 One of the most important skills of a scientist is to be able to make good observation and to design and conduct experiments in a controlled fashion. So we're going to do both of those things today. So what you're going to do is you're going to take sodium chloride, copper chloride or copper sulfate, an iron nail, either one that's been galvanized or one that is not galvanized. And we're going to set up a series of experiments. So it may be that you're going to design these and do them in your class, or you may be looking at them over time. But what I want you to do is to stop right now. I want you to pull out your notebook and I want you to sketch the first setup that we're going to do. All right? So we're going to take a test tube. I'm going to pour in some sodium chloride. I'm going to take a piece of filter paper and put in the test tube. And this is just to sort of slow the reaction down a little bit. And then I'm going to take copper chloride and I'm going to put about the same amount of copper chloride as sodium chloride. And we're going to take another piece of filter paper, put over the top of that. And now we have a choice of either the galvanized nail or the iron nail. So I'm going to use the regular iron nail for this one. Then we're going to fill this with water, set it aside in our test tube rag, and make observations. So that's the way we're going to set them up. But we want to look at all of the possibilities. Do you think it will make a difference if we put the copper chloride on the bottom and the sodium chloride on the top? Do you think it would make a difference if we used a galvanized nail rather than an iron nail? That's what I want you to discuss with your classmates. Then I want you to design as many different experiments that will control for all of the variables. Both the position, whether it's sodium chloride and copper chloride, or copper sulfate, iron nail, or galvanized nail. I would like you to use sodium chloride in every experiment, but only one of the copper salts in each experiment. So put on your thinking caps and decide how you're going to do this. All right, now here we have a number of permutations. So here we have an iron nail with copper chloride at the top, sodium chloride at the bottom. This is the same except it has a galvanized nail. This is the same except it has the nail pointing down. And this one, we've reversed the copper chloride and the sodium chloride. Over on this side, we have substituted instead of the copper chloride, we have copper sulfate. So we have copper sulfate and an iron nail. Reverse the sodium chloride and the copper sulfate, both the iron nail and then a galvanized nail. So these two, the galvanized nail is different. These two, the order is different. So now we're going to add water, and I want you to make observations. So what I'd like you to do is to record what you're seeing. All right, now an hour and a half has passed, and let's look at these and discuss them. I'm going to put a little piece of white paper so that it'll make it easier for us to see the colors of the solution. Notice the difference between the one that had the sodium chloride on the bottom and the one it had on the top. An observation you're going to make there. These two, the only difference was galvanized and non-galvanized. The difference between this one and these two was the nail was pointed down instead of the head being pointed down. In this one, the only difference between this one and this one is the sodium chloride was on the top and the copper chloride was on the bottom. So we're beginning to see some interesting patterns in the copper chloride test tubes. Now let's look at the copper sulfate. You're seeing some yellow down here. Where did that come from? Here we see several things that are different. There's yellow at the bottom, the solution is blue, and here the solutions are slightly purple. Also notice right here and right here there's a big space that looks to be empty, kind of like making a cave. So how do you explain how that empty space got to be there? You also notice there's some green color down here, what could be the green? And what's the color of this solution and the color of that solution? And what do you think the source of those colors are? This one looks more blue, that one looks a little bit more purple. The solutions over here seem to be almost clear. So what I want you to do is draw what you see, write down explanations for your observations, and we're going to hold on to these and come back and visit them in about a month.