# Question #72e9a

May 27, 2016

$5.1 \cdot {10}^{- 3} \text{moles}$

#### Explanation:

All you have to do here is use Avogadro's number as a conversion factor to help you find the number of moles that would contain that many atoms of iron.

As you know, Avogadro's number tells you how many atoms you get per mole of a given substance. More specifically, you should know that

$\textcolor{b l u e}{| \overline{\underline{\textcolor{w h i t e}{\frac{a}{a}} \text{1 mole" = 6.022 * 10^(23)"atoms} \textcolor{w h i t e}{\frac{a}{a}} |}}} \to$ Avogadro's number

Simply put, in order to have one mole of an element, you need to have $6.022 \cdot {10}^{23}$ atoms of that element. This will be your conversion factor.

So, $3.1 \cdot {10}^{21}$ atoms of iron would be equivalent to

$3.1 \cdot {10}^{21} \textcolor{red}{\cancel{\textcolor{b l a c k}{\text{atoms Fe"))) * overbrace("1 mole Fe"/(6.022 * 10^(23)color(red)(cancel(color(black)("atoms Fe")))))^(color(purple)("Avogadro's number")) = color(green)(|bar(ul(color(white)(a/a)5.1 * 10^(-3)"moles Fe} \textcolor{w h i t e}{\frac{a}{a}} |}}}$

The answer is rounded to two sig figs.