Question

Write net ionic equations for these reactions :
Cu^2+ + Fe ->
Hg^2+ + Fe->
Fe^3+ +Fe->
Pb^2+ +Fe->
Ag^+ + Fe->

and then the same but instead of Fe, addition of Cu to the six solution that I wrote before.. What ions are reacting in each case? please help me with this..

Answer 1

Look at the activity series of metals. A metal will displace any ION below it.
http://en.wikipedia.org/wiki/Reactivity_series

Answer 2

Along with what DrBob said, keep in mind that a more reactive metal will lose electrons (and thus become ions) when in the presence of a less reactive metal. These less reactive metals (the chart on wikipedia shows them as at the bottom) will thus steal any electrons needed in order to maintain a net charge of 0.

This is why gold never seems to diminish or lose its luster in comparison to other metals. It will steal ions from any metal nearby in order to keep from oxidizing, whereas other metals will oxidize (lose electrons -> increase charge #), or as we tend to know it, rust.