okay so our heading is electrochem electron transfer again this is a 30 unit in the first chapters chapter 13 which is all the new information that you need the second chapter chapter 14 is all the applications voltaic cells which are batteries and electrolytic cells are kind of like batteries but they don't happen on their own we have to force them to happen so this is my intro slide to work our way into the oxidation and reduction key terms in this lesson so we're going to take a look at a reaction this is one of the reaction types from way back in science 10 this is a single replacement okay and a single replacement reaction is an example of electron transfer reaction we just never talked about it in science 10 being a electron transfer one to study whether something has electron transfer and is electrochemistry we need a track electron so that's the first thing i'm going to do i'm going to look up how many electrons each species has now to do that i'm flipping to the data booklet and looking up that atomic symbol so the very first thing we have is zinc zinc solid right you don't have to write this in but you have to realize that is neutral has no charge and if i look up zinc in your data booklet zinc has 30 electrons okay now what i'm going to do is put the total electrons on the bottom and on the top i'm just going to write the charge okay and in future examples i'm just going to do one of these two methods but i want to give you the visual of of the total electrons and how charge is a shortcut okay so zinc has 30 electrons has no charge uh if we look at hcl okay that hcl is a is a compound that is pretty close to being ionic and i'm going to treat it ionic as that h being a one plus and and a chloride one minus if you think of h plus well hydrogen by itself would have one electron but is h plus it has zero if we think look at that chloride that's cl minus chlorine is atomic number 17 and minus it would have one extra electrons out of 18. now there is a two in front all of the charges and the electron counts that i'm writing is just for one one of the atom or the ion so we've got a zinc of 30 electrons we've got an h we happen to have two of them they both have none and we have two cl minuses and they're both 18. okay now we're going to do the same thing for the other side when we get to the other side i see zinc again but it's no longer zinc neutral we now have zinc in an ionic compound that zinc is the two plus type now one way you could get that charge is to is to look up chlorides charge and figure out what zinc would be or if you look in your data booklet the only possible charge for zinc is is plus two so when i say your data booklet i'm looking at just the inside of the front cover it would be the very first page so that zinc is plus two so it no longer has 30 electrons it's down to 28 yes the plus two type okay uh next we got cl uh that's a cl and an ionic compound again that's not diatomic chlorine that's an ionic compound one zinc two chlorides well that's exactly the same as before we had a chloride back with a hydrogen in the beginning and we have a one minus cl and each of those have 18 electrons okay again i know there's two cls each has 18 it's not 18 in total last we have hydrogen now all molecules have no charge overall in terms of electrons i've been writing the electron count for each h here we've got two of them so you know h2 looks like that chem 20 bonding lines if they did a electron dot diagram that hydrogen has two hydrogen molecules two electrons no i've been writing the electron count for one of all of the atoms or ions so i'm just gonna there's two electrons and there's two h's so i'm going to divide that by two there's one electron for every h okay so we start with zinc with 30 electrons reacting with a hydrogen with none a chloride is 18 making a zinc with a 28 a cl of 18 and makes diatomic hydrogen with one electron each okay and now we can finally get at what's going on in terms of electrochemistry so we're looking for changes if i start of my zinc that definitely changed it went from 30 electrons at the beginning down to uh 28. i did that arrow a little further than i wanted there we go zinc to zinc we start with 30 we end up with 28 there is a loss i want to go minus two electrons with that zinc to go from 30 down to 28. now in a reaction we're going to see that whenever you have a loss of electron somewhere you have to have a gain of electrons somewhere else so somewhere electrons regained and that is with our hydrogen every hydrogen starts with zero with zero and they end up with one on the product side so there's a gain so i'm going to write plus one electron with the hydrogen okay now just to be super clear i'm going to put in or highlight minus one sorry minus two electrons for every zinc so i'm just going per zinc or slash zinc with the green it's plus one electron per every h there's two h's so in total there will be two electrons transferred but it's one electron uh each now you can track electrons like i did on the bottom using the total count but it's much faster and you get the same answer if you just look at the charge so if you look at the hydrogen going from plus one to zero okay you get the the same same type of trend so we've tracked the absolute change in each molecule what has happened two big things have happened zinc lost two electrons to become zinc two plus ion that was one that was the red the other key piece is two h pluses again two electrons one each to form molecular hydrogen those are our that's our gain and are lost and we always have to have this pairing now there's one other atom that never showed up in the so what happen statement and that is cl minus cl minus didn't do anything it started with 18 it ended with 18. so it's just a spectator ion okay there's no electrochemistry there's no gain or loss of electrons with our chloride so the point of this slide was to find the two pieces the gaining and losing of electrons and now i want to talk about well there are distinctive names given to these names first key fundamental definition this unit is largely a terms definition understanding type of unit there is some math and calculations but it's not a calculation heavy unit it's more of a theory heavy unit so reduction that by definition is a process where there is a gaining of electrons and an example we just did what gained electrons was the h plus when you gain electrons your charge goes down because electrons are negative the second key definition is oxidation which is the loss of electrons in the process that involves the loss of electrons in our example that was the zinc metal started with 30 electrons and lost two okay i'm going to highlight and that's going to be the theme for the rest of this this first lesson when you put the two together reduction and oxidation you get a redox reaction a reduction oxidation reaction redox the re from reduction sorry for the red from reduction and the ox from oxidation that's where the word redox comes from okay you must have something losing in something gaining not all chemical reactions are redox and that's something we'll address uh in a future lesson which type of reactions are redox and which ones aren't okay we just saw a single replacement reaction and all single replacements are redox so redox reactions are chemical reactions where electrons are transferred from one of the reactants to another one of the reactants okay in studying redox reactions and this is how your data table on page seven is built is by studying half reactions they're a balanced chemical reaction that shows either the gaining or the loss of electrons okay it doesn't show both okay the showing both would be a redox reaction showing just one of the two halves one of the two pieces the gaining or losing we call them half reactions and we're going to be writing lots of those and we're going to take a look at half reactions on the bottom of this slide so i'm going to put back up that reaction that we looked at on the previous slide and we're going to write out the two pieces next so i'm going to start with the oxidation so the oxidation or our new definition is that is the loss of electrons or the process that lost them uh so the loss was our zinc our zinc started with 30 electrons and ended up with 28. so we only need to show those red underlying pieces in the oxidation half reaction so i've pulled down those red underlying pieces okay so zinc solid is our only reactant and the oxidation half reaction producing the only product is zinc two plus but then we've got to show the electrons that aren't shown in the single replacement zinc going from neutral down sorry up to two plus involves losing two electrons okay any time electrons are lost they're going to be a product anytime there's a gain of electrons they're going to be a reactant okay so so i'm writing the oxidation electrons are lost here they're going to have to show up on the product side our other half reaction involves our two h pluses producing elemental hydrogen so that's what we see in the reduction half reaction i've pulled down the 2h pluses it requires the gaining of two electrons and we get our elemental hydrogen and i'm not going to write it out if we netted these two reactions together we would get the net redox reaction or actually i will write that out just so you can see it uh when we write redox reactions as you've been doing for years of single replacement and not even realizing it you never wrote the electrons in they always canceled each other out we have two electrons from the oxidation and they're going to cancel out the two electrons from the reduction so we don't see them in the net we just see the zinc that loses electrons the 2h plus that gained them we get the z our ionic zinc with the zinc after it's lost electrons and we get the two h's molecularly bonded to each other when they've gained now you'll notice in the net reaction there is no chloride showing up spectator ions disappear when you put two half reactions together because spectator ions aren't going to show up in either half reaction okay so we saw an example which led to our definitions of oxidation reduction next is a mnemonic how are you going to remember this oxidation reduction you just need to remember that leo the lion says ger and you'll be fine so leo helps me remember the oxidation part ger gaining electrons reduced that helps me keep track that reduction is the gaining part oxidation is a losing now with lots of practice you you'll stop maybe saying leo and gur i'm going to write leo and ger all through my notes as a reminder for you it's not something you have to know it's not something you have to memorize it's just a mnemonic uh so i'm going to do a couple more examples give you some skills or tools talk about your data table and how that can help you and then you're going to be ripping that reactions apart and figuring out what's the oxidation what's the reduction so for the last example of this intro lesson we're going to break apart understand the reaction of copper metal with silver nitrate and i'm going to do a couple things i want to write out two balanced half reactions so an oxidation and a reduction and i want to write out a balanced nat equation okay now that that won't have any spectator ions in it okay so i have to go back to my science 10 reaction type skills and think of which reaction type is this because i didn't list the products for you now we do have the reactants and words copper metal that's a metal by itself all metals except for mercury are solid at room temperature so that's where the solid came from and metals by themselves are neutral you don't have to write in the zero charge i actually would like you to write in the zero because a lot of students like to always write charges in with metals but when they're by themselves a metal has no charge when it's in an ionic compound it does have a charge so that's our copper part taking care of that the second chemical is silver nitrate uh silver in your data table is positive one nitrate is a polyatomic ion which is minus one so we just need one of each of those so that's why i wrote one silver and one nitrate now putting the ones in now i've got to predict the products before i can do any um redox analysis any thoughts what type of reaction do i have here i need to realize that in order to get products so there's five reaction types were combustion single replacement double replacement uh decomposition in formation and it is a single replacement okay so that's what i have to keep in mind so in single replacement the metals are going to switch places and we have to you know think of their charges so the copper is going to pair up with the nitrate now when it switches places with the silver and then the silver is going to end up all by itself now that copper isn't done i have to figure out what charge that copper is and that will then tell me how many nitrates i need so this is where i need to go to my data table right inside the first cover and look up what is the most common charge for copper hopefully somebody has their data booklet what is the most common charge for copper and it is plus two it has two types but the plus two is written first so this is plus two copper this is one minus nitrate so to make this balance i need two of those uh so now i've got the products out i just need to balance this whole thing and then i can start trying to figure out what's going on redox wise i got one copper at the beginning one copper at the end one silver at the beginning one silver at the end one nitrate at the beginning two nitrates at the end so to fix my nitrate i have to put a two in front of my silver nitrate that doubled my silver i double my silver at the end and now i've got my balanced equation so now i want to start diving into part a let's start trying to figure out what would oxidize and what was reduced so what was oxidized and their mnemonic to remember that is losing electrons is oxidized i'm going to throw in some charges that is silver one plus we've got nitrate a polyatomic ion i won't dive into all those pieces yet and i'll just label this is neutral silver as our product okay then no3 doesn't change at all and when we see something not changing the charge or the count of atoms in an ion there's going to be no electrochemistry there if we look at so what lost electrons copper started with zero and ends up plus two uh zero to plus two that would be losing electrons you have to lose two electrons to end up positive so what was oxidized that is our solid copper reactant okay so we're gonna have to write a half reaction with just the copper what was reduced so that's our ger what gained electrons that's going to be our silver it goes from plus one and it goes down to zero okay it gains one electron okay now again all these numbers are two electrons per copper and one electron per silver okay so what was reduced which reactant was it it's the silver uh plus okay i'm not going to include the nitrate it's just the silver that gained electrons so now i can write a couple half reactions uh knowing what was oxidizing what was reduced so i'll start with the leo so the oxidation which always has the electrons as a product we had solid copper becoming copper two plus and there's a difference of two electrons there our reduction our ger gaining electrons reduced so this better have electrons at the beginning we have silver and that's silver plus and that picks up one electron it gains one and then we get neutral silver you don't have to put the zero charge in but i really encourage you to put those in so that's part a done we figured out the oxidation we figured out the gaining okay last b what is the net well to get a net redox reaction you have to put two half reactions together so we're going to add the two half reactions but we do have to balance the electrons before we do it when we look at these two half reactions i've got two electrons in the first half reaction and i only have one in the second okay when we write half reactions they're always written with the lowest possible coefficients that's how half reactions on page seven are constructed and that's how you're going to learn to construct them when we net reactions up we often have to multiply one or both reactions to find the lowest common multiple of electrons in this case the lowest common multiple between two from the copper and one from the silver is two electrons i have two electrons in the top i have to double the bottom reaction to get two so i need two silver plus and two electrons producing two neutral silver okay the half reaction is the black the blue that i put over top of it is manipulating it to build the net and that leads to me being able to cancel my electrons to build my net and i end up with copper solid plus two silver plus producing copper two plus and neutral silver and our spectator ion of nitrate disappeared because it's not involved in any electron exchange what we're seeing here is the heart of batteries and that's what we'll look at in chapter 14. if you separate these two chemicals and make the electrons not go from chemical to chemical in solution but run through a wire you can power your iphone you can power um you know any electrical device you want and in today's world you can power an electric vehicle with the electron flow so a few uh skills tools for you and then you're going to be practicing uh in a couple minutes so the first big tool i was using and talking about is this data tape is your data table okay you're going to be flipping through this all the time in single replacement reactions like we just saw you'd have to be looking for copper to find out what is the most common charge now your group one and two metals are a bit simpler all the group ones are one plus and all the group two metals are two plus when they're ionic when they're by themselves they are neutral if you have sodium all by itself it's not plus one it's neutral it's only when you have sodium with something else that you have it as a charred species okay so to get charges that aren't listed in questions you're expected to go to your table you're going to see lots of polyatomics again like nitrate that we just saw and those names are all in that table so that's the first tool that's really useful essential for you to be looking up those charges the second key tool this is really blurry but this is your data table from page seven this is a table filled with reduction half reactions and you're always going to have this table on tests and exams okay so when you're back uh when we're doing uh our first quiz or our unit test at the end this is there for you and you'll see if you look in your table that whole silver half reaction is right there in your table and that copper half reaction we're just looking at is in the table but your table has them all written as reductions okay your table is built as a ger table a gaining table where all the electrons are on the reactant side and we'll talk even more about this table in lesson two the last thing i'll just highlight if you think of the forward direction of this table it is a reduction if you go backwards so if you think of you know starting with copper and going backwards that is an oxidation okay so it's a reduction table but you can get oxidation by working backwards