# What makes cola efficient as a rust remover?

I actually tested submerging a bunch of old rusty knives blades in a cup of plain cola for a few days not expecting much. To my amazement the myth held true, coke is a really good rust remover.

So what is the chemistry behind it?

Rust consists of insoluble iron oxides and hydroxides, $\ce {Fe2O3·nH2O}$ and $\ce{FeO(OH)·Fe(OH)3}$. Acidifying these compounds protonates the oxide and hydroxide anions to for water:
$$\ce{O^{2-} + 2H^+ \rightarrow H_2O}$$ $$\ce{OH^{-} + H^+ \rightarrow H_2O}$$
This leaves the soluble iron $\ce{Fe(III)}$, which can be washed away.