# How many grams of iron are in 21.6 g of iron(III) oxide?

Aug 19, 2016

Approx. $15 \cdot g$ of metal.

#### Explanation:

$\text{Moles of iron oxide, } F {e}_{2} {O}_{3}$ $=$ $\frac{21.6 \cdot g}{159.69 \cdot g \cdot m o l}$

$=$ $0.135 \cdot m o l$ with respect to the oxide.

But by the composition of the oxide, there are thus $2 \times 0.135 \cdot m o l \times 55.8 \cdot g \cdot m o {l}^{-} 1$ $\text{iron metal}$ $=$ ??g.

An extraordinary percentage of our budgets goes into rust prevention; $\text{iron(III) oxide}$ is only part of the redox chemistry. Once you put up a bridge or a skyscraper, which is inevitably steel-based structure, it will begin to corrode.

Feb 7, 2017

There are 15.1 g of iron in the sample.

#### Explanation:

Step 1. Calculate the molar mass of ${\text{Fe"_2"O}}_{3}$

${\text{molar mass" = "2 × 55.84 g Fe + 3 × 16.00 g O" = "111.68 g Fe + 48.00 g O" = "159.68 g Fe"_2"O}}_{3}$

This tells us that there are 111.68 g $\text{Fe}$ in 159.68 g ${\text{Fe"_2"O}}_{3}$.

Step 2. Calculate the mass of $\text{Fe}$

∴ In 21.6 g ${\text{Fe"_2"O}}_{3}$,

$\text{Mass of Fe" =21.6 color(red)(cancel(color(black)("g Fe"_2"O"_3))) × "111.68 g Fe"/(159.68 color(red)(cancel(color(black)("g Fe"_2"O"_3)))) = "15.1 g Fe}$