posted by Kiki .
A thin metal sheet is composed of Fe and Co
How do you ionize Fe to Fe2+ but not ionize Co ?
I tiried using the activity series of metals, but Fe is above Co, so anything that would ionize Fe would also ionize Co right?
So what JUST ionizes Fe but not Co?
You want to oxidize Fe.
One thing you can do, which may be overly complicated, is to treat the sheet and dissolve it completely with HNO3. That will oxidize both Co and Fe and place both in solution as their respective ions. Then, I believe Cd is between Fe and Co, and it will plate out Co metal while Cd goes in solution. Of course, then you have the Fe^+2 or Fe^+3 contaminated with Cd^+2 and that may not be what you want.