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If there is a possibility to be more accurate, honestly just take the extra time to do it because sometimes rounding can lead to drastic differences in the answer because of the small amount of substances in some problems.
when determining molar mass and using it to derive another unit, I personally don't round the molar mass unless it has 2 decimal points with 9's (2.99 up to 3) this way, the answer I get in the end is most accurate and allows me to round up to the correct number of sig figs and a more accurate value
On the textbook problems I rounded up to 16 and the significant figures after the decimal point were off from the textbook answer that used 15.999, but it still said that I got it correct. I don't think that it should matter to much. I still recommend talking to your TA to see what they say though.
mayarivers3I wrote:When using the atomic weight to calculate molar mass, does it matter if we round the atomic weight. For instance, would there be a difference in my answer if I used 15.999 or 16 for oxygen?
I think it depends on the number of sigfigs you need to use. 16 often works when I'm doing the HW problems, unless you are using more than 6 sig figs or want to be very precise with your answer. Hope this helps!
16 should be fine (I have also been rounding when the molar mass is super close to the next nearest whole number), but if you take into account sig figs, the general rule is to take 4 decimal places of a molar mass.
I honestly think it really doesn’t make too much of a difference. I personally use 15.999g just to be safe. However, since the difference between the numbers are extremely small. I doubt it would cause your answer to be significantly off if you used 16g instead of 15.999g.
As a whole, once that number is plugged into different equations, it won't matter too much whether you used 15.999 or 16.000 because of the minute difference but I would use exactly the number seen on the periodic table that he provided. I think if the answer asks for a lot of significant figures, also, that 15.999 should especially be used to account for accuracy.
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