Question

Question #fa394

Answer 1

`"In one mole of ferric oxide?"`

Explanation:

A `"mole"` specifies a quantity of `6.022xx10^23` individual items of stuff. We use it in the same way as we would use a `"dozen"`, or a `"bakers' dozen"`, or a `"gross"`. It is simply another (admittedly large) collective number.

We have `1*mol`, `6.022xx10^23` formula units of `Fe_2O_3`, i.e. `2xxN_A` `"iron atoms"`, and `3xxN_A` `"oxygen atoms"`, where `N_A-=6.022xx10^23*mol^-1`. And thus, there are `2xx6.022xx10^23` iron atoms in such a molar quantity.

Now I know `N_A` iron atoms have a mass of `55.8*g`, and `N_A` oxygen atoms have a mass of `15.999*g`. How do I know this?

And thus `1*mol` of `"ferric oxide"` has a mass of `1*molxx(2xx55.8*g*mol^-1+3xx16.00*g*mol^-1)=159.60*g`.

Do you agree?