Electrochemistry part 9

追加: 2026-05-12

[00:00:00]last class we read it up to this this much we have done it the last class if you remember it here oxidation takes place because you can see oxidation reaction is taking place so electrons is accumulating here and as a result the electronic current flows from zinc to copper and as you can see this is a positive electrode so the conventional current flows from copper to zinc we can see that clear so here the reduction is taking place I can see here gain of electrons is reduction and loss of electrons is oxidation because now what do you find is that I said you that without the salt bridge this reaction is not possible because the cell is not complete the cell reaction is not complete so what is the function of a solid bridge ready Don first function is not cell bridge it connects the two half-cells necessary Gosnell this is your observation toxin this is a reduction russell's it connects the two half-cells and does it completes the circuit against Allah it connects the two half-cells and it completes the circuit point number one point number two the function of the salt bridges it maintains the electrical neutrality of the cell it maintains the electrical neutrality of the cell that means cell is remaining electrically neutral in nature now this year to understand that how a cell remains electrical you understand see I think you're great the two functions my just what a silly so he what he finds here that sulphate ions get accumulated okay because zinc sulfate but you can say you're three times get deposited now zinc ions in is coming from it is coming from zinc electrode the zinc ions so Z times modified exact here it reacts with the sulfate ions because zinc sulfate will dissociate to give you nothing but Z n 2 plus plus so4 2 - all right so this this zinc will be actually subject to competences in suffix and typically what you find is out that zinc is gonna come negative so this becomes sweating and say slightly positive this particular cell becomes slightly positive clear done no next here what it happens here the sulfate ions accumulate sulfate is gonna come accumulated here how because copper sulfate dissociates to give you Cu two plus plus so4 2 minus so Cu 2 plus gains two electrons to form copper which gets precipitated here at the bottom we can see that as a ready strong Peabody but a sulfate ions gets accumulated so this will become slightly electronegative and this cell becomes likely electro positive so it becomes starts out yes so now the function of the solid which you listen what I say salt which maintains that you can improve yourself so when this becomes slightly electro positive cl- ions comes from here because in the salt bridge what is that KC a wrap ACL or ammonium chloride or potassium nitrate necessary which should get me not electrolyte mix should not react with this to electronic and say to the Restless so what will happen here as the kinetic accumulated listen carefully zinc ions get accumulated as you can see CH here alright so you react see the CL minus and cl- ions come from here to give what I can say zinc chloride so it becomes wanted to tell you neutral it becomes electrically neutral now how CL minus is Lena the serum ensigns know that I have to get to zinc know how it will come see when the two electrons from zinc then zinc loses two electron this electron goes from to Z and it reaches here copper so copper reacts it is to you from the copper and metal atom then what will happen now what do you happen is that the sulphate ions is so core to man the sulphate is something to move the magnet is not need to go that ions is going to move alright now how the ice is going to move potassium ion is going to pull the sulphate ions towards itself listen carefully potassium ion is going to pull the sulphate ions towards itself as a result the charges enter enters through this sonic the charges enters through this and hence it gets it to Kelly neutralized the charges and it enters now the charge the charge has to also pass through this somehow the charging pass through this zinc will pull that particular charge towards itself we charged the negative charges need to pull towards itself there is cl- ions ultimately comes towards this second it becomes what zinc chloride and here your habits the sulfate ions is being pulled by the potassium ion to form potassium sulfate and here the same times is being pulled by cl- ions to form zinc chloride so who is pulling here that is here potassium is willing to surf a tunnel the charging ducks and here who is pulling the same kinds is pulling the clearances charge leaks from here the charges intern believes and hence the circuit gets completed so the circuit not only gets completed already not only the solder bridge helps to what he can say complete the circuit and helps to connects the two hassles but at the same time it maintains an electrically neutral understood how it maintains electrical utility Z times will the chloride ions to form zinc chloride utilized here that potassium and is being pulled by sulphate ions by sulphur dyes and hence it gets neutralized in this way this is a function of the solid region does the reaction goes on alright so this is the what you can say function of the salt bridge and this is your entire working of a galvanic cell because of that now we will study how to represent the cell now see here you can change the electrolyte and the electrode and you can use different different but you can say said you can make it so this is a galvanic cell you can make any other cell you can make look like cell you can make well tax and in any other sense just what you can do is that you have to change the electrode are they don't relate and you you have to what you can see use it now every time it is not possible to draw it in this way and what you can say explain the children it's not possible even in the exam suppose you can give you a question to you do finger I have to write it this way and I will be giving a question will it will he see or you have to answer me nice video I did this when you have to answer me not possible so we have got a representation for it how did we have got a shortcut method to it present this particular cell so hence now I am going to teach you the cell representation how to represent this particular cell correct listen it now I understand so when you are representing a particular cell always the oxidation listen carefully always the oxidation is written oxidation reaction on the left hand side and the reduction reaction is written on the right hand side oxidation means but it that is M / MN + because in oxidation what it happens him let us say n is there and in cement or any matter it uses any electrons to Papua MN + this is an oxidation rate so that's what I read any / MN + means what this is the shortcut way of representing the oxidation reaction which should always rated on the left hand side while by representing a cell left hand side listen carefully oxidation reaction that is either the reaction which is taking place at the eyelets around is written of the left hand side now reduction is or MN + + + E - will give me 1 and this is reduction reaction now it should be written on the right hand side that means MN + 2 and here what do you got m2 MN + c m2 MN + - of electrons and ma + 2 n is how much the gain of electrons so what will you write MN + 2 m this is a general representation I am showing you and in between I put a double slash double slash is not the salt bridge so this is your oxidation part the iron and this is a reduction part that captured so this is the circuit presentation and you have to always write in this manner only always oxidation written on the left hand side reduction is written on the right hand side you can't change it you can change it that you can't change this particular but it for example the galvanic cell what will I do so what are you succeeding certain - to me - gives the red to plus and Cu 2 plus plus 2 e - will be what see you so this is your oxidation of half cell reaction and similar observation half reaction and this is a severe reduction half reaction so how will I represent this particular one I represent in this residence last two plus double slash double SATs this is a Sardar bridge double flash means a solder bridge gifts sorry gives me Cu two plus gives you all this oxidation lag reduction right if you're changing means meaning is going to change how will you know for that purpose internationally according to IUPAC we have adapted this particular thing that whenever we like something on the left hand side the Queen's are writing the oxidation reaction and whether I'll be writing here that means I'm reading the reduction reaction and here also you can write the concentration here suppose if it is one bar we can write blue one belong or it is is 0.5 molar we can write zero point five o'clock we can write here solid or you can write any liquid a of taking or gas you have taken anything everything you can write it down so this is known as cell a representation or the cell notation because of that cell representation of cell notation right the rules what I said oxidation left reduction right in between double slash is next part which alright in this way you represent a particular set this shortcut way of representation now next after that we will understand electrode potential electrode potential so then and when an electrode is put into an electrolyte when an electrode is put in Canada flight three things can happen three things what is that either it can lose electrons that is it can undergo oxidation like zinc you can see it here it loses electrons on it and it undergoes oxidation listen carefully now the second thing it can happen is that it can gain electrons and it can undergo the reduction like in case of copper yourself correct copper is gaining electrons and it is what it can say it is forming copper ironic answer that all right so all the color thing it can happen is that and whose electrons knowledge can gain electrons so what is that type of electrode we call it as null electro null null that means in our theater we can said so there are certain electrode which does not participate in the electrolytic reactions which does not pass of it so they are considered to be as null electrode correct and the potential of that electron dispenser to be s is zero zero potential yes so when I say null electrode means for I said neither oxidation or reduction see if a particular electron either undergoes oxidation or reduction then what will be the potential see what are you be the work that potential is the god what are you putting in a potential potential in physics your circuit it's the amount of work done in bringing a unique positive charge from infinity close of input and ideally what if it does not wait anybody can say oxidation and reduction no nothing so hence yeah it is zero potential we prove it are super very I am going to prove it also and how the null electrode is of zero potential all right so three things can happen when a electrode is dipped into an electrolytic solutions either it can lose electrons at this exhibition or it can gain electrons at this reduction or neither it can lose noid and gain electrons that is neither can peroxidation nor it can undergo reduction that is that particular electrode recently yes okay thank you very much next