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Empirical Formulas Rounding and Multiplying

Posted: Sat Sep 28, 2019 2:26 pm
by Amy Xiao 1I
What should the threshold be for decimals when solving for empirical formulas? I think that if the results are 0.1 away from the nearest whole number, then you round to that whole number. Otherwise, I think you multiply to the nearest whole number. However, I see in some example problems, like one we did in discussion, where the decimal was 2.26 and it was still rounded down to 2. What should be the general rule of thumb for these numbers?

Re: Empirical Formulas Rounding and Multiplying

Posted: Sat Sep 28, 2019 2:54 pm
by 105335337
I personally feel like the general rule of thumb for round should include only integers ending in 0.5 or 0.33. Anything else, can either be rounded up or down.
For example: If your result is a number that is 2.55, obviously round that to just 2.5.

Re: Empirical Formulas Rounding and Multiplying

Posted: Sat Sep 28, 2019 3:38 pm
by Mashkinadze_1D
I agree with the other user that the amounts should be leaning towards a value usch as 0.5 or 0.33. In addition, I would like to add that each step of the way to use the correct sig figs because this personally has helped me to find values that I can see where to round to more so. In many situations I feel that manipulation of numbers by us also is causing some of the issues. Hope this also helps!

Re: Empirical Formulas Rounding and Multiplying

Posted: Sat Sep 28, 2019 4:00 pm
by Luyan Zhang - 2D
Amy Xiao 1H wrote:What should the threshold be for decimals when solving for empirical formulas? I think that if the results are 0.1 away from the nearest whole number, then you round to that whole number. Otherwise, I think you multiply to the nearest whole number. However, I see in some example problems, like one we did in discussion, where the decimal was 2.26 and it was still rounded down to 2. What should be the general rule of thumb for these numbers?


What was the problem you did in discussion? Do you have a picture of it?

Re: Empirical Formulas Rounding and Multiplying

Posted: Sat Sep 28, 2019 4:29 pm
by Alan Wu
Another thing you should remember to do is to not round intermediate answers to the desired sig figs. Directly take whatever number you got from your calculator and copy it onto the next line to perform the calculation. Many often round the intermediate answers and that could result in undesirable final results.

Re: Empirical Formulas Rounding and Multiplying

Posted: Sat Sep 28, 2019 5:23 pm
by Amy Xiao 1I
905312474 - 1L wrote:
Amy Xiao 1H wrote:What should the threshold be for decimals when solving for empirical formulas? I think that if the results are 0.1 away from the nearest whole number, then you round to that whole number. Otherwise, I think you multiply to the nearest whole number. However, I see in some example problems, like one we did in discussion, where the decimal was 2.26 and it was still rounded down to 2. What should be the general rule of thumb for these numbers?


What was the problem you did in discussion? Do you have a picture of it?


It was about Diazepam with mass composition 68.49% C, 4.60% H, 12.45% Cl, 9.84% N, 5.62% O. What is the empirical formula? For example the lowest moles gotten were 0.3512 mol of O and Cl. If you divide the moles of C (5.703) by the 0.3512, you would get 16.238. In our discussion we rounded this to 16.

Re: Empirical Formulas Rounding and Multiplying

Posted: Sat Sep 28, 2019 7:57 pm
by Adelpha Chan 1B
If the decimal is 2.26, I think you would have to multiply all the numbers you have already retrieved by 4. This would make 2.26 much closer to a whole number and avoid rounding numbers far from a whole number. This would be similar to the logic that follows how numbers ending in 0.5 and 0.33 are ultimately expressed in an empirical formula.

Re: Empirical Formulas Rounding and Multiplying

Posted: Sun Sep 29, 2019 3:55 pm
by KBELTRAMI_1E
Mashkinadze_1D wrote:I agree with the other user that the amounts should be leaning towards a value usch as 0.5 or 0.33. In addition, I would like to add that each step of the way to use the correct sig figs because this personally has helped me to find values that I can see where to round to more so. In many situations I feel that manipulation of numbers by us also is causing some of the issues. Hope this also helps!


This is very helpful!

Re: Empirical Formulas Rounding and Multiplying

Posted: Sun Sep 29, 2019 3:56 pm
by KBELTRAMI_1E
105335337 wrote:I personally feel like the general rule of thumb for round should include only integers ending in 0.5 or 0.33. Anything else, can either be rounded up or down.
For example: If your result is a number that is 2.55, obviously round that to just 2.5.


For the sake of multiplication right?

Re: Empirical Formulas Rounding and Multiplying

Posted: Sun Sep 29, 2019 10:15 pm
by Amy Xiao 1I
105335337 wrote:I personally feel like the general rule of thumb for round should include only integers ending in 0.5 or 0.33. Anything else, can either be rounded up or down.
For example: If your result is a number that is 2.55, obviously round that to just 2.5.


I understand that you would round 2.55 to 2.5, but 2.5 is not a number that you can use in an empirical formula. Would you then have to multiply the 2.5 by 2 to get 5, which is an integer? It feels to me like if you do that, you might get inaccurate results.

Re: Empirical Formulas Rounding and Multiplying

Posted: Mon Sep 30, 2019 1:33 pm
by ATingin_3I
Mashkinadze_1D wrote:I agree with the other user that the amounts should be leaning towards a value usch as 0.5 or 0.33. In addition, I would like to add that each step of the way to use the correct sig figs because this personally has helped me to find values that I can see where to round to more so. In many situations I feel that manipulation of numbers by us also is causing some of the issues. Hope this also helps!


Should we always use the correct number of sig figs for each step or should we keep the more exact numbers in our interim steps and then apply sig figs rules at the end to get the most accurate number we can?

Re: Empirical Formulas Rounding and Multiplying

Posted: Mon Sep 30, 2019 2:01 pm
by Esha Chawla 2E
So far, the way I've been doing it is by correct number of significant figures at the very end of the problem. I believe the textbook also does this, but we should check in with Professor Lavelle just to make sure.