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](https://en.wikipedia.org/wiki/Rust), $\ce {Fe2O3·nH2O}$ 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.


Many colas contain phosphoric acid, and are quite acidic (Coke has a pH of ~2.5 according to [this science fair project](http://www.selah.k12.wa.us/soar/sciproj2005/Graphs/MarshalN.pdf)), thus they can dissolve the oxides.


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