How does acid remove rust?
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.
