Question

How many moles are in 62 grams of iron (III) oxide, Fe2O3?

Answer 1

The formula that relates number of moles, n, and mass, m, is:

$M=\frac{m}{n}$

Where M is the molecular weight of the compound we are working with.

In this case, we have Fe₂O₃, and we can calculate its molecular weight using the atomic weghts of Fe (iron) and O (oxygen):

$\begin{gathered} M_{Fe_2O_3}=2\cdot M_{Fe}+3\cdot M_O \\ M_{Fe_2O_3}=2\cdot55.845g/mol+3\cdot15.9994g/mol \\ M_{Fe_2O_3}=(111.69+47.9982)g/mol \\ M_{Fe_2O_3}=159.6882g/mol \end{gathered}$

Now, solving the equiation for n and substituting the molecular weight and the given mass, we have:

$n=\frac{m}{M}=\frac{62g}{159.6882g/mol}=0.38825\ldots mol\approx0.38mol$

Thus, 62 grams of iron (III) oxide is approximately 0.38 moles.