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When finding empirical formula/molecular formula or in general for chemistry, does it matter whether we use 15.99 grams/mole or 16.00 grams/mole for the mass of oxygen? I tried doing the same calculations with both numbers and I get a slightly different answer each time. The result is not off by much, but I would like to know which one is preferable so I do not happen to miscalculate anything for future exams.
I believe that using 16 grams/mole for the mass of oxygen should be okay as Dr. Lavelle has done this in his example problems for the Audio-Visual Focus Topics as well as during lectures. I feel that using this shouldn’t affect your answer by much and should still allow you to receive full credit but I am not completely sure.
I remembered from class that it's better to aim for 3 digits after the decimal point (for significant figures), and it's definitely more precise to use 15.99 g/mol for oxygen. I don't think points will be taken off for this during exams, but I'm not totally certain about how much you can round up.
Hope this helps! :)
Hope this helps! :)
Last edited by octaviahuang1f on Fri Apr 06, 2018 1:24 pm, edited 1 time in total.
That doesn't make a big difference. Since these calculations are not being used for lab procedures, it is not important to be 100% precise. When you find the empirical formula, you round ratios as well. For example 5.12 moles of C can just be denoted 5 C in the empirical formula. Therefore, it is ok to use 16 g/mol for the mass of oxygen. Just remember, however, that the mass for one ATOM of oxygen is approximately 16 g/mol but the mass of a MOLECULE of oxygen (as in oxygen gas) is twice that of the atom, so 32 g/mol. Hope this helped! :)
I'm sure you can use 16 grams/mol since Dr. Lavelle has used that in lectures. There's not much difference between 15.99 grams/mol and 16 grams/mol so I would go for the 16 since I'm sure rounding is preferred.
There are no differences, really. There are many versions of the periodic table; however, it is best to just follow the periodic table in our book, which is 16.00 g/mol, and Professor Lavelle uses that as well. Besides, after we take significant figures into account, the answer will most likely be the same whether you used 15.99 or 16.00.
The safest thing to do in an exam is to use the value in the periodic table that is provided for you.
That being said, will utilizing 15.99 grams/mole or 16 grams/mole entail that the TA(s) or test grader understands the differences in sig figs the end answer will hold because of these varying numbers/computations?
It really does not matter much for most of the problems we do in this class. It will matter for cases in which we are working with sensitive analysis where numbers are maybe (10+ sig figs) and such differences will start to matter in reaching your conclusions.
Good practice would be to use 15.999. But in exam conditions, when you might not have enough time to type in a lot of decimal places/digits, I asked my TA and she mentioned that she would not deduct points as long as your working out is correct and showed and also as long as the final answer is very close to the right answer. For example, if the actual answer was 0.998, and you wrote 1.000, then she said she would still accept it.
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