1 mole/ 893.49 g) --> 6.71524 *10^(-3) moles
use hexane's density to convert 1000,000g to (mL first then) L (density: 1mL/0.6548g) --> 1527.18388 L
put 6.71524 *10^(-3) moles over 1527.18388 L --> 4.397*10^(-6) M

OR
6parts/1million -->6g/1000,000g
take 6g convert w/ molar mass chlorophyll (1 mole/ 893.49 g) --> 6.71524 *10^(-3) moles
put 6.71524 *10^(-3) moles over 1000,000 --> 6.71524 *10^(-9) M

I think the second one is the right one but I'm not sure. Could you please help me? Thanks!

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