Question

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!

Answer 1

I think 2 is the right approach.
#3 can't be right since M = mols/L and this calculates mols(correctly)/10^6 grams(not L).

#1 would be right, I think, IF the 6.0 ppm was MEASURED in hexane (meaning the standards were done the same way) but apparently this is not the case. #2 starts with the right definition of
6.0 ppm = 6.0grams/1,000,000 g while #1 is not the right definition (mg/L is ok for aqueous solutions but not for hexane solution) unless the standards were in hexane also.

Answer 2

Thanks soo much! That makes sense now :)