 So let's compare some different metals. So here we have lithium, here we have sodium, and here we have potassium being put in water. So if we have a look, we can see that potassium is reacting really, really readily. We can see the lilac flame of potassium being generated then exploded pretty quickly. So lithium, each little chunk of lithium is reacting relatively quickly. But if we had a similar size chunk of the lithium in the sodium, we would see the sodium is reacting a lot faster. You see the sodium forms a little ball and then it moves around on the surface. With the lithium chunks, they are still there and they're reacting relatively slowly. Further from with this is the hydrogen generated makes a bit of a casing around the metal, so it doesn't contact with water as much, so it reduces the rate of reaction. But if we have a look, we can place these metals on an activity series. So we've got potassium, which was much more reactive over here than the sodium was. So the potassium is more reactive than the sodium, and then the lithium would be further down again. Now sometimes you'll see lithium at the top of an activity series, and there's a very interesting reason for that. Now we're not going to go into it, but lithium does lose its electron relatively easily, particularly when we're looking at things like batteries, and that's why lithium is often found in batteries. But at the moment we're just looking at the reaction with water. So we can generate these metal reactivity series, and we can see that as the metals become less and less reactive, what they react with changes. So potassium, sodium, lithium, they were reacting with water quite readily at room temperature there, and calcium will do this as well. Something like magnesium, if you put it in water, it will react with water. It's just very, very, very slow, and you won't see the large amounts of bubbles being produced. And it will take a very long time for the magnesium to dissolve in the water. But all of these metals will react with acids, acids are quite reactive. So all of these metals here will react with acids. But again, as you go further and further down the activity series, the reaction is less vigorous. So we're going to have a look at magnesium and acid shortly. I'm reacting with oxygen, so oxidizing in oxygen. So again, all of these things will react. Potassium, when you take it out, it's kept in oil because it's so reactive. As soon as you cut it, it starts reacting with oxygen in the air and producing an oxide layer. So it's very, very quick. Whereas something like silver, silver oxide layers form over, it can be years, decades. This is why silver needs to be polished over time. But it's reacting with oxygen is very, very slow. When you have something like gold and platinum, they're both very unreactive metals. They don't react with much. So that's an activity series. So let's have a look at magnesium in acids. So this acid is hydrochloric acid. This one is of a higher concentration than the one on this side. We see as it's reacting, it's producing bubbles and those bubbles are hydrogen gas. And we're also getting a salt being produced, but that dissolves into solution. So we can't see it. So this one has finished because the acid is of a higher concentration. This one is taking a bit longer for it to go. So let's write the reaction. So a metal in an acid produces a salt and hydrogen gas. So we have magnesium. Our acid is hydrochloric acid. So we need to make hydrogen gas. Over here. And our salt is going to be the metal ion and the negative ion from the acid. So this acid is a chloride ion. So it's going to be MgCl. Now magnesium forms a 2 plus ion. Chlorine forms a minus 1 ion. So we only need two of the chloride ions to balance out the charge of the magnesium ion. And we've also got two hydrogens over here. So to balance it, two hydrogens, two hydrogens, two chlorines, two chlorines, and one magnesium, one magnesium. So magnesium is fairly reactive. So it will react with acid to produce a salt and hydrogen. That less reactive metal won't react, although it reacts slower. And indeed things like gold won't react at all. Gold can be dissolved in aqua regia, which is a combination of acids, but it's very, very dangerous. So now we need to compare vigor of reaction and activity. So here I have some zinc granules into that. We're adding some hydrochloric acid again. So if we want to compare vigor, we need to keep our other variables constant. The only thing we're going to change is the metal. So if we have the same quantity in concentration of acid, the same quantity in surface area of both zinc and magnesium. So these are the metals we're comparing. Which one would react more vigorously? So then you need to look at your activity series to figure out the answer. So here's magnesium. So a little dud there. And then here we've got zinc over here. So we're comparing magnesium and zinc. Magnesium is more active. So therefore we would see a much more vigorous reaction from the magnesium than we would from the zinc. Now in the case of the videos we've just seen, we can see it's a very vigorous reaction. We're getting a lot of hydrogen gas being produced. But the vigor does depend on the activity, as well as some of the other things like what we've got here, quantity in surface area 2 that can change the vigor. So that's right, the reaction of zinc with the acid as half equations. So the zinc starts off as solid zinc and that goes to zinc ions. We do make a salt. So the salt, the positive part of the salt is the zinc ions. Now zinc makes two plus ions and to balance that out we need two electrons. Okay, so we've got zinc making zinc ions and two electrons. Then we've got the hydrochloric acid that goes to hydrogen gas. So from the hydrogen and we get some chloride ions as well. So we're going to need two of these and two of these and now if we look at our charge we can see that we've got a charge of two minus on this side, so two chloride ions, but there's no balance over here for that negative charge. So we need to add our two electrons to this side to balance out what's happening here. So now we can write our overall equation. So zinc plus now we've got two hydrochloric acids here, two HCl, two electrons and two electrons on either side of the arrow, they'll cancel out. So then we go to zinc ions plus two chloride ions plus hydrogen gas. So now we've written that out. Now we could write that the zinc ions and the chloride ions as zinc chloride, which is the salt plus H2, and we can put our states in as well. So we have solid zinc hydrochloric acid is dissolved in water, so that's aqueous. If we go down here the zinc chloride dissolves in water as well, so that should be aqueous and hydrogen gas is a gas. So we can write the reaction of the acid with the metal as half equation minutes together like we would any other redox reaction.