## Empirical Formulas Rounding and Multiplying

Amy Xiao 1I
Posts: 101
Joined: Sat Jul 20, 2019 12:15 am

### Empirical Formulas Rounding and Multiplying

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?

105335337
Posts: 103
Joined: Sat Aug 24, 2019 12:15 am

### Re: Empirical Formulas Rounding and Multiplying

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.

Posts: 87
Joined: Sat Aug 24, 2019 12:15 am

### Re: Empirical Formulas Rounding and Multiplying

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!

Luyan Zhang - 2D
Posts: 103
Joined: Sat Jul 20, 2019 12:16 am

### Re: Empirical Formulas Rounding and Multiplying

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?

Alan Wu
Posts: 61
Joined: Sat Sep 14, 2019 12:16 am

### Re: Empirical Formulas Rounding and Multiplying

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.

Amy Xiao 1I
Posts: 101
Joined: Sat Jul 20, 2019 12:15 am

### Re: Empirical Formulas Rounding and Multiplying

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.

Posts: 58
Joined: Thu Jul 25, 2019 12:15 am

### Re: Empirical Formulas Rounding and Multiplying

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.

KBELTRAMI_1E
Posts: 108
Joined: Sat Jul 20, 2019 12:17 am

### Re: Empirical Formulas Rounding and Multiplying

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!

KBELTRAMI_1E
Posts: 108
Joined: Sat Jul 20, 2019 12:17 am

### Re: Empirical Formulas Rounding and Multiplying

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?

Amy Xiao 1I
Posts: 101
Joined: Sat Jul 20, 2019 12:15 am

### Re: Empirical Formulas Rounding and Multiplying

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.

ATingin_3I
Posts: 51
Joined: Fri Aug 30, 2019 12:17 am

### Re: Empirical Formulas Rounding and Multiplying

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?

Esha Chawla 2E
Posts: 108
Joined: Thu Jul 25, 2019 12:17 am

### Re: Empirical Formulas Rounding and Multiplying

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.