Sig Figs for elements on Periodic table

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Jason_Glass_2L
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Sig Figs for elements on Periodic table

Postby Jason_Glass_2L » Mon Oct 05, 2020 1:23 pm

Quick Question: Since some periodic tables only go to 4 sig figs and some go to 5 sig figs, which one should we use for the class? I ask this because I feel like if I use a table with a 4 sig figs I might get an answer off by like 0.01 which would be marked as wrong.

Anil Chaganti 3L
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Re: Sig Figs for elements on Periodic table

Postby Anil Chaganti 3L » Mon Oct 05, 2020 1:25 pm

Hi, I always tend to use 4 sig figs and I haven't been off many times. I think you should be fine if you are off by 0.01. I would stick with four for now as most periodic tables I've seen use 4 sig figs.

Ke Huang 2G
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Re: Sig Figs for elements on Periodic table

Postby Ke Huang 2G » Mon Oct 05, 2020 1:31 pm

I think we should probably go with four sig figs since the periodic table on the resources part of the website has four.

Laura 3l
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Re: Sig Figs for elements on Periodic table

Postby Laura 3l » Mon Oct 05, 2020 1:35 pm

Yes, I agree that four significant figures should be fine.

Adrienne Yuh 2B
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Re: Sig Figs for elements on Periodic table

Postby Adrienne Yuh 2B » Mon Oct 05, 2020 2:41 pm

I would go with 4 sig figs! I think in most chemistry problems, if your answer is accurate within the range of +/- %5 it's fine? That's what my teacher in high school went by!

Audrey Han 3L
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Re: Sig Figs for elements on Periodic table

Postby Audrey Han 3L » Mon Oct 05, 2020 3:00 pm

In general 4 should be good! Personally, I only use more if I'm trying to solve for something like empirical/molecular formula just so I don't get numbers that I can't really convert to whole numbers (even then this might be extra though).

Sahaj Patel Lec3DisK
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Re: Sig Figs for elements on Periodic table

Postby Sahaj Patel Lec3DisK » Mon Oct 05, 2020 3:06 pm

Generally when looking at the Sig Figs for an element on the Periodic Table of Elements, it will depend on the question. If the question has numbers with 4 sig figs in it, for example, then you would use 4 sig figs for the elements that are used in the problem. You can always wait until the end to round out your sig figs anyways if you do not want to round to the appropriate number of sig figs immediately. But just keep in mind it usually depends on the problem there isn't a flat out rule for sig figs it usually depends on the sig figs portrayed in the problem.

Gabriel Nitro 1E
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Re: Sig Figs for elements on Periodic table

Postby Gabriel Nitro 1E » Mon Oct 05, 2020 3:13 pm

Hi,

I agree. Typically, with the periodic table when doing calculations (i.e. stoichiometry, empirical formulas, molecular formulas) I would use the periodic table with 4 significant figures. On the one hand it offers an apt number when dealing with numerical calculations, such as the ease with mistakes when calculating, and in terms of convenience a +/- 0.01 difference should be fine.

JaesalSoma1E
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Re: Sig Figs for elements on Periodic table

Postby JaesalSoma1E » Mon Oct 05, 2020 3:18 pm

I'm pretty sure it would not matter how many sig figs are on the periodic table because those values are known. Instead you would determine the number of sig figs from any given or measured values in the problem. For example, if it said 1.53 mol of CO2, then you would use 3 sig figs throughout the problem, but when calculating the molar mass of CO2 you can use whatever the value is on the periodic table without correcting for sig figs.

Jordan Tatang 3L
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Re: Sig Figs for elements on Periodic table

Postby Jordan Tatang 3L » Mon Oct 05, 2020 4:34 pm

For me, when the question uses common elements such as oxygen, carbon, or hydrogen I use 16,12.01, and 1.008 (g.mol^-1) respectively, but if the question uses elements that I have to look up on the periodic table I just use the exact values and round to the correct sig-figs at the end. Hopefully that helps!

Sreeram Kurada 3H
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Re: Sig Figs for elements on Periodic table

Postby Sreeram Kurada 3H » Mon Oct 05, 2020 4:45 pm

A good rule of thumb is to use 4 sig figures unless the question states otherwise. Hope this helps :)

Haochen He 3L
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Re: Sig Figs for elements on Periodic table

Postby Haochen He 3L » Mon Oct 05, 2020 8:58 pm

Hi!! I usually use 4 sig figs. It seems to be enough based on the questions I've solved.

Katie Nye 2F
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Re: Sig Figs for elements on Periodic table

Postby Katie Nye 2F » Mon Oct 05, 2020 9:09 pm

Personally, I use four sig figs from the masses on periodic table and then adjust the final answer after every calculation is complete to get the most accurate and precise answer possible.

Megan Singer 3D
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Re: Sig Figs for elements on Periodic table

Postby Megan Singer 3D » Mon Oct 05, 2020 9:11 pm

JaesalSoma1E wrote:I'm pretty sure it would not matter how many sig figs are on the periodic table because those values are known. Instead you would determine the number of sig figs from any given or measured values in the problem. For example, if it said 1.53 mol of CO2, then you would use 3 sig figs throughout the problem, but when calculating the molar mass of CO2 you can use whatever the value is on the periodic table without correcting for sig figs.


I'd have to disagree with you there Jaesal. Although those values are known, they are not exact. For example, the atomic mass of carbon is written as 12.01 u on most tables, but if you look up the molar mass of carbon online, you'll find that a more exact value is 12.0107 u. Therefore, if you use the 4 sig fig value typically given on a table, you wouldn't be able to determine the answer to your problem to any more than 4 sig figs without being slightly inaccurate. (your example works here because the given values you used in your problem were less than 4 sig figs). I think in general though, the number of sig figs tends to be determined by the values given in the problem not the molar masses, because values aren't typically given with more than 4 sig figs.

Megan Singer 3D
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Re: Sig Figs for elements on Periodic table

Postby Megan Singer 3D » Mon Oct 05, 2020 9:16 pm

Sorry for the extra post, but I'd just like to re-emphasize for Jason that as long as your final answer is 4 sig figs or less , you won't be off at all. If your final answer is 5 sig figs, you'd have to use a molar mass accurate to 5 sig figs to get a fully accurate answer.


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