# Joni finds an iron horseshoe and notices how it as a fine layer of red flaky material. On closer examination, it is a fine layer of rust. Given that the horseshoe is 430g, calculate the number of moles of pure iron the original horseshoe had?

To a first approx. we know that there are $\frac{430 \cdot g}{55.8 \cdot g \cdot m o {l}^{-} 1} \cong$ $8 \cdot m o l$ of iron...........
But we don't know much of the iron horseshoe has oxidized with respect to its initial mass. Quite probably, this is a negligible amount, but we $\text{dunno a priori}$.