Subject: Li, K, Ca, Na are only elements in activity series that replace H in H2O?

I am supposed to conduct a laboratory which asks the question "why don't 
Mg, and Fe replace H in H20 to produce H2 gas", but I am not really sure 
of the reason myself.  The lab has the students dissolving HCl, CuCl2, 
MgCl2, and FeCl3 in water.  Then they place Mg, Fe, and Cu in the 
solutions to see if their is a replacement reaction.  

I am guessing that hydrogen molcules may be displaced but are able to stay 
into solution because there is plenty of charge to go around?  If the 
hydroxides were taken out of the solution by precipation then it may be 
solubility of H2?  

Another good question would be:  How was the activity series constructed?  
If it was emperically constructed is there some theory to make sense of 
the order?

Please help!  Thanks, 
Rich

Re: Li, K, Ca, Na are only elements in activity series that replace H in H2O?