F5: Problem deciding significant figures

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mhuang 1E
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Joined: Fri Sep 29, 2017 7:05 am

F5: Problem deciding significant figures

Postby mhuang 1E » Wed Oct 04, 2017 11:43 pm

Hi!

I'm having some problem deciding/knowing how many significant figures to use for each problem. For example, in F5, the solutions manual shows that the mass percentage composition for C is 52.15%, while the mass percentage composition for H is 9.3787%. Could anyone explain why the answer for H calls for more significant figures?

Thank you!

Chem_Mod
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Re: F5: Problem deciding significant figures

Postby Chem_Mod » Thu Oct 05, 2017 10:57 am

The sig figs depend on the numbers you used during calculation. For some reason, the solutions manual uses 1.0079 as the molar mass of Hydrogen, which has 5 sig figs, so the final answer uses 5 sig figs. The rest of the atoms, it used 4 sig fig molar masses. In this class, you would use 1.008 as the molar mass of hydrogen, so all the answers would have 4 sig figs in this problem.

Elizabeth Bamishaye 2I
Posts: 54
Joined: Fri Sep 29, 2017 7:04 am

Re: F5: Problem deciding significant figures

Postby Elizabeth Bamishaye 2I » Thu Oct 05, 2017 12:39 pm

I used four sig figs for the whole problem. I generally always use 1.008 as the molar mass of hydrogen so I did not have this problem. It would also help if you calculated it all and rounded the hydrogen to thousandths if you used 1.0078 as the molar mass of hydrogen so you would get 100% at once instead of 99.9997%.


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