## Questions F11

Or Fisher 1I
Posts: 35
Joined: Fri Feb 02, 2018 3:00 am

### Questions F11

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
Posts: 49
Joined: Tue Nov 14, 2017 3:01 am

### Re: Questions F11

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
Posts: 34
Joined: Wed Nov 15, 2017 3:01 am
Been upvoted: 1 time

### Re: Questions F11

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
Posts: 34
Joined: Fri Apr 06, 2018 11:01 am

### Re: Questions F11

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.

Chem_Mod
Posts: 18879
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 714 times

### Re: Questions F11

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.