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Lecture 17. Electrochemistry Pt. 2.


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Title Lecture 17. Electrochemistry Pt. 2.
Title of Series Chemistry 1C: General Chemistry
Part Number 17
Number of Parts 26
Author Arasasingham, Ramesh D.
License CC Attribution - ShareAlike 3.0 USA:
You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor and the work or content is shared also in adapted form only under the conditions of this license.
DOI 10.5446/19006
Publisher University of California Irvine (UCI)
Release Date 2013
Language English

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Subject Area Chemistry
Abstract UCI Chem 1C General Chemistry (Spring 2013) Lec 17. General Chemistry -- Electrochemistry -- Part 2 Instructor: Ramesh D. Arasasingham, Ph.D. Description: UCI Chem 1C is the third and final quarter of General Chemistry series and covers the following topics: equilibria, aqueous acid-base equilibria, solubility equilibria, oxidation reduction reactions, electrochemistry; kinetics; special topics. Index of Topics: 0:00:00 Balancing Redox Reaction Review 0:14:46 Balancing Redox Reaction in Acidic or Basic Solution 0:19:07 Balancing Redox in Acidic Aqueous Solution 0:23:46 Rules for Balancing in Acidic/Basic Aqueous Solution 0:34:18 Example in Basic Aqueous Solution 0:47:56 Example in Acidic Solution
OK I was going to start does anybody have any questions before I begin all right so you don't remember at the end of class last time we looked at balancing oxidation reduction reactions and I said that if you take a reaction like
the combustion so the 1st example we took last time we looked at reacts with oxygen to give you convent outside and what and in this redox reactions and you can use the usual method of balancing equations where you can look at the number of Adams on the left-hand side and make sure that the number of Adams concern a player surveyed wanted analysis equation you we know that there's 1 company 1 car and if I want a balanced 192 waters on the side and therefore I need 2 0 to cities by looking at the number of patterns of each type on the left-hand side of the balance it out on the right-hand side as well so this is 1 of those examples was pretty straightforward and balance it the way you usually balance equations wants to balance the equation and I'm not going to go through the process with you guys remember that we said This is being oxidized and we said This is being reduced and this is being oxidized and this has to be the reducing agent and if that is being reduced oxygen has to be the oxidizing agent analysis of the oxidation numbers told us that the electrons are transferred this reaction the substance being oxidized loses 8 electrons in the substance being reduced takes up 8 electrons in the form in which balanced equation is written the but I could also there are some examples some the equations of their marriage difficult to balance in the older with they can balance then is by looking at the oxidation numbers and I had a lot of questions from students after class and on this so I will go ahead and work at last example that working-class because we were kind of rash and some of you Wyoming to redo that example and show you how to to figure out how to balance equation so if we write down the reactants we have sodium chloride plus age 2 cancel 4 plus in a note to giving me any aid to hassle for mn C 2 each to bowl and see all too apparent show this is an unbalanced equation and I got to balance it and now this is 1 of the examples where if you would use that the usual method it would be virtually impossible to balance this equation is you have to use oxidation numbers so they the equation at this time then of course you have to sign oxidation numbers so they quickly remember we always assigned oxidation number for 1 that you can always compare 1 atom with 1 that you can't compare the oxidation of 2 Adams with 1 hand understand so that's why women apprentices that put the oxidation number that corresponds to 1 individual atoms and that's what we're going to compared to even know you may have more than 1 the coefficient France represents the number of said there appeared to be a look at some of the images have 1 its once you know the opposition number is plus 1
you know that chloride
has an oxygen negative 1 Indigo sulfuric acid we have to 2 hydrogen any
title it last won since this oxygen on sulfur is to and therefore those you can figure out that so you remember some of the oxidation numbers gives the overall title molecule hydrogen and oxygen forgot the oxygen of sulfurous so you know that this is sits there therefore of these and that would be needed to write so that the sum of all this 0 and the 1 that you don't know at this himself and by using hydrogen and oxygen leaving the oxygen of sulfur OK now we hear each oxygen is negative to those on the oxygen site natives for their therefore the manganese has to be 1 positive 1 now returned to sodium this sodium again we have to so Indians plus 1 solve where once again he knew the announces the this has to class this has a negative data therefore this offer has to be plus 6 therefore oxidants each of which is native to now we hear the maddening there to Chloride so we know this is plus 2 and we have to chloride which is negative ones in water that we have to fast ones and a negative 2 and chlorine and we have to chlorine you tell me which 0 because it's an element in its natural state the reason that so we must sign the oxidation numbers for all the items of all the substances that there's reactants in his products appear now I wanted to our other any 1 of these the undergoing any changes are right and it is clear about that sort of many agencies starts at cost for Costa 2 so that's 1 change we all right and the other change is chloride goes to 0 so those are the 2 changes that we observe everything else remains unchanged all right so which 1 of these is the 1 where the oxidation of amenities so what happens to the oxidation of reminding goes last for 2 plus 2 illegals from cross-border costumed as the oxidation of increased or decreased decrease if the oxygen of a decreases in oxidation or reduction reduction so we know that the manganese is undergoing a reduction it is 1 adamant that it is by how much does it decrease you with opposition members what is the relative change to so that means it's a reduction in a reduction in the pilot was picked up for lost time I picked up the 2nd game so we don't 2 electrons hygiene and so the show that electrons a game-winner put a plus sign in front of to electrons are being picked up bad so we know that when manganese undergoes that transformation it's undergoing a reductions and that 2 electrons being picked up directions None the chlorine and you look at a chlorine in eagles from negative 1 2 0 as the oxidation of increased or decreased increases without additional increases what would that oxidation ahead so that would be the oxidation now you taking 1 Adam it goes from negative 1 2 0 so what is a welcome change 1 ceramic oxidation intellectuals lost so they already have them when it undergoes this change will lose 1 lecture got so when you balance equations remember in oxidation reduction reaction is What is the cardinal rule that you cannot read and that is the number of electrons given all I have to be the number of electrons taken up so to make them the wall I twice as many chlorine atoms undergoing an oxidation so in other words to make it 2 electrodes that picked up the wall To this end and have to multiply this by 2 In a receiver the now 2 electrons or lost to elect undertake up so that means I need to chlorine atoms here that siren did you have to to chlorine atoms member is relative changes 1 calling and one-to-one 1 coordinator so I always have to chlorine atoms here and that means I need to point out on the side but can you see there's another set of chlorine atoms here that don't undergoing change so that the 2 types of of chlorine atoms that there's some chlorine atoms like spectators instead of undergoing change then there are the chlorine atoms that actually are oxidized now the reason that absolutely impossible to balance these kinds of equations is because you don't know what is the ratio of the chlorine atoms that still undergoing change and those items that do when were changed to see that and that's why I had little these kinds of problems you actively look at oxidation numbers to together the number of elections involved in downstairs so if you look at that I have already no I'm on assignment to electrons a loss I can't change the number of manganese iron and steel therefore I cannot change the chlorine atoms have to its here and have to glorious that come from the 1 that undergoes changes so if you total up the number of chlorine atoms have recorded and so I have to hear and to hear that gives 4 sometimes they chlorine atoms on the sites of what I've done I've balanced manganese and iron balanced the according balance species that oxidation and balance species that undergo reduction now I can go back and now I have to just the really to make sure everything else balanced so that he has little back-and-forth full chlorides I I audience but also idioms like over here and say I need to sodium on that side so that it gives me a total force of message about sodium journalists often there to solve its hero the overall you take this offer and I'm here to celebrate the tenants here so harmless offered installing it on the site to for 2 now that balance sulfates I need to make sure that hydrogen I write cycle the here and now I have 4 hydrogen so now I can quickly check with equation is balanced right so this equation is not balanced a page now I can go figure this out by by saying how many students so I have forced audience for students I have for chlorides handful Clerides on the side I have for hydrogen 400 and I have to 1st over here 2 staffers OK never what about oxygen you can see that I have a oxygen plus 2 we 10 oxygen on the side so I of 10 oxygen atoms on the reactants side therefore you can see I plus 2 I have 10 oxygen on the product side so the only thing
left is manganese I have 1 manganese here I have 1 manganese unit considerable both sides the number of adults of each element and balances so that this is a balanced equation now want to balance this we held that the substance being oxidized is an easier out right there you could also say it in the house it's a seal minus that actually oxidizer because it comes as 1 package wouldn't say sodium chloride is oxidized but we know all within sodium fluoride captured the chloride ions that are actually being oxidized again severe after what is being oxidized it acceptable to say NEC out is also acceptable to among on the other hand what is being reduced this is the substance being reduced arrived and severe asked what substances being reduced and you can see and then on to or are you wanted the managers should stay in meant four-plus because the man cat I'm charges for plus are viewed as a mechanism will be metallic manganese and you don't have it manganese here during so you have to say that you just say it's there in full class that would be great but because the oxidation state of that can find a charter that can people plants the now this is oxidized this would be the reducing agent of this is reduced that the the oxidizing agent and overall we know what to do electrons are transferred now that the example you have to analyze it in this way because 1 of the learning outcomes for redox reaction is for you to be able to look at a reaction initially tapped you should aware talent with oxygen reduction reaction if it is oxidation reduction reactions you know you need to know what is being oxidized was being reduced when the oxidizing agent what is a reducing agent in you need to know how many electrons have been transferred OK now this is 1 way of balancing redox reactions OK now this special classes of reactions where it's like a subset so we look at different ways of balancing oxidation reduction reactions as 1 way to look at the questions you can do it by just looking at the Adams and he decided that we created by the army the meeting examples but many other examples of virtually impossible the balance and this would look at the oxidation numbers gave no some said that is where we're looking at balancing redox reactions the end of the this city of the quest for solutions 4 of the 6 8 Quest Solutions can now it's important that you realize that this is a subset and you don't mix up the approach that we to balance these equations with the percentage taken before because sometimes when students come to my office hours and I ask you to show me how figure it out the use a mishmash of both approaches I and use a mishmash of both approaches yeah not getting in way they are the only time you used that approach that eventually right now is it a question actually specifies and tells you balance this inner-city with solution of basic increase emissions because the solution is the center all of you recognize that the solution is acidic what we have is each 83 or class and water and sometimes it's easier for us to just considered as H class in its 2 0 all of you recognize that now that you understand acid-base chemistry at the solution is the city it has ageless science but the reason we don't consider states was signed in water each class does not exist as an entity of its own little combined with water your class and we said candidates steel classes not the complete picture in fact the HVO classes hydrogen bonded to lots of molecules of water and he has expanded structure and so in writing to your class is not an accurate description of pain but regardless but these problems it's convenient to just think of it as a plus or and it it is they say we know the fact that it's basically means that it's got hydroxide and water in here all right so let's say you're given a question where you asked to balance so that balances the following reaction in the city Equus solutions balance the following reaction in a city a quest for solutions OK and that same equation given to you is that the 2 plus but cost plus a manual for minus the requests the venue if the 3 plus request but 1st and then to Class requests so this is the unbalanced equation and when you look at this unbalanced equation you can see that the elements are missing so 1 way to tell Is it leaves you see that about what the the unbalanced equation is missing you misses oxygen and hydrogen are right to build the new see that on the left-hand side who have oxygen inevitable miners on the product side you see any oxygen not so the it announced that it means that that equation is incomplete are right and the reason it's incomplete is what's missing in water and if it's acidic solutions it's water and age plus is missing from that the basic solutions what's missing from that equation is always minus 1 so you have to bring those and when you balance equation that's why this is a special subset all right and you have to keep it separated and you have to look at what you're being asked to do if you're asked just balance equation you can use this method specifies saying bounces equation in city solution of basic was solution that's the only time you can use this approach and you can't you will use his approach where hydrogen and oxygen are missing out on either on both sides on 1 side OK so what would happen if you with that which you have to keep in mind that the show you a sort of a shortcut and it's convenient to remember the past are right suddenly under the table and on 1 side and there's same need on the other side and that are riding a balancing these equations you look for what's missing is 1 oxygen atom is missing then this is what you need to do so let's start with that saying you need a hydrogen and let's say urine acidity Equus solution so there's a city gate was solution and you need a hydrogen to balance equation that hydrogen is missing from this last waste to bring in a hydrogen and then on the other side you put in each class right now it's much easier to do their and you wanted to be more accurate than you would put each or loss on 1 side and H 2 on on the other side and you see that you needed extra hydrogen whether on the product side or you need on reactants sided with HBO plus you on the other side what is the difference between the 2 the net is that it's your Plus has 1 extracted plus this see that an but that's why we will react to it it's acceptable to like this for these you know you can write a plus keeping
in mind that you know that it is really needs dual-class and even that is not an accurate picture of 10 now oxygen what you do it is on the site that you need oxygen you put speech to all and on the other side of the equation you will put L 2 each plan write to you compare the Sudanese title on side you 2 hydrogen on that side so the 202 would cancel each other so the net result is that you have an extra oxygen or I put this sort of battle with 2 heads because depending on whether you want on the product side on the reacted side we can reverse that anyway you want depending on where you want that extra oxygen he 1 of the products I will reverse that you want strictly accurate then you would write this as on 3 h to all on 1 side on the other side you put to H 3 0 plus the net result is that you have an extra oxygen on the side of underlined that extra oxygen because signatory Oxygen steer them into oxygen and that side but it's easier to stick to that so that are in Aceh the ink was solution not good are in this state the it was solution then you need a hydrogen they want to do it on the side that you want that extra hydrogen from water and on the other side you put forward to minus 2 can you see on this side 1 oxygen as 1 oxygen the site but we get to hydrogen over here there's only 1 hydrogen so the net result is that you have extra hydrogen on the site if you want to oxygen and undecided 1 oxygen there which occurred 2 0 which miners and on the other side you put into also can erase you have to oxygen on the side you have 1 oxygen into the net result is that you have an extra oxygen are so this thing this table handy and you do a couple of examples and depending on what the solution of basic solution now you can solve this by bringing this example sold you did this example you start 1st to balance his dark 1st by writing to reactions so you have displayed equation that's given to you indeed to have reacted cement where you are right half reaction you know I'm supposed to I'm 3 busses to post goes to this this is the other half reaction are right so that many to have reactions I would say if the 2 players goes to the 53 plus and Aminul for miners goes to amend two-plus that so the 1st step is for all these kinds of problems you 1st with them to have reactions are 2nd now you balance ball at the end of this ride using H 2 h last or which miners as needed OK so if it's basic solution is to use all its minus in water if it's acidic solution use age plus and water seller now and go back to the same equation and it's been a balance all the adults so here I have I made headlines in the hands the outsiders to bring water into this because there's no oxygen hydrogen in that equation however in the 2nd 1 I have 1 manganese I have 1 manganese but you can see I'm for oxygen Our right so that means about what this I need to bring in 4 oxygen OK so it might turn to my table remember in this table it violates the acidic solution so somewhere remember this is necessary solution the questions is balanced this inner-city was solution inner-city cake was solution if I meanwhile oxygen and I need to bring water air and on the other side with 2 At last holiday often used there I've forgotten about the size standard for oxygen on the side so how many waters went bringing underside for some of them for each to 0 in on the other side of every month of water and to add to its plus harmony each pluses record here it passed to see so by
bringing in H 2 0 an age plus now I'm able to balance the oxygen a check 1 9 1 0 I a hydrogen is 4 times to hydrogen so I 1 manganese 1 man in his idea for oxygen and I have for oxygen and so I found of patterns a no the 3rd staff is now members said whenever you balance equations there are 2 things that you need to look for 1 of those you have to have an imbalance in what is the next thing I keep reminding me this quarter was the other thing that we need to member charged Celtic charged you can created history charge or so whatever charge you have on the left-hand side has to equal the charge on the right-hand side so now we have to balance the charges N both have reactions using I right so let's go remedies that have reaction saying have reacted you have to show of electrons being lost and electrons being gay all right so if I would take the first-half reaction anyone in the balance charge because he's a redox reactions with bring electrons to balance charts the case elicited this this is going from Lyon to last 2 iron three-plus now I need to balance charged by the electrons and so that 1 electron on this side what is the overall charge here last year and this is the last and as a minus-1 see overall title on that side would be passed to as well are right now all I have is electrons invited electrons and decided that won election on this site with overall total amount to be plus 1 or a solid muscle in on this side and plus 3 on that side that's not an e-mail the only way that can balance charged here is to put a lid on this side are right and I would have balanced charged now let's go to the other 1 the other half reaction was 80 plus plus in miners gives me mn 2 plus plus 4 each to bowl right similar to the charges on this side I have a plus and minus 1 so what is a world charged here plus other university that I a class last coming from the hydrogen and have a minus 1 so I have lost 7 on this side I have plus to all right so all I have available to me I electrons and I need to make them that the charges balance OK so can you see that I if I put more electrons on this side this will go down even more in the plus 100 report electronic on the side of the Class 1 that's not going to help me ,comma electrons do I need to put on this site so that these 2 balance each other fight sequence he 5 electrons are you so another in moving electrons on this side than in the letter law on the side because you know that have been picked up 2nd ever see that this is the oxidation half reaction and this is the reduction half reaction now the 4th step is a cardinal rule member of the redox chemistry What is the cardinal rule the number of electrons given not have to pull the number of leptin sticking up in the 1st reaction 1 electron is taken up in the 2nd 1 5 electrons a given off so the net outcome is that you have to have 5 electrons lost in 5 elections game so how highlighted by electrons on this side I multiply reading by the coefficient 5 are right said now and the 2 reactions OK keeping in mind that's the electrons that the number of electrons must equal the number of electrons gain right so that means I know that I have to multiply this by 5 all right in order to balance said so when I will have 5 if the 2 class giving me 5 if each week last plus 5 electric centers and multiply everything in the top equation by the confession 5 and then at the bottom of the have 5 electrons plus 8 each class the plus for minors giving me mn to Class 1st 4 it's too take so now I can add these 2 regions together right and when I addresses to equations together you can see me that's the number of electrons lost the number electron gain will cancel each other out so would end up with is inspired 52 plastered all the reactions on the reactants I plus 8 each plus plus a manual for minors would give me 5 if the 3 plus plus mn to plus plus for H 2 0 alright so now look at this equated to Kanye reduces further sometimes you can reduce everything To the lowest whole numbers or I can reduce the coefficients to any of the lower number no right to know the last step is for me to quickly check with this equation is balanced obtained so once again we start with I have 5 times 5 times I have to tide against 4 times to the hydrogen 1 manganese 1 manganese I have for oxygen on the side I have forgotten that size I have Adam balance again next step is to have charged balance that's a quick way to check with the equations balance so I have 5 times to his lieutenant lost I have a policy that is the 18 last and then minus ones out what is the total charge on side plus 17 are right now as again in my balance should have the same time site as well 5 times 3 give me 15 plus plus 2 gives me 17 plus all right I know that my bounce the charges and the sites this equation is balanced OK and I know from them that that's species being oxidized is the species being reduced the 704 -minus because member that this comes from the production have reaction this comes from the oxidation have reaction if this is oxidized this would be the reducing agent it this is reduced this would be the oxidizing agent and overall I know 5 electrons transfer saying this reaction even know when you look at the balance equation you can't tell how reluctant to being transferred because the balance equation does not reveal that to you by going to his analysis now you know that in this reaction 5 electrons have been transferred from the iron to the magazines in an awful minus alright no another exam but this time I will be looking for example where we have this solution you know for the 1st example of stepwise now I can do it all in 1 step all right because you know at the same time you can just do at all of these steps you know it just a single step is soliciting a 2nd example and let's say you're asked to balance was fatally ill going to there's to minus 0 z and to to minors plot Mercury and that's saying that we are in the same inquests solution now is a clear and everybody that using this approach it has to be specified that urinate was solutions you can just use this willy-nilly just because they given you to reactants into products are right you know you can only use it for for these kinds of problems where you can see that oxygen is missing or hundreds of
missing or you told that and basically was solutions some level the 1st but this is just what limited to half reaction so we know this year of zinc on In this have reaction you have to have musings on both sides the other half reaction would be the Geo I'm going to right so the 1st step is to splitting into 2 half reaction the next restricted for use with the need to have the action actions now I do the 2nd step is well and that's so now I have to bring in water any lust for water and hydroxide so now when basic solutions that we need hydrogen you'd lose their you need oxygen you bring into which minus each to all states unless get that I have 1 zinc ones there undecided to oxygen is therefore finally to bring into oxygen is on their side and a member of your basic solution you want 1 oxygen you have to always so I to oxidants Hollywood's minus to forward to minors and on the other side of the reaction I need to put to wage to lock Simon applied for which minus undecided and put to each to on that side the net result is that I added for extra oxygen and site to balance the equation no less quickly checked 1 zinc 1 thing I have to oxygen to oxygen for officers and besides I have for the side I have 2 times to 4 hydrogen as I have for my all right so whatever that is and balanced in hydroxide because in basic solution they want to do and that's what you charge balance right so that all of it all at once so that would charge balance here I have full minus on this side I have to remind on this site all right so how would have downstairs see I electron survived put more electrons on this side this fall minus will become 5 minus that somebody help me so but I bring into electrons here there is now a full minus undecided as to minors and this 2 miners were uniform 1 now look have reaction electrons being lost or electrons being gay lost again because producing electrons selections on the product side is producing electrons and therefore collected on the product side electrons are lost and therefore this would be the oxidation right now on the other side let's go to the I 1 Mercury 1 Mercury I have won a lot on the sites I have to bring 1 extra oxygen undecided and basic solution assignment was to forge minus there and H 2 on this site are right similar to this day 1 my 3 1 2 oxygen to oxygen to hydrogen to hydrogen cyanide balanced case knowing would charge balance the charge balance would be if the electrons being produced here you know electrons he'd be picked up on the site so you know the next up is never straightforward letter that this I have to minus on this side I have neutral neutral so how electrons doing to bring it to sell then we are now electrons on the reactants identities electrons of being picked up sales this is like trying to gain and this would be the reduction right and so now I make sure the number of electrons given not equal the number of electrons in this case histories it's like it's much easier you can see that electrons and given enough to elect undertaken up so I don't have to mount a light these have reactions and to knowledge abuse at him arrange so that now the 2 electrons given in the 2 electrons taken out counts each other out to buy and use to equations together when I end up with for which miners closing plus water plus will give me zinc Louisiana 2 to minus plus 2 H 2 0 plus 8 G plus 2 which might solid added all the reacted to the reactants site in and all the products on the product side now look at that as is some common things on both sides you can see there's water in here and as to water there 10 so it might take is water under the products I didn't see or if I cancel out 1 molecule of water and decided I can get 1 like on this side in 1 month on that side so I have 1 water molecule that I have for which miners on side and I have to minus on this side so revised take this other end up where you can see that this will become too and this will become 1 right solid that this Council common things on the side and my reaction now comes down to 2 or which miners was plus the GAO what do you mean 1st waters thinking right now final test is 1 finally had to confirm whether you have made callous mistakes along the way and on the way to check if they created balanced what does it have to meet there 2 conditions sesame Adams was melons and charges and stuff so quickly go to that desire to oxygen is on the side I have to just 1 3 oxygen is on the side I have to close 1 3 oxygen I have 2 hydrogen I have to hydrogen I have 1 zinc 1 and 1 Mercury 1 Maria overall charge on this site is negative to 4 underside is negative I know this equation is balanced I know you guys want to practice this so that you don't make all sort of stupid mistake that people make when they haven't practiced enough so I'm going to do 1 really fast regimented to more examples and will go through this past because that's the sort of speed at which I'm really be to guilders this OK if you had adequate practice again so let's take this and I wanted to take 2 examples where you might see a curveball and I want to make sure that not thrown off OK so divide takes over plus CNN minus 8 quarters plus 0 2 against giving me see and twice minus requests and let's say you're told that this is in basic solution right so the 1st step is displayed in the to have reactions are right now since 1 of the products is investor has silver and cyanide can you see that 1 Have reaction has to be this all right because if you're going to balance it if you have both of these together we need silver and cyanide together in 1 half reaction so what am I left wing only 2 and so on understood that like irate because when we balance will figure out which come on that side of so don't get thrown off like the 1st 2 examples we saw was very played up to have reactions because you had 1 reacted 1 product ever matched up in another reaction on the part of the matchup here you don't have the matter but that's OK right now where solutions so let's start doing and that's 1 silver and 1 silver homicide and on the side to side to sign it so my hands advanced I don't have really hydroxide and have been water because that reactant doesn't have oxygen hydrogen OK the next step in this time around I have to remind us on this side I have minus 1 on this side Solheim electrons do I need to bring in 1 the electrons are lost so this has to be oxidation the now as good as this 1 we have oxygen level the solution if you want a balance oxygen when the basic solution hydroxide you have to bring in there 2 of the best you need to oxygen we have to bring in more minus and on the other side to each too well just remember this table you need oxygen to Lourdes minus water on the inside
of now let's quickly checked I have for oxygen for oxygen I have for hydrogen for hydrogen inside and that's knowing it would charge Valentine line of electrons have gone site because this is the opposition this has to be the reduction so I have 4 minus on besides harmony electrons do I need to put in over here for electrons because everything else is neutral OK so now when I and we know that this is the game so for this is the reduction right now I have 1 electron undecided for electrons on the side so waterway need to do multiplied by 4 so that the number of electrons given not equal the number of electrons taking up a case of electrons to give enough for electrons and taken out I to add these so I have for so where plus 8 she and minus plus 2 H 2 0 1st all to giving me In G C N twice -minus plus for but for which minus OK now I hope checking along with me to make sure that transferring anything crackers set for a G 8 Sione minors and for that and over here and to which 2 0 0 2 4 8 miners case now look at this and seeking a cancel of any hydroxide the their common hydroxyl is on this side of the common I don't think that you know or want to know this hydroxide is water is no more attractive than the site now see what you can reduce the coefficients any further there's 1 here so I can already with this is for a tube is only 1 oxygen so I can reacting further so that means that this is all I can do no I need to make sure that is actually about so I have 8 silvers and is for silver for silver 8 Sinai times stew 8 cyanide they I have 2 times to 4 hydrogen I have for hydrogen so I have to oxygen plus 2 of this for oxygen so I have for oxygen no I need to do a charge bounce right so overall I have minus the undersigned neutral neutral neutral 8 -minus I have 4 4 times this season for minus plus 4 miners I have negatively on the side so I know the reason is that the last and is now having looked at it as you know what's being oxidized here it's silver can see what's being oxidized is still what's being reduced his oxygen or and this is being oxidized this would be the reducing agent this would be the oxidizing agent and how many electrons and transferred in this reaction for electrons are transferred in the you have to tie you you should be able to rationalize the redox reactions to the build forever ,comma electrons are being transferred OK 1 last example again something that you made and I don't want to get thrown off you see some of these types of questions and the next 1 is quickly we can go to let's say we have the odd to going to be our with 3 minus plus the AA-minus and let's say this is an acidic solution all right so now let's look at the festival in 1 reactant alright it gives you more than the 0 3 miners in all right so that means that to balance there and that that and announced a 2nd hard and indeed Brolin as well so what this means this is unbalanced doesn't mean that you just have 1 molecule of to you have lots of molecules of the to sold some of them I would be oxidized and some of them I would be reduced so this is a unique where the saying react and part of it is oxidized and part of it is reduced to a case and so don't get thrown off you just have 1 reactor and that several minutes this problem and that is you have to use balls OK it's analogous to an ad in to Romans I need to roaming not 2 times 3 gives me 6 oxygen inviting 6 oxidants exulted side I 6 h to all and 12 speech but if you need oxygen in acidic solution deeper waters and to wage plus separate 6 waters because I 6 oxidants 2 times 3 6 and I had 12 each plus inside the 12 each plots so quickly checked to Brahmins to Roman 2 times 6 oxygen 6 oxygen 1206 to 12 heightens our right now good charge balance on this side I have 0 charge on this side I have to -minus and I have 12 8 plus so overall What is the charge besides I have plus 10 so how do I make this the sale all right so what would you do if I put at 10 electrons on this side and had a 10 -minus and 10 lost best-of how we can see that it might pretend electrons on this side since this is 0 10 loss 10 miners will 0 retired from sites are right that figure out where to put electrons and you can see that putting electrons on the site is not going to help you balance charging that being on the side of so this would be the oxidation notice that this I have br to give me to would be our minds sold and balanced now I'm charge balance alright invited charge balance I have 0 charge underside to minus 2nd you see that been to electrons there this would be the reduction OK now if I haven't had a anymore and make sure the number of electrons given off equal the number of electrons taken up what do I have to do on this side multiplied by 5 right now I wouldn't have him up and down with 6 H 2 0 plus the yacht you plus 5 the artillery multiply this by 5 9 go back to this Disney too the article 3 miners plus 12 h plus plus 5 times to give me 10 the minus looking now ask yourself what can I do anything to store and refined this equation can I 1 Romania unified remains there are right so that they can say 6 H 2 people plus 6 B 2 would give me to be our own 3 miners plus 12 h plus plus 10 young minds now let's see what you can cancel out incumbent on both sides can you there's nothing to cancel out attended use this occasion further heresy that actually by the whole thing like to survive everything by 2 enough with 3 H 2 0 plus 3 B R 2 gives me 3 miners must talk 6 each class was fired minus right and and then you can check the charge balance your child and this this is negative 1 misses six-plus triggered by it's 0 charge on the site now the last thing I need to know is we are too is oxidized the R 2 is reduced or I admit this is oxidized this would be the reducing agent if this is really used this is the oxidizing agent ,comma electrons are being transferred to remember their 10 electrons transferred here but I divided everything to so 5 electron transfer so that means and this vast equation 5 electrons are transferred you see that when he divided the whole equation by 2 to the loss coefficients to divide the number of electrons fight that is this
reactions 5 electrons being transferred from
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