Calculating Atomic Mass of a Molecule

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Jasmine Vera 3L
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Calculating Atomic Mass of a Molecule

Postby Jasmine Vera 3L » Fri Oct 09, 2020 2:17 am

When working out Empirical and Molecular formulas, should we round the atomic mass of a molecule, and if so, which decimal place should we round to? I noticed that the decimal place that you choose does in fact have an effect on your outcome, and I am not so sure how tedious the graders will be on our exams!

Nico Medina
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Re: Calculating Atomic Mass of a Molecule

Postby Nico Medina » Fri Oct 09, 2020 4:48 am

I was wondering the same thing. Certain periodic tables show the atomic mass of elements rounded to a different decimal place, and I was wondering if there is a "standard" that we should use (i.e. hundredths, thousandths, etc.).

Peter DePaul 1E
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Re: Calculating Atomic Mass of a Molecule

Postby Peter DePaul 1E » Fri Oct 09, 2020 6:45 am

In one of the lectures Dr. Lavelle mentioned that he wants us to use the exact numbers provided on the periodic table he will provide to us (maybe it is already on the Chem 14A website). In the past my Chemistry teachers have typically said to use 4 sig figs, and then for heavier elements such as Ag (silver) to use 5 sig figs. This would mean not going past the hundreths decimal.

Can Yilgor 2D
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Re: Calculating Atomic Mass of a Molecule

Postby Can Yilgor 2D » Fri Oct 09, 2020 7:20 am

As Dr.Lavelle said in one of his lectures, a copy of the periodic table will be given each of us during assessments. Therefore, I guess we will use the values given in that particular periodic table. Also, there is a copy of IUPAC's periodic table on the CHEM 14A website if you would like to refer to while solving questions.

Jessie Hsu 1C
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Re: Calculating Atomic Mass of a Molecule

Postby Jessie Hsu 1C » Fri Oct 09, 2020 7:22 am

I agree with what others said above. The safest bet is to use 4+ sig figs as provided on Dr. Lavelle's periodic table, and never round (use values saved in your calculator) until the end.

LaurenChoi_1J
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Re: Calculating Atomic Mass of a Molecule

Postby LaurenChoi_1J » Fri Oct 09, 2020 8:02 am

i would just use whatever values are on the periodic table that Dr.Lavelle gives us and wait to round until you get to the final answer to make sure that your answer is as accurate as it can be.

Lily Carlson 1K
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Re: Calculating Atomic Mass of a Molecule

Postby Lily Carlson 1K » Fri Oct 09, 2020 8:06 am

So far using exact values on the periodic table has yielded enough accuracy. Beyond a few figures after the decimal point, the answer becomes increasingly similar regardless of how you round it. In my opinion, it's always better to be safe than sorry (a more accurate answer should be better, since sig figs don't particularly apply due to the masses of elements being given and not measured).

Inderpal Singh 2L
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Re: Calculating Atomic Mass of a Molecule

Postby Inderpal Singh 2L » Sat Oct 10, 2020 3:17 pm

I personally use the exact values provided on the periodic table and do not round until the very end of the problem. A scientific calculator should save all of your decimal points and use it later.

Carly_Lipschitz_3H
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Re: Calculating Atomic Mass of a Molecule

Postby Carly_Lipschitz_3H » Sat Oct 10, 2020 6:20 pm

Personally, I always use the exact numbers provided to me on whichever periodic table I am using, even if there are many numbers after the decimal. However, Dr. Lavelle did also say that he will provide us with a periodic table on exams, so I would suggest using the exact numbers provided on that during exams.

Lucy Weaver 1K
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Re: Calculating Atomic Mass of a Molecule

Postby Lucy Weaver 1K » Sat Oct 10, 2020 6:26 pm

I usually use the exact values provided on a periodic table, for exams I beleive we will be given a periodic table so we should just use the exact values from that and then round our answers accordingly depending on what decimal place is specified.


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