So far we've seen an example of an acid based reaction but the words acid and base have not yet been defined. In this lecture, I'll give several different definitions of the words acid and base. The first definition I'll give is the arrhenius definition of acids and bases. I'm going to first give some examples of arrhenius acids and bases. And then we will write the definitions up above. The first thing I'm going to do is write some dissolution equations. Something that we learned how to do last week. For example, what would the dissolution equation be for this compound? HNO3 which also has the name nitric acid. If we dissolve nitric acid in water the products would be H1+, which I'm going to call a proton. It's a hydrogen cation, isn't it? And the other product is the nitrate anion. So, if this is what nitric acid does in water, then an acid must produce what in water? It must produce the H1+ cation in water. How about a base? I'm going to dissolve the base in water so we can determine what's produced in water for, in the case of a base. The example I use here is potassium hydroxide solid. If I dissolve that solid in water, I can write the dissolution equation. And you see that the products are the, potassium cation and the hydroxide anion. So when we dissolve the base in water, it produced hydroxide in water and all arrhenius bases do that. So what we've done here is look at the species that this produced when the compound dissolves in water. And all arrhenius acids produce protons, or H1+, when they dissolve in water. All arrhenius bases produce hydroxide anion when they dissolve in water. Let me give you some examples of common acids and bases. Here are the names and strengths of some common acids. There are probably some species on this list that have names which are familiar to you. Things like sulfuric acid and hydrochloric acid you might have heard of just from everyday application. Some of the other things on the list might seem more exotic to you. For example, you might not have heard of chloric acid, or perhaps you haven't heard of boric acid. You've heard of acetic acid because that's the one that we used in the last demonstration. The formulas are listed here, and also the strength. And you see the first three listed are listed as strong. And then there's some that are intermediate. And then the last few on the list are listed as weak. What do we mean by acid strength? Well, in order to measure relative acid strength, what we do is we measure the extent of the reaction of that acid with water to form hydronium cation. Here's an example. Let's look at nitric acid, the first acid on the list, and the one that we used as an example of an Arrhenius acid. When nitric acid reacts with water, it reacts extensively to produce nitrate as an anion. And the proton gets transferred to the water. So that the other product is the hydronium cation. This reaction happens to such a great extent, that every time you add drop of nitric acid to water, all of the HNO3 species dissociates to make the nitrate anion, and hydronium cation in the solution. There's no undissociated HNO3 left, in the water at all. Zero. So we say this reaction is extensive, and that we call that, type of acid a strong acid. So the same is true s-, for sulfuric acid, or, hydrochloric acid. We're only looking at the transfer of the first proton. So let's look at sulfuric acid. [SOUND] Here's the reaction of sulfuric acid with water. And if we're talking about only the transfer of one proton, that leaves behind the hydrogen sulfate anion and hydronium as the other product. So again, that reaction is extensive, and we show that by having only a forward facing arrow. Hydrochloric acid reacts extensively with water to make the chloride anion and the hydronium. In the solution of hydrochloric acid and water, there is no undissociated HCL present. The only thing present is water, assuming it's in excess and it's a solvent, chloride ion and hydronium ion. So, that's the case where we have a strong acid. All of the acid reacts with the water. For a weak acid, on the other hand, let's just use a acetic acid because that was the one we used in the last, lecture as an example. In the case of acetic acid, when it reacts with the water, I'm going to write it the same way it's written here. The there's an H at the front to show the acetic hydrogen and then the other three hydrogens are not acidic. When that reacts with the water. This time, I'm going to use this arrow that shows both forward and backward motion. What's left over is the acetate anion and some hydronium. But in the case of acetic acid, there is some of the undissociated species present at equilibrium. In other words, the acetic acid does not completely react with the water, and only a few anions are produced. Which is why in the last demo when we did the demonstration, we saw that the acetic acid and the water had a dim glow when we submerged those electrodes in it. I can do another example, hydrofluoric acid, seems like it's related to hydrochloric acid and it is, but it's a much weaker acid. In this case, if I write the reaction of hydrofluoric acid with water, I have a large amount of undissociated HF at equilibrium. And only a small amount of fluoride and hydronium present. So that's how we determine the relative acid strength. The more of the undissociated acid that's left after we've added it to water, the weaker that acid is. And, the really strong acids react completely and extensively with water, so that all of the acid looses its protons. Okay, so that's acids, those are some common acids. There's lots of acids, thousand of acids, here's just a few. Let's look at some common bases. All of the bases I've listed here except for the last one are compounds that involve the hydroxide polyatomic ion, and even that one, when it reacts with water, makes some hydroxide. So if you see this combination of oxygen and hydrogen together as a polyatomic ion, that's your clue that you have a base. A lot of these bases can be purchased over the counter. You might purchase some Lye, or perhaps you purchase some Lime to put on your lawn. Maybe you purchase some milk of magnesia because your stomach's upset. In all of these situations when I add the base to the water. Let's use red for base. What happens when I add sodium hydroxide to water? Well of course it's going to dissociate, that's a strong base. That leaves me with sodium cation hydroxide anion and water. And it's the hydroxide anion solution that makes the species strongly basic. Some of the weaker bases. For example, let's look at ammonia, which we used in the last demonstration. When ammonia reacts with water, what it does, is it deprotonates the water to a small extent. I'm going to draw out the molecules in Lewis dot structure form like I did on the last example. That nitrogen is going to deprotonate the water. I'm showing that with this curved arrow, and that leaves behind this bonding pair on the oxygen now as a lone pair. So what are the products of this reaction? The products of this reaction that I've just written, are ammonium, NH41+. Plus hydroxide again. And it's that hydroxide that makes a solution, that excess concentration of hydroxide, that makes the solution basic. So in the case of ammonia, the extent of this reaction is not as great as it is for the case of the sodium hydroxide dissolving, and in fact, it wasn't completely correct to have just this forward facing arrow. I need to also have a backward facing arrow. So chemists are not always very careful when they use these arrows, but a forward facing arrow, let's just look at the different types of arrows that we can use to represent chemical reaction. This one way forward only arrow, really implies that there's an extensive reaction that only goes forward. It gets used a lot even when that's not the case, but that's implying that the reaction gives lots and lots of product. And there's very little reactant left. We can show reactions that go forward and backward two different ways. And both of those involve having an, either a single-headed arrow or a double-headed arrow facing in both directions. So these kind of arrows are to show equilibrium. And that implies that once we've reached equilibrium, there is a measurable amount or appreciable amount of reactant still there. And when you get to equilibrium the reactants turn into product at the same rate that the product is reacting to turn back into reactant. Alright, so that was a little side into the arrows. Let's look at some more examples of Arrhenius acids and bases. So another Arrhenius acid that we had on our list of strong acids was hydrochloric acid. When hydrochloric acid is put in water, it reacts extensively with the water to make hydronium. But there's another formulism that people use to show this reaction. Sometimes people use this formulism where they just show the ACL and split in half, to have the H1+ cation and CI cation. That's not actually what happens, but it's a formulism that people use all the time, so I'm going to use it here just so you've seen it. There's not any, actual H1+ cations floating around in the water. They're all associated with the oxygen of the water as hydroniums. So this particular way to represent what happens is not accurate, but people use it a lot so I'm going to use it here to illustrate this. One of the Arrhenius bases on that list was Sodium Hydroxide. And this is a relatively inexpensive but strong base that people use a lot in chemisty. If that is put into water it reacts to make, it reacts to the dissolve to make sodium cation and hydroxide anion. In both of these cases I don't think that it's been shown with the correct arrow type. The reaction of HCl with water should really be, a forward-only arrow. So I'm going to write over that. This should really only be a forward-only arrow, and the same is true for the sodium hydroxide. If we mix these two solutions together so I have a container of water, I'm just going to write water. And that water, one of the containers has the hydrochloric acid in it, and the other container of water has, sodium hydroxide in it. If we mix those two containers together, what would happen, chemically?
