Why do vinegar and other acids remove rust?

I have started a project on restoring a very rusty knife. I had used vinegar to remove the rust. A question dawned on me: why does vinegar remove rust? So being the thoughtful person I am, I googled it. Unfortunately, Dr. Google could only provide me with what it is doing (which I already know).


But what I really want to know is: what chemical reaction causes the rust to disappear?




The acid can dissolve rust (e.g. $\ce{FeOOH}$). The chemical reaction is:


$\ce{3CH\_3COOH + FeOOH -> Fe(CH\_3COO)\_3 + 2H\_2O}$


EDIT: ($\ce{Fe(OAc)\_3}$is NOT soluble in water) The acid forms a water-insoluble salt with the iron oxide, which then *probably* just crumbles from the rust layer and precipitates in the container.


Mind that rust also contains for example $\ce{FeO(OH)\_3}$ and $\ce{Fe\_2O\_3·nH\_2O}$. The mechanism is the same.


Also, the acid oxidizes the upper layer of the iron under the rust to form a rust-resisting oxide-layer.


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Vinegar contains $\ce{CH3COOH}$ (acetic acid) which reacts with rust $\ce{FeOOH}$:


$\ce{3CH3COOH + FeOOH -> Fe(CH3COO)3 + 2H2O}$


and $\ce{Fe(CH3COO)3}$ (iron(III) acetate) is water soluble.


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