Arithmetic help in chemistry

  • Thread starter Andrew321
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  • #1
Andrew321

Main Question or Discussion Point

ok, i'm trying to get the mass of a calcium atom in kilograms...formula for converting atoms to grams is(1.00amu=1.66x10^-24g)Calcium is 40.1amu
Ok, here is the setup with it..
40.1amu/1 x 1.66x10^-24g/1.00amu x 1kg/1,000g= ...
So how am i suposed to get the answer? Could someone please put the answer our step by step for me? Thanks a bunch:smile:

Andrew
 

Answers and Replies

  • #2
ShawnD
Science Advisor
668
1
The main thing is to get the units to work out.

40.1amu * 1.66x10^-24g/amu * 1kg/1000g = 6.6566x10^-26kg

The way we did questions like this at my school was like this:
40.08g/mol * 1mol/6.02x10^23atoms * 1kg/1000g = 6.6578x10^-26kg/atom

Both ways work but I personally like the second way better. 6.02x10^23 is avogadro's number which is fairly easy to remember since you see it a lot. That 1.66x10^-24 is 1 over avogadro's number which does the same thing in both equations but it just makes it so you need to remember another number (not a good thing).
 

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