Determining Molar Mass

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mayarivers3I
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Joined: Wed Sep 18, 2019 12:18 am

Determining Molar Mass

Postby mayarivers3I » Thu Oct 03, 2019 7:26 pm

When using the atomic weight to calculate molar mass, does it matter if we round the atomic weight. For instance, would there be a difference in my answer if I used 15.999 or 16 for oxygen?

Ashley Kumar 3F
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Joined: Sat Sep 07, 2019 12:18 am

Re: Determining Molar Mass

Postby Ashley Kumar 3F » Thu Oct 03, 2019 7:32 pm

Personally, I just do 15.999 but in my discussion my TA just rounded to 16 so I think it should be fine.

Venus_Hagan 2L
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Re: Determining Molar Mass

Postby Venus_Hagan 2L » Thu Oct 03, 2019 8:02 pm

I also think the 16 would be fine. My TA also rounded during discussion.

Jacob Villar 2C
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Re: Determining Molar Mass

Postby Jacob Villar 2C » Thu Oct 03, 2019 8:05 pm

As long as the result isn't too drastically different in terms of significant figures, I would say that using 16 would be fine.

TimVintsDis4L
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Re: Determining Molar Mass

Postby TimVintsDis4L » Thu Oct 03, 2019 8:08 pm

In most cases it shouldn't matter, but if you require a certain amount of sig figs in your answer, then you would make sure that your answer isn't rounded up too much

KnarGeghamyan1B
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Re: Determining Molar Mass

Postby KnarGeghamyan1B » Thu Oct 03, 2019 11:44 pm

If there is a possibility to be more accurate, honestly just take the extra time to do it because sometimes rounding can lead to drastic differences in the answer because of the small amount of substances in some problems.

Annika Zhang 1F
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Joined: Sat Jul 20, 2019 12:15 am

Re: Determining Molar Mass

Postby Annika Zhang 1F » Thu Oct 03, 2019 11:54 pm

when determining molar mass and using it to derive another unit, I personally don't round the molar mass unless it has 2 decimal points with 9's (2.99 up to 3) this way, the answer I get in the end is most accurate and allows me to round up to the correct number of sig figs and a more accurate value

Philip
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Joined: Sat Sep 07, 2019 12:16 am

Re: Determining Molar Mass

Postby Philip » Fri Oct 04, 2019 12:01 am

It should be fine

Juliana Rosales 1H
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Joined: Wed Sep 30, 2020 9:43 pm

Re: Determining Molar Mass

Postby Juliana Rosales 1H » Mon Oct 05, 2020 3:44 pm

On the textbook problems I rounded up to 16 and the significant figures after the decimal point were off from the textbook answer that used 15.999, but it still said that I got it correct. I don't think that it should matter to much. I still recommend talking to your TA to see what they say though.

Sreeram Kurada 3H
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Re: Determining Molar Mass

Postby Sreeram Kurada 3H » Mon Oct 05, 2020 3:54 pm

If the problem specifically states specifically round to these many significant figures then you have to round, but otherwise you are fine. Hope this helps.

BKoh_2E
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Joined: Wed Sep 30, 2020 9:57 pm

Re: Determining Molar Mass

Postby BKoh_2E » Mon Oct 05, 2020 4:09 pm

In this case it shouldn't make much of a difference. Just be careful not to round too much for elements with decimals not so close to whole numbers. I personally round them to the hundredths place.

IshanModiDis2L
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Joined: Wed Sep 30, 2020 9:49 pm

Re: Determining Molar Mass

Postby IshanModiDis2L » Mon Oct 05, 2020 4:11 pm

I believe that in most cases, it shouldn't really matter. I think 16.0 would be appropriate but it would also depend on the problem. You should base it off the sig figs available in the problem.

Sid Panda 3A
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Re: Determining Molar Mass

Postby Sid Panda 3A » Mon Oct 05, 2020 4:16 pm

mayarivers3I wrote:When using the atomic weight to calculate molar mass, does it matter if we round the atomic weight. For instance, would there be a difference in my answer if I used 15.999 or 16 for oxygen?


I think it depends on the number of sigfigs you need to use. 16 often works when I'm doing the HW problems, unless you are using more than 6 sig figs or want to be very precise with your answer. Hope this helps!

Frankie Mele 3J
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Re: Determining Molar Mass

Postby Frankie Mele 3J » Mon Oct 05, 2020 4:20 pm

I think it also depends on the problem and how many sig figs are used in the variables, but I would also agree that 16.0 would be a more appropriate and safer answer than 16.

Nina Tartibi 1F
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Joined: Wed Sep 30, 2020 9:58 pm

Re: Determining Molar Mass

Postby Nina Tartibi 1F » Mon Oct 05, 2020 6:31 pm

16 should be fine (I have also been rounding when the molar mass is super close to the next nearest whole number), but if you take into account sig figs, the general rule is to take 4 decimal places of a molar mass.

Jordi M 2I
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Re: Determining Molar Mass

Postby Jordi M 2I » Mon Oct 05, 2020 6:35 pm

I always use the exact number listed on the periodic table. In the case of oxygen being 15.999 g/mol, I'm sure that rounding it up would have a negligible impact on your final answer.

Jasraj Parmar 3H
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Joined: Wed Sep 30, 2020 9:44 pm

Re: Determining Molar Mass

Postby Jasraj Parmar 3H » Mon Oct 05, 2020 6:39 pm

I honestly think it really doesn’t make too much of a difference. I personally use 15.999g just to be safe. However, since the difference between the numbers are extremely small. I doubt it would cause your answer to be significantly off if you used 16g instead of 15.999g.

Edwin Liang 1I
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Re: Determining Molar Mass

Postby Edwin Liang 1I » Mon Oct 05, 2020 7:23 pm

For rough estimates, 16 is fine, but for precise calculations, 15.999 is best.

Serena Song 1A
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Re: Determining Molar Mass

Postby Serena Song 1A » Mon Oct 05, 2020 8:22 pm

It probably wouldn't make a significant difference in most cases, but if you want to be on the safe side use 15.999.

Katie Nye 2F
Posts: 90
Joined: Wed Sep 30, 2020 9:55 pm

Re: Determining Molar Mass

Postby Katie Nye 2F » Mon Oct 05, 2020 9:12 pm

As a whole, once that number is plugged into different equations, it won't matter too much whether you used 15.999 or 16.000 because of the minute difference but I would use exactly the number seen on the periodic table that he provided. I think if the answer asks for a lot of significant figures, also, that 15.999 should especially be used to account for accuracy.


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