Sig figs and molar mass

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haley f
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Sig figs and molar mass

Postby haley f » Thu Oct 08, 2020 3:11 pm

When taking the molar masses off the periodic table, how many decimal points do we need to use? Is it generally okay to use 1 for Hydrogen and 12 for Carbon?

Lauren Mungo 1K
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Re: Sig figs and molar mass

Postby Lauren Mungo 1K » Thu Oct 08, 2020 3:31 pm

Hi! From what I have heard, you should use the amount of decimals given on the periodic table (there is one on the class website) and then round to significant figures at the end of the problem in order to give a more accurate answer.

Claire_Latendresse_1E
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Re: Sig figs and molar mass

Postby Claire_Latendresse_1E » Thu Oct 08, 2020 3:33 pm

Hi! I tend to use all of the figures listed on the periodic table for my calculations so that my answer is more accurate, and then I round to the least number of sig. figs. given in the problem (if one of the numbers given only has two figures, I'll round my final answer to two figures as well).

Ryan Laureano 3I
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Re: Sig figs and molar mass

Postby Ryan Laureano 3I » Thu Oct 08, 2020 3:34 pm

As a general rule for chemistry, whenever there are decimals, it is better to stay true to the original number. For example, hydrogen has a molar mass of 1.008 g/mol (1.00784 g/mol to be exact) and using 1 g/mol instead can have drastic effects in your calculations. I like to keep the number I see on the periodic table and then round to the appropriate sig figs after the calculation.

Anya Holbrook 1E
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Re: Sig figs and molar mass

Postby Anya Holbrook 1E » Thu Oct 08, 2020 3:36 pm

Hi! I find that it's usually best to use what's given on the periodic table (I've heard from others that we'll be given one for exams?). Usually most periodic tables you find just by looking online have three decimal places but I've found that rounding to two doesn't make that much of a different in the calculations!

Katie Lam 2J
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Re: Sig figs and molar mass

Postby Katie Lam 2J » Thu Oct 08, 2020 4:55 pm

Hi! The periodic table I use has 4 digits after the decimal point. What I do is I use the entire number in my calculations. I try not to round while I am working through the problem. I usually keep 4 digits after the decimal point for every value in my calculation. Only at the end do I round my number to the least amount of sig figs given in the values in the question. Hope this helps :)

Rylee Mangan 1K
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Re: Sig figs and molar mass

Postby Rylee Mangan 1K » Thu Oct 08, 2020 5:00 pm

For the most accuracy, use whatever numbers are given on the provided periodic table. For example, Sapling provides its own periodic table so when completing the homework I would refer to that table only. And we are all given the same table for exams. Hope that helps!

Earl Garrovillo 2L
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Re: Sig figs and molar mass

Postby Earl Garrovillo 2L » Thu Oct 08, 2020 5:04 pm

Like everyone else said, it's typically best to use the listed molar mass on the periodic table. Second best option would probably be to round to at least 3 decimals. It's always best to get the most accurate answer we can (but if you are in a timecrunch, rounding elements like hydrogen, carbon, and oxygen to the nearest whole number likely won't affect your answer too much).

Brandon Gruender 3F
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Re: Sig figs and molar mass

Postby Brandon Gruender 3F » Thu Oct 08, 2020 5:06 pm

What I do is I use the periodic table given by Sapling, and use the correct amount of significant figures given by the problem(always use the least amount of sig figs presented by a piece of the equation). We all use the same periodic table during tests, but generally I would use Sapling as the periodic table on there is a great resource.

Lily Anne Garcia 1C
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Re: Sig figs and molar mass

Postby Lily Anne Garcia 1C » Thu Oct 08, 2020 5:07 pm

I usually use the entire value that's given on the periodic table. This is so that I can get a more accurate answer, avoiding round-off error. Once your final value is calculated you can adjust the answer to the amount of sig figs for that specific problem.

Namratha Gujje
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Re: Sig figs and molar mass

Postby Namratha Gujje » Thu Oct 08, 2020 5:13 pm

Hi! I usually use the exact value given on the periodic table. For the homework I tend to use the one on sapling so I can use values that they have. However, at the end of the problem I would round the answer to the lowest amount of sig figs in the problem.

Lung Sheng Liang 3J
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Re: Sig figs and molar mass

Postby Lung Sheng Liang 3J » Thu Oct 08, 2020 5:26 pm

Hi, it is usually ideal to use the exact value the periodic table gives you when performing calculations. However, if you do decide to round it to however many sig figs, you should keep it consistent by rounding each value to the same number of sig figs.

Talia Dini - 3I
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Re: Sig figs and molar mass

Postby Talia Dini - 3I » Thu Oct 08, 2020 5:39 pm

Hi!! I have been taught to use the exact values on the periodic table when calculating molar mass. Once I have done all of the calculations, I round my final answer to the number of significant figures that are necessary. This is important to practice because it will help you get the most accurate answer at the end!

Christine Nguyen 3D
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Re: Sig figs and molar mass

Postby Christine Nguyen 3D » Thu Oct 08, 2020 5:40 pm

Like mostly everyone else, I use all the numbers given to me for my calculations to be as accurate as possible and write my final answer according to how many sig figs the problem indicated.

Sophia Kalanski 1A
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Re: Sig figs and molar mass

Postby Sophia Kalanski 1A » Fri Oct 09, 2020 12:03 am

I think its best to use the exact value as given to you on the periodic table to get the most accurate molar mass and then you should round it to how ever many sig figs necessary or as indicated in the end. You want to still make sure that your answer is as accurate as possible.

Megan Lu 3D
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Re: Sig figs and molar mass

Postby Megan Lu 3D » Fri Oct 09, 2020 12:15 am

Hi! Like others, I’ve been using as many decimal points as detailed in the period table posted on the class website. I assume that that is the periodic table we use for this class, so I stick to those values.

Sejal Parsi 3K
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Re: Sig figs and molar mass

Postby Sejal Parsi 3K » Fri Oct 09, 2020 2:18 am

Hi, as said by everyone above, it is best to use as many sig figs as given on the periodic table, and then to round your final answer appropriately to the sig figs given within the problem.

Lillian
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Re: Sig figs and molar mass

Postby Lillian » Fri Oct 09, 2020 9:54 am

I don't think Lavelle will mind either way, especially since all the interactions and quizzes/tests are multiple choice. But like many others have said, using the most sig figs as possible until you have the final answer is best :)

George Hernandez 3I
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Re: Sig figs and molar mass

Postby George Hernandez 3I » Fri Oct 09, 2020 10:10 am

I find, especially when I'm trying to figure out the empirical formula, that using the entire value makes finding the approximate mole ratio a lot easier. For instance, I was in my discussion earlier and I found that if I used the entire mass without rounding, the mole ratio for the elements in the compound came out to be about 1:5.9, which I can then assume it being 1:6. If I started rounding from the very beginning, my mole ratio would be 1:5.5, which makes it very uncertain whether the ratio should be 1:5 or 1:6. So yes, I generally use the entire value whenever possible :)


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