chemistry- DR BOB

and we had to round this was the question was to again
calculate the number of moles in each of the following masses
a)64.1 g of aluminum
b)28.1 g of silicon
c)0.255 g of sulfur
d)850.5 g of zinc
a) 64/27 = 2.4 mols b) 28.1g/28=1.0 mol c) 0.255/32=.0080 d)850.5/65 =13.076. I think i made some mistakes can u see if im on the right track or correct me if im wrong.. thanks in advance
also the answer has to be rounded and written in scientific notation form which ive failed and need help

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1. #1. You are in the ball park but you are allowed 3 significant figures with the 64.1 so you should have at least one more place in your answer. I used 26.98 for Al.
#2 is ok but the answer should be 1.00.
#3 should be to 3 places. I find 0.00795 (and I used 32.066 for S, not 32).
#4. I used 65.39 for Zn and obtained 13.00658 which I would round to 13.01.

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2. okay but my teacher said we were supposed to round the atomic mass.. so would that change the answer?

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