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Offline tintinxx

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Rust Removers
« on: 09/01/2008 02:42:12 »
I have always know that acids serve as potent rust removers. What is the chemical basis for that? Acid-base reaction? Oxidation-reduction? ???


 

Offline Karen W.

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Rust Removers
« Reply #1 on: 09/01/2008 05:56:39 »
Vinegar is acidic.. that must be why it works so well on removing rust from metallic surfaces like tools and rusty hinges etc.
 

another_someone

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Rust Removers
« Reply #2 on: 09/01/2008 10:27:58 »
Not sure the acid actually even needs to attack the rust in order to protect it.

The problem with rust (and this is what makes iron different from a substance like aluminium or copper), is that the oxide (the rust) peels away from the metal, leaving exposed the layer beneath to be oxidised (if you compare this with aluminium or copper, they will both readily oxidise, but the oxide remains on the surface of the metal, rather than peeling away, and so will provide a protective layer that prevents the metal beneath from being exposed to oxygen).

All the acid really needs to do is provide a protective layer of salt on the surface of the metal that will prevent the metal beneath from being attacked (i.e. if the iron salt produced by the acid does not peel away from the metal in the way that the oxide does, then it will form a protective layer for the underlying metal).
« Last Edit: 09/01/2008 10:29:49 by another_someone »
 

Offline Bored chemist

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Rust Removers
« Reply #3 on: 09/01/2008 19:23:00 »
"attack the rust in order to protect it"
Pardon?
Vinegar can clean copper because the reaction of the copper oxide with the dilute acid is quite fast but the dilute acid won't react with copper (on it's own- in the presence of oxygen, it will)
Similarly the reaction of many metal oxides wiith acid is faster than the reaction of the metal.

In the particular case of cleaning rust from iron by the use of phosphoric acid not only does the acid react with the oxide rather than the metal, but it makes a relatively insoluble salt.
The reaction of the oxide with the acid is, as you sugested, an acid/base reaction.
 

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Rust Removers
« Reply #3 on: 09/01/2008 19:23:00 »

 

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