Significant Figures Using the Periodic Table

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Ethan Goode 2H
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Significant Figures Using the Periodic Table

Postby Ethan Goode 2H » Wed Oct 07, 2020 2:08 pm

How many decimals of the molar masses of each element should we use from the periodic table when calculating overall molar masses of a compound?

Chem_Mod
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Re: Significant Figures Using the Periodic Table

Postby Chem_Mod » Wed Oct 07, 2020 2:09 pm

It's best to get in the habit of using all the decimal places of the atomic masses that you're dealing with so that your answer is more accurate.

Kailani_Dial_2K
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Re: Significant Figures Using the Periodic Table

Postby Kailani_Dial_2K » Wed Oct 07, 2020 3:50 pm

It will be more clear on exams because everyone will be given the same periodic table with the same numbers. I ordered the periodic table handout that was recommended by the professor which has each of the molar masses rounded to the second decimal point. Using this periodic table I have been able to get the correct calculations. With that being said I would say to use it to at least the second decimal point.

Cooper Kinne 2E
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Re: Significant Figures Using the Periodic Table

Postby Cooper Kinne 2E » Wed Oct 07, 2020 3:53 pm

Does anyone have a link for the recommended periodic table mentioned?

Adalia 3E
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Re: Significant Figures Using the Periodic Table

Postby Adalia 3E » Wed Oct 07, 2020 3:54 pm

I would recommend using more decimal places than the sig figs the question asks for (i.e. if the question provides 0.500, you should probably use 4 or more sig figs) and then round to the correct number of sig figs at the end of the problem

Adalia 3E
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Re: Significant Figures Using the Periodic Table

Postby Adalia 3E » Wed Oct 07, 2020 4:22 pm

Cooper Kinne 3E wrote:Does anyone have a link for the recommended periodic table mentioned?

https://courses.vitalsource.com/ This link has a place to purchase a periodic table, but there is also a free periodic table PDF on his site that you can just ctrl+f "periodic table" for
Edit: Oops, the link I sent can only be accessed through CCLE in the "UCLA Store course material" tab

Anya Holbrook 1E
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Re: Significant Figures Using the Periodic Table

Postby Anya Holbrook 1E » Wed Oct 07, 2020 4:25 pm

I think most periodic tables you find on the internet will show three decimal places, but I've found that rounding to two decimal places doesn't change much in the grand scheme of things. All in all, I think it'll ultimately depend on what Dr. Lavelle says he wants on exams!

Jaden Ji 2K
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Re: Significant Figures Using the Periodic Table

Postby Jaden Ji 2K » Wed Oct 07, 2020 4:28 pm

Here's the link to the textbook's periodic table!
https://www.saplinglearning.com/ibiscms ... d=13094939
I've been using this one and I've gotten answers right using all the decimal places and correct sig figs with this.

Michelle Nguyen 3F
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Re: Significant Figures Using the Periodic Table

Postby Michelle Nguyen 3F » Thu Oct 08, 2020 8:37 am

For the Sapling homework online, I usually would just use the period table provided from the Sapling learning (^like the one above). For exams, we should just wait to see if the exam contains a periodic table along with the questions. Usually, the first two decimal places would be more common to see!

John_Tran_3J
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Re: Significant Figures Using the Periodic Table

Postby John_Tran_3J » Thu Oct 08, 2020 10:37 am

To receive the most accurate answer, u should apply the atomic weights as given through the periodic table (avoid using whole numbers, they can mess you up.)

Zainab Jamali 1H
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Re: Significant Figures Using the Periodic Table

Postby Zainab Jamali 1H » Thu Oct 08, 2020 10:56 am

I was wondering the same thing, thank you for starting this thread! Personally, I have always just rounded to three digits but the information in this thread is helpful!

Zainab Jamali 1H
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Re: Significant Figures Using the Periodic Table

Postby Zainab Jamali 1H » Thu Oct 08, 2020 10:57 am

Jaden Ji 3K wrote:Here's the link to the textbook's periodic table!
https://www.saplinglearning.com/ibiscms ... d=13094939
I've been using this one and I've gotten answers right using all the decimal places and correct sig figs with this.


This is a great resource, thank you!

Jasmine Yi 1G
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Re: Significant Figures Using the Periodic Table

Postby Jasmine Yi 1G » Thu Oct 08, 2020 11:37 am

I don't think anyone mentioned it here, but the professor has a periodic table on his website. It's free, and since it's on his website, I'm pretty sure that he would accept answers that use the values from that periodic table. In general, I wouldn't round values for molar mass because it could lead to inaccurate answers.

Melanie Lin 3E
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Re: Significant Figures Using the Periodic Table

Postby Melanie Lin 3E » Thu Oct 08, 2020 5:55 pm

Cooper Kinne 3E wrote:Does anyone have a link for the recommended periodic table mentioned?

On Lavelle's Chem 14A site, he linked pdfs of a periodic table and constants so it might be better to base your numbers off that. Otherwise, most periodic tables vary between 3 to 4 decimal places, which I don't think will make a particularly big difference in your calculations (to the point of changing your answer).


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