Simple acids attack metals by their H+ ion. The atom from the solid metal gives an electron to the H+ and becomes a positive ion in solution while neutral hydrogen is formed, first as atoms then as molecules, which bubble during the reaction.
The electrode potential is a measure of how favourable this reaction is. Referring to the linked table: potassium is very prone to this attack, even in neutral water; zinc as well; copper is rather resistant; gold is very resistant. At + potentials you find noble metals, wearable as jewellery on the skin and useable as electric contacts, and which may even exist as metallic ore rather than oxides.
Some acids work through other means in addition to H+. For instance nitric acid is an oxidizer. Then the previous scheme doesn't apply easily.
Some (many!) metals also have different behaviours than expected from the electrode potential. Aluminium, titanium, chromium, tantalum... develop a hard and tight oxide layer that prevents the reaction. This suffices against sweet or sea water (aluminium), many acids (chromium), or most chemicals (tantalum). This mechanism is extremely dependent on tiny sub-details of the alloy and its condition; for instance 13% chromium make a steel stainless, but if the weld seam must resist corrosion we may specify <0.02% carbon rather than <0.06%.
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Topic: Copper (Read 4407 times)