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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?
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!
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.
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.
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.
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.
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.
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.
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.
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).
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.
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.
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