Formation of metal ions when metals dissolve
Posted: Sat Feb 07, 2015 10:40 am
Is it correct that when metals are dissolved in an aqueous solution by an acid the metals always form ions and lose electrons in the process?
Re: Formation of metal ions when metals dissolve
Posted: Sun Feb 08, 2015 1:29 pm
Your question implies its answer :)
When a solid metal is dissolving, it must be turning from a solid (standard state with oxidation number of 0) to its aqueous form (a cation with a positive oxidation number). In order for a pure metal to go from a solid to an aqueous ion, it must lose electrons. If you look at the periodic table, the first two columns are alkali and alkaline earth metals and, based on our periodic table rules of ions most commonly formed, they form cations. To see if a metal will be dissolved by an acid, you can look at an Activity Series which lists elements from easiest to oxidize to hardest to oxidize. When a metal dissolves in acid, it is being oxidized by H+ ions. Here is an activity series:
K > Ca > Na > Mg > Al > Zn > Cr > Fe > Ni > Sn > Pb > (H) > Cu > Ag > Hg > Au
Hydrogen is included as a reference point. All metals above hydrogen on the activity series are easily oxidized and can be oxidized by H+ ions (meaning they dissolve in acid). All of the metals less than hydrogen are difficult to oxidize and are not oxidized by H+ ions (meaning they do not dissolve in acid). These are called "noble metals." All metals that are able to dissolve in acid form positive cations and lose electrons.