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If rust is found on metal, does acid eliminate the rust and if so what kind of acid?
Question Date: 2009-01-19
Answer 1:

Rust is what happens when you oxidize a metal. For example, you form Fe2O3 on Fe (when talking about iron or steel). Acid can dissolve the rust (Fe2O3). However, the acid will also oxidize the metal further, forming more rust, and dissolving that rust. In the simplest case, lets imagine hydrochloric acid and iron (HCl and Fe). When HCl encounters iron, whether it is oxidized iron (Fe2O3) or metallic iron (Fe), it wants to form iron chloride (FeCl2 or FeCl3). Therefore, when acid reacts with metal, it tends to dissolve both the rust and the metal, in order to form the iron chloride. However, if you were to carefully use dilute acid, you could dissolve away the rust before dissolving the metal.

Nitric acid (HNO3) will also dissolve the rust and the metal, but in a much more violent, caustic reaction. The oxidation reaction that occurs between the nitric acid and the metal forms NO2 and NO which are both gases, which both happen to be highly toxic.

I hope that this is helpful!

Answer 2:

Acid corrodes metal and releases gaseous hydrogen, leaving a salt behind. The kind of salt depends on the acid and on the metal. As far as I know, only hydrofluoric acid would be able to eat rust; its byproducts would be iron fluoride and water.

Answer 3:

Some acids remove rust (oxides), while others cause rust. Most acids will etch metal whether they cause rust or remove it. Phosphoric acid (H3PO4) is one type of acid which removes rust by converting it (iron III oxide) to a form which can be dissolved in water. Most other strong acids cause rust. Please note that some rust removers contain hydrofluoric acid (HF), which is extremely dangerous, since it penetrates your skin, destroys bone, and can cause heart attack, without you even feeling its presence. If you're using any kind of rust remover, read the label carefully and always wear goggles, chemical-resistant gloves, and protective clothing.

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