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Mass calculation

Posted: Tue Oct 02, 2018 5:28 pm
by melissa_dis4K
On the video module under Empirical and Molecular formulas, the example of finding the molecular formula for vitamin C, the molar mass given for the compound is 176.14gmol^-1. Then I take the empirical formula C3H4O3 and multiply it by 2.000 to get the molecular formula C6H8O6. What I am confused on is that in the video Professor Lavelle says that we can check the molar mass by taking the molecular formula and adding up what it would weigh if we had one mole of this compound. So, doing (6 C x 12.01g) + (8 H x 1.008) + (6 O x 16) should equal the given molar mass (176.14gmol^-1). But, when I do it, I get 176.124. Does this have to do with significant figures or is he rounding to get 176.14?

Re: Mass calculation

Posted: Tue Oct 02, 2018 6:24 pm
by Katie Frei 1L
I was curious about this too, because when I checked the molar mass I found it to be 176.12 gmol^-1. I believe the empirical formula is accurate even though the molar mass calculated is .02 off of the 176.14gmol^-1 given. I do not think it has to do with significant figures, but I would appreciate hearing the point of view of others on this problem.

Re: Mass calculation

Posted: Tue Oct 02, 2018 6:31 pm
by 804991762_4A
It does not have to deal with sig figs. I'm pretty sure it has to do with how you input the atomic mass, such as for Oxygen he rounded 15.9994 to 16. Since he rounded the atomic mass it could be the reason for his answer to b slightly different from yours.