Transcript for:
Understanding Redox Reactions in Galvanic Cells

good day everybody uh welcome welcome once again and uh on this very very cold uh day in south africa and hopefully for the rest of you in other parts of the world hopefully the weather is much much better where you are all right so today i want us to cover uh redox reactions in galvanic cells so i'd never really um made um just a theoretical explain the theoretical aspect of this so i just thought i'd just make a video so that you would understand the fundamentals of redox reactions right from the beginning so if you haven't subscribed please make sure that you do the right thing and just give us a thumbs up if you like the lesson um but let's just get right into it okay so first of all um when we talk about raydoc's reactions right let's talk about that with redox so the word redox is actually a compound word or it's just an uh it's made out of two abbreviations essentially right so redox comes from the two words reduction and oxidation okay so we have what we call reduction okay now what is reduction by definition we say that reduction is the gain of electrons all right we're going to talk about it just now so we're talking about the gain of electrons okay and we've got the ox part which talks about oxidation okay so and we actually say that oxidation is the loss of electrons so um these are the two definitions of uh reduction and oxidation so here it's the loss of electrons if you don't mind i'm just going to use the e minus to designate electrons right so now what's simply happening in a redox reaction is that we are actually exchanging electrons so this is a reaction that involves a transfer of electrons okay hence uh at a later stage we actually now talk about electrolysis okay so in this case uh what we are simply doing is we are having electrons move from the one um um electrode um to the other electrode okay so um just quickly let's talk about the structure of a galvanic cell just to quickly show you okay so a galvanic cell basically usually is made from two beakers okay or two containers and what we have is that we've got an electrode okay so an electrode uh usually made out of metals but of course you can have a you can have a guess okay so what happens is that you'd obviously have a wire put a voltmeter there okay just to measure the two and we put it in an electrolyte so this is a soluble substance and i'm going to talk about it just so that you explain you you understand it as we go on and then usually they use at last youtube for this okay you've got a salt bridge where they take a very high highly [Music] soluble salt highly concentrated salt and then you'd have plugs here porous plugs right like something like cotton wool um or whatever that may be right so essentially uh in a galvanic cell this is this would be the structure now we call these guys electrodes okay just keep that in mind so this would be an electrode and this would be an electrolyte now please remember what i said to you uh electrolyte okay sorry i'm squeezing that in there okay so we'd have an electrode and an electrolyte of course the same is true for this site okay you've got an electrode electrolyte there remember that we say that the electrode has to be a and a soluble uh solution okay now ladies and gents this is just our secret please don't tell anyone right um the rule of thumb is the following whenever i give you a metal there whatever metal it might be okay let's say zinc for argument's sake okay so um what electrode can you possibly or electrolyte rather can you use so if i give you zinc for argument's sake so um you use the nitrate of that particular metal well why am i advocating for nitrates well all nitrates are actually soluble right uh um some of the chloride salts are not solid soluble like silver chloride it just makes precipitates right and that are not soluble um some sulfates may not be soluble but uh we know that all nitrates are soluble so for argument's sake if i were to give you lead on this one okay which electrolyte would you use there lead nitrate okay so just remember um just as a rule of thumb should they ever ask you about the type of electrolyte that would be used there okay please always advocate for nitrates okay right now uh we said we've got uh electrodes we've got electrolyte now i want you to please note we said this is at last youtube and we put porous plugs cotton wool uh anything like that that doesn't allow solids to flow to move through but it does allow liquids to flow through so it's a it's a semi-permeable uh sort of membrane right or substance so in this case um what do you do in the salt bridge you put a highly concentrated salt okay um so you know it could be potassium nitrate um you know you you try and use something that is relatively soluble so um potassium nitrate works quite well uh of course there are other types you can even put sodium chloride today right uh just as long as you make sure that the chloride um uh element or rather um salt uh would not form a precipitate in any of your half reactions okay right now what i want us to quickly do is i want us to quickly look at how actually does these reactions uh actually perform how uh does reduction take place oxidation take place how actually do you know which electrode is your uh um anode okay so what we normally say is that the one that undergoes reduction okay we call that the cathode all right so we say that the electrode okay any of the electrode that undergoes reduction now please i want you to notice the one that undergoes reduction we call that the cathode okay and i'm just going to throw a contrast there between this cell as well as the electrolytic cell so that you understand exactly what the difference is and why i emphasize what i need to emphasize on the electrolytic cell okay now we say that okay reduction occurs at the cathode now if you want to you can just remember the red cat okay i used to have a red cat bothering me at my house so okay i'll remember that quite well so red cat okay so um you remember that reduction occurs at the cathode and then we say oxidation occurs at the anode okay so let me use a capital letter there all right so reduction occurs at the anode now ladies and gents let's talk about the physical property or the physical part of this okay how would you know that uh one of the substances undergoes reduction okay well generally speaking we say well when it undergoes reduction there's actually a gain in mess okay so this one will actually get bigger and bigger and you'll see why as we um do the cell right so this one gains mass all right so as it uh has more electrons coming on to it as it undergoes reduction okay so it gains mess and obviously this one loses mess okay right so this is just the uh theoretical aspect of things uh so that you can just know how to generally navigate okay now notice once again here it's gaining is gaining electrons so in in effect it means that electrons are being received over here all right so this one is losing electrons okay so this is where my electrons are made and they're sent out to the other one okay so as a result uh it will lose mess in the process okay so that's the theoretical part now i want you to please note that first of all galvanic cells okay the energy conversion that takes place in a galvanic cell is from electrical um sorry chemical energy right so a galvanic cell basically uh converts chemical energy into electrical energy i want you to please remember that okay electrical energy so that's what a calvinic cell does now notice this it means if i'm going to convert chemical energy so a chemical reaction takes place and obviously energy electrical energy is given off so it means that this has to be a spontaneous reaction okay just please remember that so it means that this reaction takes place on its own all right so it means these chemicals as soon as they see each other all they simply do is that they want to react and then suddenly uh in this case some of the energy that is uh uh um you know given off there is electrical energy it's it converts it into electrical energy so remember that this would happen spontaneously so it means uh you don't need to put an external source as spontaneous okay so um it means in this case it would therefore convert it into electrical energy all right now just one other thing that i want us to um to remember is that uh please note so we say the substance that undergoes reduction we did say that's the cathode so remember redket so we said the substance that that that undergoes uh oxidation the substance which means the electrode that undergoes oxidation is the anode so if you can just remember an ox okay an ox you know like mo all right so an ox or you can just remember that the the the vowels go together a and o right so in this case we know that it takes place at the anode now ladies and gents uh just one other thing that i want you to please note so the electrode that undergoes reduction okay we usually call it the oxidizing agent i'm going to explain this just a bit uh oxidizing agent now the moment i put agent there it seems to sort of you know you kind of flip the script in a sense so the one that undergoes reduction we call it the oxidizing agent and obviously the one that undergoes oxidation we call it the reducing agent okay right we'll we'll get to it in just a little while uh reducing agent okay so it's important for you to get these fundamentals so that uh you would know how the cell operates okay so we call this the reducing agent now i want you to think about it just a bit okay in order for electrons to be gained right the one that gains electrons why does it gain electrons it gains electrons because someone has given off those electrons okay so if you think about it in order for me to gain electrons right i am the one that enables okay electrons uh uh rather i am the one that causes this one to lose electrons why because i want them okay so that's why we say it is the oxidizing agent it causes electrons to be lost why because it's demanding electrons okay so the moment you use agent remember it means uh you know an agent is not the one that does the thing but it just simply facilitates the process right so um in this case when you look at oxidation right so in order for electrons to be lost or for this one to give away electrons right it's because someone else wants them right so it means uh this one all right uh uh um it's giving electrons so that the other one can actually gain them so it is the reducing agent it's the one that causes reduction to take place why because it's giving away the electrons so uh just remember that once the moment that you use agent there okay uh it kind of flips the script a bit okay right so um please i want you to remember that this is important theory okay um of course the most important thing is for me to now explain this now the the way that i want to explain it is i want to take an example um you know of a cell that exists okay and i'm going to show you how this process takes place okay but now let me just quickly let's assume that the cell that we have is a zinc copper cell and i'm going to take zinc and copper okay copper 2 plus right so in this case we're simply saying okay if you've got zinc and copper now i'm going to show you from the standard reduction potential table so that i actually show you what these uh reduction potentials actually mean okay so let's pull it right there okay and there it is over there okay so uh this is typically what our table looks like okay uh by the way it doesn't matter you've got two of them usually for those of you in south africa you've got two of these tables you've got the a and the b but it's essentially the same thing right now i wanted to note in this table that we're given here you've got some of those reactions there half reactions okay and you see next to them there's a an e standard value and those values are positive right and as you go down the table okay depending on which table you have there as you go down can you see that those values now tend to uh towards the negative okay now what i want us to talk about quickly is why is it that some of them become positive and why that becomes negative of course whether you fully understand that is neither here nor there for the exam but i'll show you actually a quicker way to um to actually answer those questions okay right now let's get into that quickly and look at why those values are positive and why some of them are negative now ladies and gents um we usually use what we call a standard hydrogen electrode okay uh i'm not very good at drawing okay so you'll have to forgive me for this i'm about to commit a crime just now okay so um if you think about uh hydrogen okay so it would look something like this so they use platinum over there okay now think about it uh um hydrogen is a gas right okay so it's not easy for a gas uh to give away electrons or in this case um uh you know to to be able to transfer electrons to metals so what happens is that we use platinum over there and what the platinum actually helps us to do uh remember that uh platinum is an you know it's an inactive you know we we call it it's chemically inert all right so it does not react with the elements over there right so um platinum actually just enables us to have electrical contact okay so as that hydrogen so you'd have hydrogen in here we're pumping hydrogen over there okay so there's a hydrogen coming in okay and so let me just show there are some bubbles over there so this is the standard hydrogen cell and of course you'd have an acid here and remember what an s it does is that it gives us those h plus ions now if you remember for those of you who have done the afbar principle right um let's talk about the atomic structure of hydrogen so hydrogen has got a uh an atomic number of one so meaning that in its nucleus okay as i said i'm going to commit a crime just now okay so in its nucleus it's only got one uh proton in the nucleus and as a result it's also got one electron okay uh on the outer shell okay so i'm just making a a structure of a of an atom there right okay so um if you think about it now for hydrogen okay for it to become chemically stable it can actually give away this electron all right it uses the same amount of energy to give away that electron and so satisfy the half bar principle uh um remember for something to be chemically stable uh you'd need to satisfy that 2n squared right so which n uh it's the energy level so this is the first energy level okay but you can have zero energy levels it means that you can get rid of this electron and you'd have zero over here or you can have a energy level number one now in order for something to be chemically stable right at energy level number one you'd need to have so that's this would be two times one squared okay so in this case you need two electrons okay now ladies and gents if you don't understand this that's okay that would be another lesson for another day okay and probably i'll do that when i go through the grade 10 content okay so what you need to know is that hydrogen uses the same amount of energy to either gain an electron or a uh you know to give away an electron so in this case we say that hydrogen therefore becomes our reference now let me tell you why okay so it becomes a reference why because hydrogen says i don't mind i can either give away an electron or i can receive an electron it doesn't matter right so whatever it is that it reacts with right hydrogen would say what do you prefer do you prefer to give away electrons okay so therefore i will gain electrons okay uh if you if if the other substance says no no i prefer to gain electrons then hydrogen says no no no i'll prefer to give away therefore electrons so in a sense hydrogen becomes our reference now please i want you to note okay now we talk about the standard conditions that's why you'll see in the table that i gave you there okay we we talked about standard reduction potentials okay so uh if you look at the top of that table okay it says standard reduction potentials can you see that right now why do we say standard now ladies and gents please i want you to note very important so we say that there are standard conditions that this cell needs to operate under okay now we've got the following condition condition number one is that we must have a temperature of 25 degrees celsius okay so we call that room temperature so that's the first condition so when they call those standard conditions it means these cells will give you those those values under these particular conditions that is okay a temperature of 25 degrees we said that's room temperature okay and secondly um we say that the next standard condition is concentration right of your electrolyte so initially the concentration of your electrolytes must actually be one mole per cubic decimeters so it means in order to generate the numbers that we see in that standard potential table right you must adhere to those conditions that we have over there right so that's room temperature that's a concentration of one mole per cubic decimeter and particularly now uh ladies and gents only if one of your electrodes is a guest will you mention this these are pretty much standard okay those are these are always there however the next one is only applicable if you've got a guess we say that uh the standard pressure must be one atmosphere it means that that would be around at 101.3 kilopascals or you can just simply round it off to 100 kilopascals okay so that's one atmosphere of pressure okay so that's 100 kilopascals so it means when we operate these cells all right so these cells uh will give us those values under standard conditions so the emfs that we have there will operate under standard conditions and those are the standard conditions okay now say for argument's sake now i want to take uh the first example say i take now please i want you to look at this all right so it means if i were to take a standard uh potential okay i take um let's say i take zinc okay i'm gonna take zinc over there so uh here's my hydrogen cell okay now here's my hydrogen cell and on the other one i would put let's say we put zinc okay right now what's going to happen in the cell so say we've got zinc over there right so we say this one the hydrogen cell is our reference now please i want you to listen to me carefully and i'm going to show you where this comes from so therefore when you've got zinc and hydrogen all right you'll see in your standard potential table okay let's find zinc okay so there's zinc over there that's negative 0.76 now what does that number actually mean all right so it means zinc with hydrogen if i were to connect it to a hydrogen cell zinc says no no no i don't like going that way why because you see when you say negative it means it's losing energy right so if it's losing energy going that way so if i wanted to to imagine it this way um think about you know going uphill right if you are going uphill you need to put in energy yourself in order to go uphill right but if you're going downhill you don't even need to put an effort you just simply go there on your own spontaneously so it means zinc going that way undergoing in this case reduction zinc says ah i don't prefer undergoing reduction why because i lose energy it's like going uphill right so what does ink do it says nana i prefer actually undergoing oxidation going that way because in that case it's like going downhill for me in that in that return in that regard okay so if you think about it so zinc with hydrogen so if i were to take a hydrogen cell zinc would say no no i prefer to give away electrons okay so therefore hey take those electrons you hydrogen okay so zinc would actually undergo oxidation all right because it says it's easier for me to go to get oxidized why because it's like uh going downhill for me right so zinc would actually force to give away electrons and therefore hydrogen or the hydrogen half cell would now be forced to accept electrons right so remember all that it simply does is that it's simply saying hydrogen is saying i don't i can take anything whether you want me to receive electrons or to gain electrons tell me what you prefer you are the boss okay so in this case zinc says ah i prefer to give away electrons and so zinc gives away electrons and in this case uh the hydrogen half cell would therefore gain electrons and that's why this cell or rather this table is showing you that going that way giving zinc or zinc iron electrons it's like you are forcing it to go uphill all right but if you wanted to lose electrons that's like oh it can do that spontaneously it can do that very easily when it's with hydrogen okay right so let's take another example uh say for argument's sake and let's take silver so if you were to replace a zinc with silver okay hydrogen again asks the question silva what do you prefer for me to do all right remember hydrogen says i can do just about anything that you want me to do okay right so um silva says ah you know what i prefer to gain electrons how do we know that it prefers to gain electrons because going that way right look at that it now uh um uh so it get gains energy right so for zinc i mean for silver rather it's easier for it to actually undergo reduction receive electrons and as a result um become the metal all right why because in this case it gains electron it gains energy it doesn't lose energy right okay so in this case we're simply saying okay if it were to react with silver silver says ah i prefer to undergo reduction i prefer to go that way so that i can gain okay who doesn't want to have more hey right so in this case so that i can gain energy so that i can become a stable right so um for silver going downhill is actually gaining electrons all right so if it were to react with the hydrogen so hydrogen would say all right because you receive you you prefer to receive electrons i will therefore give you electrons so that you can receive electrons so in a sense ladies and gents to try and help you understand this okay you've got some that prefer to gain electrons okay those are the ones that are over there with the negative okay uh sorry uh so those are the ones with the positive rather so they prefer to gain electrons they prefer to undergo reduction okay whereas the ones at the bottom over there well depending on which table that you are using okay so the ones with the negative okay they prefer to lose electrons look at that look at our hydrogen can you see it's got zero over there so hydrogen is simply telling you ah man anything goes for me whether you give me electrons or you gain electrons it's actually all the same for me okay right now uh perhaps what we should do ladies and gents is that let's take a typical example okay just to show you how to therefore uh answer questions or to actually uh just apply this theory on um on the calvinic cell okay so shall we we're going to take a zinc copper cell and i'm going to show you how to answer questions now let's look at a um a zinc copper cell so there it is there just made it easier for us okay so uh say we've got zinc and copper all right and i'll use copper because uh there's a warning that i want to give you uh just a little later on right so just quickly what happens on the one-half electrode okay on the one-half cell rather okay so on this side so remember we said we've got an electrode and we've got an electrolyte right so what would you typically put there as an electrolyte now remember that zinc zinc would be would have generally speaking an oxidation number of two plus so there it is over there zinc two plus that's the ionized version of it okay so zinc two plus so in this case because it's got a two plus to right zinc nitrate uh zinc nitrate would be zn no3 okay with a 2 over there why does it have that 2 because the nitrate ion has got a 1 minus so you need 2 of these to bond with one of that okay so that's zinc nitrate if you think about copper as well just be careful about copper ladies and gents that's the warning i wanted to give you all right so the examiner would kind of show you which copper you need to use and how do they do that uh they actually usually just write down the electrodes over there uh rather than the them the ions over there so if they they use for instance copper two plus over there so what they are telling you is that uh they want you to take the one with the two plus and copper zero which means the solid okay all right so uh you check there so copper look at this one this one is copper two plus but check on the other side it's copper plus i hope you can see that right so copper two plus and copper plus so it can't be this one but there's another one that says copper two plus and copper zero so it has no number there so there's a zero right so copper two plus and copper zero and that's the one that you want okay so it's got a potential of plus 0.34 okay so please just typically just check uh which copper they wanted to use but which electrolyte it's copper here so which electrolyte are we going to use uh almost wrote zinc again so this is going to be copper nitrate okay and in this case this is what we have okay right now remember we said we've got a uh we've got a highly concentrated salt there uh by the way i must just emphasize what is the function of our salt bridge so just remember that okay uh what do we use the salt bridge for when we say that the salt bridge first of all it neutralizes excess ions you'll probably understand that so it neutralizes excess ions excess ions and secondly we say that it actually completes the circuit right uh so it allows for ions to move so it completes the the second so completes the circuit rather okay so it is the one that enables for this to be a closed circuit right so and by the way without that salt bridge the cell wouldn't be able to operate okay so now ladies and gents i want you to please note okay that the zinc nitrate over here makes it such that you've got zn two plus ions okay remember that a salt uh a soluble salt what it does is that it will ionize okay so there's lots of zn2 plus ions over there okay and on this side there's copper nitrate so as a result there's copper two plus ions i want you to just remember that uh because we are just going to interfere with that okay right now what we are going to do is look at our half reaction and half reactions okay so we go to our standard reduction potentials table all right please i want you to follow me on what i'm going to do i am going to find zinc and copper from my reduction table okay so there's my zinc over there so zinc two plus plus two electrons giving me zinc that's minus zero point seven six so i'm gonna write it just as it is right so this is zinc two plus plus two electrons and that would give me zinc okay and we've got a potential of minus 0.76 volts okay that's obviously when it reacts with hydrogen it would have that potential right so uh what about copper writing it as it is copper two plus plus two electrons and that would give me uh copper there and i get positive 0.34 volts now ladies and gents how do we then um how do we actually uh get you know the reaction that actually takes place so i want to know which one will undergo oxidation that is which one will uh um give away electrons and which one will undergo reduction and i want us to also decide which ones are our which direction will our cat ions move our n ions and all of that all right now please i want you to stay with me as i do this uh uh as as we go through this section right so you noticed i copied everything as is right so now all i'm simply going to say ladies and gents is just draw a number line for yourself and say well which is the smaller number between the two okay mathematically speaking which is the smaller number i'm sure you can actually see you you remember that we start with or you know the more negative the number becomes the smaller it is right so it means i'm going to say okay i'm going to start with minus 0.76 here i'm deliberately taking my time so that you'll know how to actually answer questions here so obviously it means the other number so you always write a number line in ascending order right so it means that your numbers increase that way so i started with a smaller number and the bigger number on the side okay right and i want you to see what i'm going to do very quickly right so we say well in this case okay uh there's usually an mnemonic that i use uh but i'm going to shy away from it so that i don't become very controversial right okay so in this case we normally just say okay so if you think about letters of the alphabet okay we say it's as easy as a b c right so i'm gonna do that so as easy as a b c right okay you can use that as your b the middle part okay so this one becomes your a and this one becomes your c now what does that stand for a do you remember the anode okay so therefore it tells me this guy is the anode and so therefore this one becomes the cathode that will always be applicable for as long as you've done the right thing over there so that will be the case right so that's your anode and that is your cathode okay right and what happens at your anode in your cathode you must please always remember that uh your electrons will always move from the anode to your cathode okay so in a calvinic cell obviously we know that we'll always have electrons moving moving from anode to cathode okay so uh usually for my learners i just teach them about the anc rule okay saying that it gives away houses right but obviously i wanted to shy away from that right so in this case uh we're simply saying all right so that's as easy as abc right and we know electrons will always flow in that direction now please i want you to note all i'm simply going to do ladies and gents the anode on the anode half reaction okay so on the anode half reaction so which one is my anode remember where does the negative 0.76 come from it's from the zinc right so i know it means that zinc is my anode it means that copper is my cathode can you see that okay so now the one that is the anode i'll always take the half reaction of the anode and i will just simply turn it write it the other way around remember the anode gives away electrons so this guy said i don't like going that way so i am actually going to prefer giving our electrons so the anode you always take the reaction of the anode and you write it the other way around so what was on the left will now be on the right so please note the difference now it goes from zinc and with one arrow you see it had a double arrow over there right so now only with one error it moves from zinc and zinc two plus plus two electrons so i took that reaction and i actually just swapped it around like that okay just please remember so this is the half reaction that takes place at the anode so then i take the cathode cathode i will leave exactly as it is so the one that is the under on this side the cathode i'll take it exactly as it is so that's going to be copper two plus plus two electrons the only difference now instead of a double arrow i just will only have one arrow okay now i want you to see what is happening over here ladies and gents so all it's all that's happening is that it's saying to you zinc moved from being zinc and it became zinc two plus by giving away electrons you remember that we said the anode is the one that undergoes oxidation and ox right and then cathode copper two plus received electrons and in this case will become copper now all i'm trying to show you ladies and gents is that and now you can write down what we call the net ionic reaction or the net cell reaction okay so all you simply do is you must always make sure that the electrons are the same on either side so we've got two electrons over here two electrons there so they're equal so we can cancel them out right number of electrons given equals number of electrons received and i'm going to write down everything now that's on the left hand side so what am i left with it's going to be zinc plus copper two plus okay giving me now everything on the right hand side i've written everything on the left on the right hand side i've got zinc two plus plus copper okay so there you have it okay so this now would be your net cell reaction now usually they may even ask us about the emf of the cell so all that you simply do you are usually given that reaction or equation okay uh i won't show you how to derive it you just need to know how to use it that's the most important thing right and all that the equation tells us is e cell okay note they always put a standard there remember standard conditions we said uh concentration uh temperature and pressure right so that's going to be e cathode it's always going to be e cathode standard okay minus e anode the e standard of the anode okay so when they say calculate the emf i'm simply going to say all right this is going to be e cathode so which one is my cathode we said it's copper what's my potential that's 0.34 okay minus in this case right so there's the minus there but remember that the anode was already negative so that's minus a negative 0.76 okay and in this case negative times a negative gives us a positive so we've got 0.34 plus 0.76 which will give us 1.10 volts so that's 1.1 volts so that would be the emf of the cell now ladies and gents i want to to to give a warning if you ever calculated this and you get a negative value it means that you've done something incorrectly okay for the galvanic cell just remember that your e cell will always be positive okay right so now there it is we've got our net cell reaction and we've got our um um our our emf okay now i just want to break it down and show you what actually is happening in the cell all right so that you understand it from the perspective in which we started with a cathode and anode so it means in this cell zinc the solid is breaking down or ionizing and forming more zn2 plus ions okay so it means zinc the solid okay which is this guy over here it's breaking down and forming zinc two plus okay zinc two plus okay so there's the zinc two plus ions but now as it does that remember now it obviously now manufactures electrons it becomes zinc two plus because it leaves electrons over here right so now those electrons they are full over here they now start moving through that wire okay so they start moving through the wire over there okay so on this side as these electrons arrive now think about it this guy is transporting electrons and bringing them onto the site now the copper two plus ions are simply saying hey we are positively charged there's an electron over there okay so copper two plus sees electrons so there's copper two plus over there sees the electrons and it attaches itself to that electron and it becomes copper so it means your ions remember this these are in solutions these are not actual you can't actually see them right so the copper ions which are usually blue in color right uh now see electrons and now they go and attach themselves and they form copper over there right now what begins to happen this guy keeps producing zn2 plus remember this equate this reaction doesn't just occur once right keeps occurring all right keeps forming zn2 plus and forming an electron they're forming electrons z and two plus forming electrons this guy over here copper 2 plus right it's now seeing those electrons and are touching itself over there so what happens at this cathode so this cathode keeps forming more copper copper more copper and you'll see it begin to gain mass remember what we said we said at the electro at the cathode the cathode gains mass so this guy would end up gaining mass but what would happen to this guy because now it's slowly shedding off those electrons and it's shedding off those ions in this case this guy will get smaller and smaller in size so in this case you'd see this one becoming smaller in size corroding in a sense and this one gaining mess okay i hope that you're with me right now um just the last part that i just want to show you before i get to the uh net cell reaction so in this case now what we do have is that those copper ions you remember that they they keep they kept on leaving right now what are they leaving behind remember they were not on their own that copper was with the nitrate ions over there so you've got nitrate ions that are all over the sky okay so nitrate ions say hey but now we are lonely because our partners have left so the nitrate ions would tend to go to the um salt bridge and go to neutralize you remember what we said we said it neutralizes excess ions right but here you keep producing lots and lots of zinc uh two plus ions right so thosing two plus ions there are more and more and more of them and now they're in excess so what do they do they go into the salt bridge okay to go and neutralize so that's the function of the salt bridge to neutralize those excess ions ladies and gents i'm not really trying to make this cumbersome but i really want you to understand what is happening in this cell okay so as a result okay we said that uh um now the the copper plus ions ah sorry there's zinc two plus ions now go into that reaction and please i want you to note now they are neutralized over there so we call these uh two plus ions okay or the positive ions we call them cat ions all right um so we call them cat ions right so the cat ions i want you to please note the cat ions always follow the direction of the electrons so the cations will always move in the direction of the electrons and these nitrate ions that we're talking about the lonely parts there okay now simply say hey we are now lonely they go into the salt bridge and they go and neutralize over there and in this case what begins to happen okay so they get neutralized over there so these we call by the way those negative ions we call them um n ions right right so remember on this side we've got cat ions on this side we've got n ions okay right now just the last thing that i want to show you ladies and gents so this reaction do you see that we've got copper two plus there but we didn't have copper two plus in the reaction so we are actually they can actually write this reaction as it's copper sorry zinc plus copper nitrate and i'm gonna give you the name uh of these nitrate ions there why we wrote it in that way okay and then they give that gives us zinc so remember we didn't have zinc but we had zinc nitrate so this gives us zinc nitrate okay so zn no3 now notice once again okay that n is two plus so i'll put a two over there okay plus copper so you can write down this reaction that way now it means in this format we have written it down without the spectator ions what are the spectator ions in this case it's the nitrate ions okay they remain relatively unchanged right so we call them spectators you know like in a soccer match when you go and watch a soccer match you don't participate in the game isn't it right so in this case uh um these guys are just watching they don't participate in the reaction and so we call them spectator ions okay right and by the way this is perfectly okay it's sufficient okay right last thing that i want to show you ladies and gents okay so what i want to show you quickly is we can also write down what we call uh um the standard cell notation okay and how we write down the standard cell notation for the cell we'll simply say the standard cell notation simply says okay you start with the anode so which one is our anode we said zinc is the anode so what happens to zinc it moves from zinc to zn2 plus so it would change from zinc and this simply means change in phase right so it changes phase and it becomes zinc two plus all right and we use this to symbolize the salt bridge so this designates a salt bridge okay right uh sorry it's out of your view there lit a little bit okay so this remember it shows us the change in phase so we know that we are changing in phase so it's moving from solid okay and it goes into accuracy mode right remember we said that zinc is going from solid from being a zinc and it becomes zinc two plus so zinc to zinc two plus there which is aqueous but on the cathode side so we always have the anode on this side right on the cathode side we'll always have so here we started with copper two plus and copper two plus changed to copper so copper two plus which is the aqueous form of it changes phase and what does it become it becomes copper all right so so remember that copper de is solid it's in solid form okay so in this case this is what this reaction would look like now ladies and gents i've already produced a video where i am going through past exam questions on this so you can go and refer to that video to see how i uh tackle more of these questions now in this particular question what in this particular video rather what i wanted to do was just to show you how this cell actually operates and to give you some of the uh you know um you know some of the reactions that take place in the galvanic cell okay and i just want to make a shout out to mohammed all right uh who actually asked me to go through this section okay i hope that you'll enjoy this lesson so i just want to leave it here otherwise from me for now all right i'll see you next time and please just keep working hard ladies and gents and those exams are coming uh please make sure that you ace those exams all right so until next time i'll see you again shop shop