Questions F11

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Or Fisher 1I
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Questions F11

Postby Or Fisher 1I » Thu Apr 05, 2018 2:52 pm

In question F11 in part c it asks to determine the mass percentage composition: 12.2% N, 5.26% H, 26.9% P, and 55.6% O. When I solved for the moles of O I got 55.6g/16.00gmol=3.48 mol because the number with the least significant figures is 3, but the solutions manual says 3.475 mol. Is this an error or am I doing something wrong?

Jocelyn Fermin1J
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Re: Questions F11

Postby Jocelyn Fermin1J » Thu Apr 05, 2018 3:36 pm

Hi, you are on the right track you just rounded the molar mass of Oxygen (15.999 to 16.00) IF you calculate 55.6g/15.999gmol=3.475 mols.

Beverly Shih 1K
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Re: Questions F11

Postby Beverly Shih 1K » Fri Apr 06, 2018 1:42 pm

I was confused about this too. Since the mass percent compositions and mass of O2 are given to 3 sfs, wouldn't the answer have to have 3 sfs, not 4?

Amir Akhavan 1E
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Re: Questions F11

Postby Amir Akhavan 1E » Sun Apr 08, 2018 3:41 pm

I also think the answer should have only three significant figures instead of four. However, the professor said significant figures would not be counted on the first exam yet.

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Re: Questions F11

Postby Chem_Mod » Sun Apr 08, 2018 3:51 pm

Based on the math you provide, it should be 3 significant figures, irrelevant of what value you use for the molar mass of oxygen atom.

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