Well motherboars have a certain compatibility with processors. I'm not too savy on that, but obviously the newer processors aren't compatible with older motherboards. As far as it goes vetween Sandy and Ivy bridge tho, I've read somewhere that Intel mad the Ivys so they fit into Sandys' sockets, but I haven't had the chance to confirm that yet.
To sum it up, if your motherboard is old, you can't fit new CPUs in it, but if it's a swap from Sandy Bridge to Ivy Bridge then look it up yourself, you might be able to do that.