# What is the actual formula for iron rust ??

May 28, 2017

$F {e}_{2} {O}_{3}$

#### Explanation:

Rust is just iron oxide, so it is made up of iron and oxygen. We can find the empirical formula (simplest ratio of a compound's components) by looking at the ions each element forms.
Oxygen forms ${O}^{2 -}$ ions and iron forms $F {e}^{3 +}$ ions. Now iron can actually form different ions because it is a transition element, but we usually stick to it being 3+ (if it forms a different ion then it will have the charge represented by a roman numeral after iron, e.g. iron(II) forms 2+ ions).

Compounds have an overall neutral charge, so we need to find a combination of iron and oxygen which results in their charges balancing out. This basically involves finding the lowest common multiple of their two charges - so for 2 and 3 this is 6, and so we have $\frac{6}{2} = 3$ oxygen ions and $\frac{6}{3} = 2$ iron ions.
This gives us the final formula $F {e}_{2} {O}_{3}$

Hope this helped; let me know if I can do anything else:)