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?


1 Answer 1


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.

Many colas contain phosphoric acid, and are quite acidic (Coke has a pH of ~2.5 according to this science fair project), thus they can dissolve the oxides.

  • 2
    $\begingroup$ It's not that Fe(III) gets washed away necessarily but that Fe(III) phosphates gets formed which works afterwards as a protection layer like the oxides for e.g. aluminium. $\endgroup$ Jul 10, 2015 at 8:46
  • $\begingroup$ Ah, yes. I didn't think about the phosphate ion. Good point. $\endgroup$
    – buckminst
    Jul 14, 2015 at 19:08
  • $\begingroup$ It's not just a point but what happens :) $\endgroup$ Jul 15, 2015 at 1:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.