 out a much better turnout than normal, I guess, because of the quiz. There's, remember there's a quiz today. It'll be at the end of class, so we'll do about a 20-minute lecture, and then I'll give you half an hour for the quiz. There's a sign-in sheet going around. For the online people that are here today, if you want to look at your test ball, the quiz is being taken by everybody else. You can come up here and grab your test, and we can talk about it after class. Online people, you have a different quiz. It's already online, okay? So it's been available since about an hour ago, this morning, and I think it'll be available until Wednesday at 10. So if I give you enough time to go ahead and do it, there's two parts. I think the first part, so I think this time you're going to have to set aside that there was some concern about the length of the quiz for the online people. So this time, to give you a little bit extra time, you're going to have to set aside about 45 minutes to take the quiz, okay? So that's for the online people. For the in-class people, of course you'll have a regular quiz. Okay, so the last thing we talked about was figuring out the oxidation numbers for various covalent compounds. Now let's look at figuring out the oxidation numbers for polyatomic ions. Okay, so this one that we have up here, unfortunately this part doesn't go with it. So let's just go over this one together. So HCO3 minus, okay? So this polyatomic ion. So hopefully you guys recall how to take or get the oxidation numbers of regular covalent compounds. This is exactly the same except where the covalent compounds, the total oxidation numbers are going to add up to zero. This is going to add up to the charge on the polyatomic ion. So they're all going to add up to negative one, okay? So hopefully you recall your rules for oxidation numbers. So how would you go about doing this? The first thing you would want to find the oxidation number, does anybody know the oxidation number of any of these atoms? Oxygen is what? Negative two, always, okay? So we go negative two like that and since we have three of them, right, we're going to multiply it by three, okay? Anybody know any of the other oxidation numbers here? What I'm going to do is what? Plus one. So we got plus one, minus six, right? We add those two together. That's going to be minus five, right? So minus five doesn't equal minus one, right? So what do we have to have here? What is the oxidation number for carbon? Plus four. Plus four, right? So if we go plus four, right? Plus one, plus four, plus five, minus six. Does that equal minus one? Yes? Okay, so if it asks us what's the oxidation number for carbon, we would say, of course, after we did all of this. So that's how you would do it. It's exactly the same as doing it for covalent compound except for with the polyatomic ions, of course they've got an overall charge, so you've got to equal all of these numbers to that overall charge. Okay, so let's continue our discussion about redox reactions. Remember, Leo, the line says gerb, right? So there are always going to be two reactants in a redox reaction. Remember the one we looked at yesterday or on Friday? Well, what's the oxidation state of zinc here? Does anybody remember from last time? The oxidation state from last time was for zinc? Zero. Why is it zero? Do you guys remember? You guys just looked at the elemental state, right? So whenever the atoms are in their elemental state, like Cl is in Cl2, or F is in F2, or zinc is in just zinc, oxidation number is zero. Okay, so just like copper here, oxidation number is zero. Okay, so which one of these things lost electrons? Zinc going to zinc 2 plus, or copper 2 plus going to copper zero? Hopefully you would say zinc going to zinc 2 plus lost electrons. And remember, when you lose electrons, you're oxidized. So zinc here got oxidized. So if I were to ask you which species was oxidized, you would say oxidized was zinc. And then if I asked you which species was reduced, what would you say? Copper. Copper. Copper, okay. Or you would actually probably want to say Cu2 plus, because that's actually what got reduced. Okay, so since we know that, remember reduced is GERG, gain, electron, okay? So now let's think about the concept of oxidizing agent and reducing agent. So in the redox reaction, the substance that contains the elements that gets oxidized during the reaction is called the reducing agent. So the thing that gets oxidized is reducing something else. Okay, so they're both acting on each other here. So since this is getting oxidized, zinc is getting oxidized, we call it the reducing agent, okay? Because it reduces the copper 2 plus. Okay, so zinc is reducing copper 2 plus. So even though it's getting oxidized, we call it the reducing agent. And then since copper 2 plus got reduced, or it oxidized zinc, right? We call this the oxidizing agent. If not, the oxidizing agent will always contain oxygen. Okay, in this reaction it obviously doesn't, but a lot of times it will. So the thing that gets reduced is called the oxidizing agent, and the thing that gets oxidized is called the reducing agent. So hopefully now you could go ahead and determine which is the oxidizing agent and which is the reducing agent. Again, a lot of times the oxidizing agent will contain oxygen. Okay, so in this one, and a lot of times the reducing agent is just metal in its elemental state. So you can hopefully just see this already. Okay, and see that water contains oxygen. Sodium is a metal in its elemental state, so it's probably going to be the reducing agent. Water's probably going to be the oxidizing agent because it contains oxygen, and in fact that's the case. I'll let you go ahead and go through this reaction on your own so you can figure out the oxidizing agent and reducing agent for yourself. So let's look at more general types of chemical reactions. So you can, all chemical reactions can be subdivided into essentially two groups, as far as you need to know. Redox reactions, which are reactions that we've been going over for this morning and last Friday, and non-redox reactions. So redox reactions are reactions where the oxidation number of the reactants changes as they go from the reactants to the products. Non-redox reaction is a reaction where the oxidation numbers don't change going from the reactants to the products. So you can then subdivide non-redox and redox reactions into three separate categories. Two of them, combination and decomposition reactions, are found as both non-redox and redox reactions. Double replacement reactions are always non-redox and single replacement reactions are always going to be redox reactions. In fact, this reaction here is a single replacement reaction. So let's go ahead and look at these different types of reactions. So we're going to learn to identify the following patterns of chemical reactions, combinations, decomposition, single replacement and double replacement. Single replacement, you can also call substitution reactions because you substitute one part of a substance for another part. Double replacement reactions, these are also called metathesis reactions. These types of reactions just go ahead and switch partners. So recognizing these various patterns will help you write and understand these reactions. So there's some evidence, visual evidence of a reaction occurring. You can go over this on your own. This is mostly good for when you're in the laboratory. How do I know if a chemical reaction has taken place? You can see a lot of times bubbles will come off as in the form of gas under a liquid. You'll get light shining off of your chemical broth, I guess. And you can also see a change in color a lot of times. Or heat is absorbed and produced. Okay, so let's talk about the different types of reactions starting with combination reactions. The combination reaction is just what's described here in the general reaction statement. It's the joining of two or more elements or compounds which produces a product of the different compositions. So you can have element A and compound B and when they stick together, you get compound AB. So an example of a redox combination reaction is this one here, S solid plus O2 gas goes to SO2 gas. Let's look at that in more detail and make sure we understand what's actually going on here and to say, oh, this is definitely a redox reaction. The oxidation state is these different elements and compounds. So does anybody know what the oxidation state of this is? Zero, right? Because it's in its elemental state, right? So that's zero. What about oxygen here? That's also zero, right? Why is that? Because it's in its elemental state, right? What about here? Are these going to be zero? No, why not? Is this an element? No, that's a compound. So you think they're going to have various oxidation states, right? Okay, so how do we figure out the oxidation state of these atoms in this compound? Okay, start with oxygen. What's the oxidation state of oxygen? Negative two. Negative two, right? How'd you figure that out? It's always negative two, right? So we go to negative two. Yeah, well, we're not going to have proxies in this one, so obviously we don't have to worry about it. We're going to have to take this... So what is the whole thing equal to? Right? Zero. It's not negative one, right? Because if we had a charge on it that was negative one, then the whole thing would be zero. So zero. So does negative two equal zero? No. No, so we've got to do other things to this, right? So is this all we've got to do to figure out all of oxygen? No. Because we've got a two there, right? We've got to multiply that by two, right? So that's going to be negative four overall. Does negative four equal zero? No. No. So what's the oxidation number of sulfur there? Plus four. Plus four. Plus four. Plus four. Does that equal zero? So that's cool, right? So let's look at what the oxidation numbers did. So for sulfur, did it change from products to reactants? Yeah, it did, right? And the products, what is it? All right, I'm sorry. And the reactants, what is it? Zero. Zero, right? Good job, guys. Zero. Fine. Okay, what about the products? What is it? Plus four. Did that change? Zero different than plus four? Yeah, definitely, right? What about oxygen? What's it like in the reactants? What's its oxidation number? Zero. Zero. And what about in the products? Minus two, right? Minus two, right? So let's look at this now in a little more detail, right? So can we tell that this is a combination reaction, hopefully? Right? Because we've got two reactants that kind of stuck together and made one product. Do you guys see that? So that you're kind of combining two things into one thing. And can we see that it's a redox reaction? Hopefully, you can see that it's a redox reaction. How do you, how can you tell it's a redox reaction? Because the oxidation numbers are different from the reactants to the products, okay? So that's how you know it's a redox reaction. So is this a redox reaction or is this not a redox reaction? It is, right? How did I figure that out? Because of what I just told you, right? The oxidation numbers change from what? To what? Not the actual numbers. From where to where do they change? Reactants and products are different, right? So the reactants got a different number than the products. So it's a redox reaction. Thank you. So what about this other one down here? Is this a redox reaction? Well, it says it's not. How would you be able to figure that out? How would you be able to figure if this is a redox reaction or not? Do the same thing as you did here. Let's do another one. Let's do this one here and prove to ourselves that it's not a redox reaction. So how will we figure out the oxidation numbers here? So are any of these in their elemental state? No. No. So you're going to have to figure out the oxidation number of every one of them individually, right? So oxygen is always going to be minus 2, right? So minus 2 times 3 is going to be minus 6. The whole thing has to equal 0. What is the oxidation number of n plus 3? How did I figure that out? This 2 times plus 3 equals plus 6, right? Plus 6 minus 6, does that equal 0? Yeah. Okay. So nitrogen here is... So nitrogen, oxygen and nitrogen, right? Reactions. Nitrogen is going to be... What's this oxidation state? Plus 3, oxygen. Minus 2. Minus 2. It's going to be minus 2 over here, too. From the products. So oxygen here is what? What's the oxidation state of oxygen here? Negative 2, always, right? Negative 2 times 2. Remember, the whole thing has to equal what? Zero. Zero, right? Yeah, we got it. Okay, so negative 2 times minus 2 is negative 4, right? What's the oxidation number of hydrogen in the compound, always? Plus 1. Plus 1. So plus 1 plus something, right? Minus 4 equals 0. So what's the oxidation number of nitrogen? Plus 3. Plus 3. So in the products, what's the oxidation number of nitrogen? Plus 3. Plus 3, right? Oxygen, what is it? What is it, guys? Plus 1. Is this a redox reaction? No. No, how'd you figure that out? Because the numbers are the same from the products, or the reactants of the products. Does that make sense? Yeah, so does that make sense? Okay, cool. So you already know how to get your oxidation numbers. You already know how to do that. We went over that on Friday in a lot of detail, okay? So this is just getting the oxidation numbers of each one of the components of the reaction and asking yourselves, did they change, did they not? If they changed, then it's a redox reaction. If they didn't, then it's a non-redox reaction. And you can tell, is it a combination reaction? Well, yeah, because two things went to one thing. Okay? Do you have one thing on it? No, so this coefficient here, this is just telling you that you got two of these things. Okay? So just that one guy will tell you what is redox. If you wanted to, you could multiply this side and this side by two. But when you do that, zero times two is zero, and zero times two is zero. So that's that coefficient that doesn't contribute to any of the calculations for the redox numbers of the particular molecules that you're interested in. Okay, let's look at... So here's, again, the combination reaction you can see. Again, this is a redox combination reaction. I'd like you to try to figure that out on your own. Hopefully some of you can already see that it is. And what the redox changes for those various compounds in the reaction. The last thing I'd like to talk about today before the quiz is decomposition reactions. So decomposition reactions are just the opposite of combination reactions where you've got a compound, A, B, that breaks apart, okay? Not necessarily in half, but it'll break apart to form two different things, okay? A and B. A, B is always going to be a compound, of course. A plus B can be either compounds or elements. So it's the reverse of a combination reaction. You produce two or more products from a single reactant. And you can have redox decomposition reactions like the one here. H2hi2hi gas goes to H2 gas plus I2 gas. Or a non-redox decomposition reaction like we have here. HCO3 aqueous goes to H2O liquid plus CO2 gas. And there you can see, well, there's peroxide for you. But I'll never make you figure out oxidation states for peroxide in this class because they're kind of weird. So you can see here, this is a decomposition reaction. This is the reaction that occurs when you pour hydrogen peroxide on like a cup. So single replacement, double replacement reactions we'll do over next time. So if you guys could close all your books. I don't think you'll need a period. Well, you may need a periodic table. You'll probably need to at least look up at that periodic table.