Total Mass

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Hannah Morales 1D
Posts: 31
Joined: Fri Sep 29, 2017 7:06 am

Total Mass

Postby Hannah Morales 1D » Fri Oct 05, 2018 4:36 pm

For a problem, I was asked what fraction was the total mass due to oxygen?

The solution manual said that you were supposed to do it a specific way but the way that I did it was as follows:


1. I got the mol of H20 and multiplied the molar mass of oxygen to get 2.67 grams of oxygen.
EX: 0.1668 mol * 16 g/mol= 2.67 g
2. Then I got the mass of oxygen, 2.67g and divided it by the total mass and got 0.3101 or 31.0% of O
EX: 2.67g/ 8.61g= .3101

In the solution mannual the answer was about .309 and they did it as another method. Would the way I did it be correct? Thanks!

emily gao 1C
Posts: 61
Joined: Fri Sep 28, 2018 12:29 am

Re: Total Mass

Postby emily gao 1C » Fri Oct 05, 2018 9:28 pm

Yes your way works: the number might not be exactly the same if you rounded each step--> general rule: keep all the sig figs until the end

Henry Krasner 1C
Posts: 64
Joined: Fri Sep 28, 2018 12:15 am

Re: Total Mass

Postby Henry Krasner 1C » Fri Oct 05, 2018 9:43 pm

Yes. As previously stated, your method does work correctly. Retaining the number of sig figs is important throughout, but you will be able to retain relatively the same answer regardless. But just to be same, check out the Sig Fig directions on the class website.

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