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Tiffany Wu 1K
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Joined: Wed Sep 21, 2016 2:56 pm


Postby Tiffany Wu 1K » Fri Sep 30, 2016 2:30 am

When calculating an empirical formula, when is it okay to round up?
For section F, number 11b in the homework problems, it asks to find the empirical formula of a compound used to generate O2 gas in a laboratory has the mass percentage composition 31.91% K and 28.93% Cl, the remainder being oxygen.
I went through the process of converting grams to moles for all 3 elements, and then dividing that by the smallest product. Oxygen came out to be 2.448, and when I looked in the answer key, it was rounded up to 3 in the empirical formula. So the empirical formula ended up being KClO3. I would've thought to multiply the products by 2, which makes it K2Cl2O5.

Alexandra Watts 3L
Posts: 14
Joined: Wed Sep 21, 2016 2:56 pm

Re: Rounding

Postby Alexandra Watts 3L » Fri Sep 30, 2016 9:14 am

When I did this problem, the number of moles I calculated for oxygen (after dividing each element's number of moles by the smallest number) was 2.99. I think you were just maybe not being exact enough in your calculations; try to write out more than 2 decimal points of the molar mass. Hope that helps!

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