 Remember the test tube that we set up the first week of class in which we put some copper sulfate and some sodium chloride and an iron nail and you made observations for a week? Well now that we know something about electrochemistry let's see if we can figure out what was going on in our test tube. So let's empty the contents and see if we can figure out what's going on here. Now that we've cleaned up our mess you can see we have a nice piece of shiny copper metal so copper went from copper 2 plus to copper as a solid. The iron nail notice what's happened here it's gotten skinny so the iron solid is gone to iron 3 plus. You have some iron oxide rust that's coated down here but notice how small that is. So now you should be able to write two half reactions for one of the reactions that took place in our test tube over the course of the last few months.