Question

How many moles are in `"1.68 g Fe"`?

Answer 1

There is `"0.0301 mol Fe"` in `"1.68 g Fe"`.

There are `1.81xx10^22` atoms in `"1.68 g Fe"`.

Explanation:

Divide the mass of iron by its molar mass in g/mol to get the moles of iron.

`(1.68color(red)cancel(color(black)("g Fe")))/(55.845color(red)cancel(color(black)("g Fe"))/"mol Fe")="0.0301 mol Fe"`

One mole of anything is `6.022xx10^23` of anything, including atoms. Multiply mol Fe by `(6.022xx10^23)/("mol")`.

`0.0301color(red)cancel(color(black)("mol Fe"))xx(6.022xx10^23"atoms Fe")/(1color(red)cancel(color(black)("mol Fe")))=1.81xx10^22 "atoms Fe"` (rounded to three sig figs)