Question

How many chlorine atoms are contained in a `2*mol` quantity of `FeCl_3`?

Answer 1

`3.6*10^24` Chlorine atoms.

Explanation:

Each `FeCl_3` has three Chlorines.
Here, we can use a conversion factor.
`(3Cl`/molecule)`*(6.022*10^23` molecules`/mol)*(2.0mol)`
Molecules and molecules cancel out. Moles and moles cancel out.
We are left with:
`3Cl*6.022*10^23*2.0`
Simplifying and giving the answer to 2 significant figures, we get:
`3.6*10^24` Chlorine atoms.

Answer 2

`6xxN_A` chlorine atoms, where `N_A=6.022xx10^23`

Explanation:

If you were asked how many chlorine atoms there were in `"1 dozen"` `FeCl_3` formula units, I think you would very quickly answer that there were `"3 dozen"`, i.e. `36` chlorine atoms.

Here you were asked the SAME QUESTION using the mole, `N_A=6.022xx10^23*mol^-1` as your counting unit.

And thus there are ................

`2*molxx3*"chlorine atoms/formula unit"xx6.022xx10^23*mol^-1`

`=??*"chlorine atoms"`.