Posted by **Bob** on Sunday, March 8, 2009 at 9:32pm.

Calculate the total number of F (Fluorine) atoms in 12.15 mol C2HBrClF3. The answer is 2.195 x 10^25 atoms, but I am not sure how they got there. Can anyone give me a hint how to get started?

If needed (i'm not sure), the moleculatr mass of C2HBrClF3 is 197.381.

- Another Chem Problem -
**DrBob222**, Sunday, March 8, 2009 at 10:01pm
Just use dimensional analysis to see how it works. There are 6.02 x 10^23 molecules in a mole of molecules and there are 3 F atoms in the C2HBrClF3 molecule. So start with what you have and use factors to get where you want to go.

12.15 moles Cx x factor x factor = # F atoms.

12.15 moles Cx x (6.02 x 10^23 molecules Cx/1 mol Cx) x (3 F atoms/1 molecule Cx) = ??

Note that moles Cx (in the 12.15) cancel with the mol Cx in the first factor and molecules Cx in the numerator of the first factor cancel with molecules Cx in the denominator of factor 2, leaving F atoms which is the unit you want to keep.

- Another Chem Problem -
**Bob**, Sunday, March 8, 2009 at 10:16pm
Alright, now I am starting to understand. Thanks!

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