Sig Figs Throughout Problems

Moderators: Chem_Mod, Chem_Admin

Joshua Baysa 1J
Posts: 10
Joined: Wed Sep 21, 2016 2:59 pm

Sig Figs Throughout Problems

Postby Joshua Baysa 1J » Tue Sep 27, 2016 10:14 am

The use of Sig Figs used to be handled differently between both my Honors Chemistry and AP Chemistry teachers during High School and I just want to make things clear. Do we consider Sig Figs only on the final answer or for each calculation done for the problem?

Prat3010
Posts: 11
Joined: Wed Sep 21, 2016 2:56 pm

Re: Sig Figs Throughout Problems

Postby Prat3010 » Tue Sep 27, 2016 10:28 am

I had the same question as well! I'm not sure how much this will help, but in my high school we always used the actual values throughout the problem and rounded it off only in the end. You should get the most accurate answer that way!

Alex Chen 1B
Posts: 24
Joined: Wed Sep 21, 2016 2:57 pm
Been upvoted: 1 time

Re: Sig Figs Throughout Problems

Postby Alex Chen 1B » Tue Sep 27, 2016 10:30 am

You shouldn't round during the problem, but you should definitely keep track of the sig figs on each calculation that you make as you progress through the problem. And once you reach your final answer, figure out how many sig figs there are based on the sig figs of your previous calculations. One method that my AP Chemistry teacher taught me is that for every calculation that you make, you should underline the place where the sig fig goes to. So for example, if 3.45621 has three sig figs, you would underline the number 5. This way you can keep track of how many sig figs are in your problem and make it easier for you to determine the sig figs of your final answer.

Amy Ko 3C
Posts: 24
Joined: Sat Jul 09, 2016 3:00 am

Re: Sig Figs Throughout Problems

Postby Amy Ko 3C » Tue Sep 27, 2016 10:38 am

Other than using sig figs of the previous calculation, another useful method to determine the number of sig figs that the final answer should have is by looking at the sig figs of the provided numbers in the original problem. But overall, according to my AP chemistry teacher, you should definitely keep track of sig figs while you go through individual calculations.

Kaitlin_Reeves_1C
Posts: 22
Joined: Wed Sep 21, 2016 2:59 pm

Re: Sig Figs Throughout Problems

Postby Kaitlin_Reeves_1C » Tue Sep 27, 2016 10:44 am

Is there a standard number of sig figs we are supposed to have for certain kinds of problems? Or does the number of sig figs in an answer vary with each individual problem?

Amy Ko 3C
Posts: 24
Joined: Sat Jul 09, 2016 3:00 am

Re: Sig Figs Throughout Problems

Postby Amy Ko 3C » Tue Sep 27, 2016 10:51 am

Number of sig figs vary with problems. For example, a dilution problem may ask you to dilute 5.00 mL of some 1.0M solution to 1.00 mL of unknown concentration. In this case, you use M1V1=M2V2 and multiplication in sig fig rule states to use least number of sig fig. Therefore, you will have 2 sig fig in the final answer. Another example may be to calculate the number of moles in 4.233 grams of glucose given the molar mass. The problem is given with a 4 sig fig number, thus your answer should contain 4 sig figs.

Kiana_Shibata_2G
Posts: 24
Joined: Wed Sep 21, 2016 2:56 pm

Re: Sig Figs Throughout Problems

Postby Kiana_Shibata_2G » Tue Sep 27, 2016 5:10 pm

Yeah, I would say always round to the correct number of sig figs at the end. If you round for every single calculation, you will end up with a number that could be very far from the correct answer because of rounding errors at every calculation. It also makes your answer more accurate, I think.

Logan 3C
Posts: 22
Joined: Wed Sep 21, 2016 2:57 pm

Re: Sig Figs Throughout Problems

Postby Logan 3C » Tue Sep 27, 2016 8:21 pm

My TA told us today that it is best if you use the entire number through the problem and wait to round sig figs until the very end. This gives yo the most accurate answer. So as long as you remember to round and add units at the end of the problem, you should be good.

edhuang
Posts: 24
Joined: Wed Sep 21, 2016 2:58 pm

Re: Sig Figs Throughout Problems

Postby edhuang » Tue Sep 27, 2016 8:50 pm

So in high school chemistry (regular and AP) I was used to using molar masses down to the hundredths, because that was the periodic table I was given. I was wondering if I could still round to the hundredths for molar masses in this class, though the periodic table rounds to the thousandths and sometimes ten thousandths. It just seems rather unnecessary and tedious to have to use molar masses to the ten thousandths.

Brianna Wummer 2L
Posts: 19
Joined: Wed Sep 21, 2016 2:56 pm

Re: Sig Figs Throughout Problems

Postby Brianna Wummer 2L » Tue Sep 27, 2016 9:12 pm

I would use the values given on the periodic table that we were provided or the values given in the problem, even if there are more decimal places than you are used to. My TA also said that its better to use the whole number given and only round to the correct sig figs at the end, as it provides the most accurate answer.

alvitaxiao
Posts: 18
Joined: Sat Jul 09, 2016 3:00 am

Re: Sig Figs Throughout Problems

Postby alvitaxiao » Tue Sep 27, 2016 10:10 pm

The TA today said that when doing problems such as limiting reactants, you follow the sig figs based on the number you used to get the final answer. For example, if you were finding the amount of X formed from Y + Z -> X and you were given 10 g of Y and 10.00 g of Z and Z was the limiting reactant, then the final answer of X formed would be 4 sig figs since you used the number "10.00 g" as opposed to 1 sig fig (from the 10 g given in the problem).

Myra_Zhan_2N
Posts: 25
Joined: Fri Jul 22, 2016 3:00 am

Re: Sig Figs Throughout Problems

Postby Myra_Zhan_2N » Wed Sep 28, 2016 12:37 am

My TA said to keep the numbers as you work through the problem and find the final answer according to sigfigs at the end. He also mentioned a way to keep track of the final number of sigfigs is to underline the supposed final number of sigfigs each time as you work through each step of the problem.

Zsanielle Moncayo 1E
Posts: 13
Joined: Wed Nov 18, 2015 3:00 am
Been upvoted: 1 time

Re: Sig Figs Throughout Problems

Postby Zsanielle Moncayo 1E » Wed Sep 28, 2016 6:45 pm

Based on previous experiences with Chem classes I've found it easier to keep all values kept to the amount of sig. figs asked in the questions and not round up. Once at the final answer you do the same and leave answer with the amount of sig. figs asked. Basically try not to round so you can keep the value more accurate for your final answer.


Return to “Significant Figures”

Who is online

Users browsing this forum: No registered users and 2 guests