to watch these important lessons subscribe to DP education's YouTube channel right now click on the Bell icon to stay updated on the latest lessons Sri Lanka's largest free online school DP education hello my dear students welcome to today's lesson today I am going to discuss with y'all electrochemistry this is the 12th lesson of your grade level science textbook and it is a chemistry lesson so in previous lessons you all have studied about electricity you all know what electricity is it is the flow of charges so that gives rise to an electric current or familiar with that then your family with chemical reactions also now different types of chemical reactions how they occur how reactants are converted to products all that is familiar to you now in this lesson since it is electrochemistry we will try to understand the relationship between a chemical reaction and electricity or electricity and how a chemical reaction can be induced by electricity so that is the lesson here with that introduction students I will move on to the next slide where we look at the contents of this particular lesson electrochemistry now in this we will be first discussing electrochemical cells now you are familiar with cells dry cells that we use for different circuits in your household also you have the dry cells the normal batteries now these are a type of electrochemical cells so here we will try to understand how an electrochemical cell functions and how electricity is generated by a chemical reaction then the second topic is electrolysis or electrolysis Now by passing electric current if you can separate a complex component into more simpler components then that particular process will be understood as electrolysis now this has to be a process that doesn't occur spontaneously normally at room temperature you can't make it happen but by passing electricity you can make that happen so those are types of reactions that are discussed under electrolysis then we have corrosion of metals your familiar with that also now in the lab we have magnesium strips now when you keep it exposed to air you all know there is the magnesium oxide layer forming on it same way rusting of iron now all those come under corrosion of metals so we will be discussing that as well electrochemical cells electrolysis and corrosion of metals so those are the topics that are going to be discussed under this lesson the way that introduction students I will move on to the lesson so first we will discuss what electrochemical cells are look at these pictures first now most of these are familiar to your y'all have either used it or have it at home at least you all know about all these devices a toy car powered by batteries the remote control cars now here you can see this is the toy car the remote control and this is the power pack that you get with the toika either both to charge the car as well as the power pack so there of course you would have seen now this is connected to the car and when you plug it in the car gets charged at the same time for the remote control you will need to use batteries and in that you would have seen these two types of batteries normally we put the dry cells into the remote control whereas a type of cell like this is used in the toy car that is a rechargeable battery so these two types of batteries a normal battery and a rechargeable battery both are type of electrochemical cells the dry cells the batteries are electrochemical cells then an electric torch now you all are familiar with different sizes of batteries a size double a size Triple A size like that you have seen different sizes then we have 1.5 volt batteries nine volt batteries like that you have seen different sizes shapes and the different voltages that are produced by those batteries so here electric torch uses batteries then mobile phones we do have mobile phones again different sizes and shapes there are some batteries that can be taken out from the mobile phone but the most modern ones you cannot remove the casing and take out the battery but there is a dry cell in it then you have the calculators now here you can see this is a solar powered calculator here it's a solar cell automatically it generates electricity in the presence of Life at the same time there will be batteries inside so a calculator uses batteries then a computer now we use the computer the laptops normally there are non-batteries then you can recharge it when the battery is low you recharge it connected to the power source and you get it recharge so there are also there is a battery being used in addition to this there are so many other equipments devices or materials that use batteries even a wristwatch so many things so all those use dry cells or batteries and these batteries are electrochemical cells because inside the battery there is a chemical reaction taking place that generates electricity so they are all electrochemical cells now if we look at the introduction in our everyday life we frequently use equipment powered by domestic electricity one form is domestic electricity as well as appliances operated by electrochemical cells or batteries so like I told you we charge the laptop we charge the toy cars then we use the domestic electricity you have learned about electricity also so then you are very familiar with that otherwise we use electrochemical cells or batteries toy cars electric torches calculators computers and mobile phones are a few examples for equipment that are powered by electrochemical cells so those are a few equipment you can think about many more equipments that you use at home so that is just the introduction to these lessons again I will move on to the next slide the electrochemical cells or batteries used in the examples given above are small in size now first look at all these batteries like I told you all now this is a 9 volt battery flat and a rectangular shape there are many like that then you have seen this cylindrical shape batteries that also you get in different sizes like I told you all the a double a triple A like that you have different sizes here you can see those then here also somewhat different shapes cylindrical but like you know it's a the surface is not very smooth then we have all these small batteries which are button like batteries very tiny round small cells which you normally put into use for wrist Watchers and devices appliances like that so you get batteries of different shapes and different sizes here it is a pack of batteries also like that also you can get now these are usually small and usually they are just individual batteries with the positive and negative terminal Just One battery now this is for small devices but if you take a motor vehicle a car when they also use batteries now here you can see this is a battery of a car a vehicle battery now that is a large battery which consists of more than one batteries combined together and they are all connected in a series manner we have discussed this with electricity lesson also so that the potential difference gets added up so they provide a higher potential difference so this is a large battery which is made up of more than one or several batteries or electrochemical cells so you have to keep that in mind you can use the batteries or electrochemical cells individually or you can combine them together at that instance or you can have a bad trivia if they have been already combined together I'm sure you all can understand that so here you can see a battery used to start a car is large in size such a battery is a collection of several electrochemical cells so here you have different sizes and shapes now this is one and that is another point just for you all to recall what you already know because you are using batteries in your day-to-day life so your familiar with small batteries and large batteries so that is Again part of the introduction we are yet to go into the lesson where we really discuss how battery produces electricity from chemical reactions so for that I'll move on to the next slide so uh to understand the function of a battery or a dry cell or an electrochemical cell first we need to understand what happens when you make two reactants to react and from there what happens when chemical energy is converted to electric energy or how that happens now for us to have a battery we need to draw out current from the battery so they are electric energy has to be given up but those are chemicals that give out the electric energy so there has to be an energy conversion from chemical energy to electric energy that is what happens in a dry cell or an electrochemical cell so the chemical energy stored in the chemicals they contain is converted to electrical energy so here energy conversion is from chemical energy to electrical energy now you all know students in a battery there are two terminals the positive terminal and the negative terminal now these terminals are actually known as electrodes in electrochemical cells so we will first try to understand what happens at those two terminals so to do that we will look at this activity now here activities to study the reactions occurring in electrochemical cells and the action of those cells so to do that we need these materials here you can see we need a beaker then we need sulfuric acid sulfuric acid and that also dilute sulfuric acid so now you're familiar with acids and how they act in a solution and also your family with dilute and concentrated acid so you all know sulfuric acid is a strong acid and it dissociates completely as well as we need to take the dilute solution of sulfuric acid then we need a zinc plate zinc plate or zinc strip a piece of zinc metal or even a zinc Rod so mainly we need Z so we need a beaker we need sulfuric acid and a piece of C this is what we will do we will take a small amount of sulfuric acid into the beaker and then into that you will insert the zinc and then you need to observe what happens so that's a simple activity I will discuss the method in the next slide first so the method is this this is what we are going to do we have the beaker here so we have the beaker inside the beaker we take the dilute sulfuric acid sulfuric acid and to that we insert the zinc mat so this is the setup for the activity you have the beaker in that dilute sulfuric acid and then you insert the Z and You observe what happens there add dilute sulfuric acid so here you have to remember it has to be dilute sulfuric acid to the small Beaker place a strip of zinc metal sheet in the beaker so it is a zinc strip of like I said a piece of zinc but there it doesn't have shouldn't be a crunched piece it has to be somewhat long and you know where you can observe part of it has to be within the solution the rust has to be outside so like that it has to be somewhat long so that is why we use a strip of zinc metal sheet in the beaker so that a part of it dips in the sulfuric acid solution as shown in the figure not the full thing that normally earlier when we used to observe reactions we used to put the metal into acid but here we need to have part of the metal outside part of it inside so that is why it has to be either a strip or a rod or a plate we all know the difference right so then you need to record the observation a very simple activity to understand what happens in an electrochemical cell so let's go to the lab and do this activity now okay students so now we'll try to understand what happens in an electrochemical set so as we discussed we all know there is a chemical reaction taking place in a cell that leads to the production of electricity so that is why we call them as electrochemical cells so in electrochemical cells there are two terminals the positive and negative Terminals and they are referred to as electrodes the positive and negative electrode when we look at the function of a cell so to understand that first we will do the simple activity where we have a metal that is zinc metal here you can see this is a zinc metal and here I have sulfuric acid so you're familiar with acids sulfuric acid is a concentrated acid so in the solution it dissociates to form h plus ions and sulfate ions and zinc is a metal so if we put this metal strip that is zinc strip into sulfuric acid you'll have to observe what happens under the solution can you all see the evolving of gas bubbles the gas bubbles are liberated around the metal strip you can see that even if I rotate you will be able to see the gas bubbles here you can see so this is how an electrode functions now like I said sulfuric acid dissociates to form h plus ions and sulfate at the same time now zinc is a metal that has the positive nucleus and the negative electrons you all know in a metal the electrons are free so when zinc is put into sulfuric acid what happens hydrogen gas is liberated that is what you see here around the zinc metal you can see the hydrogen gas so that is because h plus ions from sulfuric acid take up electrons from the zinc metal and then they get converted to hydrogen gas at the same time can you all observe the zinc method you will not see a color change but you can see the zinc metal becoming more clear if you compare the top part of the metal and the bottom part of the metal you will see a difference India color the bottom which is in under the solution becomes more shinier that is because the zinc plate or the zinc metal dissolves so here zinc is dissolving and hydrogen gas is being able so those are the changes taking place in this particular system and this system where we put a metal into an acid is known as an electrode so this is a zinc electrode okay so that so you saw what happens when we dip a zinc plate in diluted sulfuric acid what happened there you were able to see the zinc plate dissolve or react with sulfuric acid there you saw the zinc plate dissolving and you were able to see gas bubbles evolving liberation of gas bubbles those were the observations that we got so here you saw the zinc plate or sheet dissolves then gas bubbles evolve Nia the zinc sheet so those were the observations and also if you let it to react for a long time if the amount of acid and the zinc is high then of course if you feel the beaker you will know there is a certain amount of heat generated the beaker will become hot because you all know reaction of a metal with an acid is an exothermic reaction you're familiar with those types of reactions also the chemical reaction where there is heat evolved during the reaction because the Heat or the energy heat energy contained in the reactants is more and the energy of the products is less because of that heat is released during the reaction so therefore the beak also will be warm that also you can feel but that was not our concern in this particular activity these were the important observations for us now why does this happen to understand that if we try to understand the reason for this this is what happens now if you take dilute sulfuric acid now like I said how do we write this we use the you can use the physical state normally your familiar with that also we write the physical state within brackets now this is dilute sulfuric acid that means it is an aqueous solution sulfuric acid dissolved in water aqueous solution so that is what I have indicated here now you all know dilute sulfuric acid is a strong acid what is a strong acid a substance acidic substance that completely dissociates in the solution so they are what happens when you take h2so4 aqueous in the solution it completely dissociates and forms h plus ions and sulfate ions so42 minus aqueous so both are also in the solution State h2so4 dissociates completely and forms h plus science and sulfate ions if you balance it to h plus so this is complete dissociation foreign dissociation now at the same time when you Place zinc in sulfuric acid what happens there you all know h2so4 this is a reaction that is familiar to your zinc plus h2so4 it gives rise to seeing sulfate plus H2 gas this is the reaction that you are familiar with now in this here zinc is in the metal state but here zinc is in the zinc two plus stay that is what you need to understand now this particular zinc is in the zinc to plastic that is why it iso42 minus so zinc is two plus so in this reaction what has happened to zinc now zinc was in the metal form I'll use a different color just for you all to understand now zinc is a metal solid so we indicate the state of zinc as solid and this zinc becomes Z din 2 plus ayat so for metal an atom to become a positive ion or a cation what should happen electron should be removed from this particular zinc so from zinc electrons are lost and because of that they become Z din 2 plus ions causing 2 plus ions and here this will be in the aqueous State now zinc is the solid zinc reacts the O2 acid and becomes zinc two plus ions by losing two electrons and the zinc two plus ions cannot remain in the meta they go into the solution so that is why this becomes aqueous and because they go into the solution only you see the zinc plate dissolving so this is why we say see the zinc plate dissolves or zinc sheet dissolves dissolves because the solid goes into the aqueous State as ayat and venous species now these are new terms that you all have to understand we'll be discussing these terms throughout the lesson been a species now zinc becomes in Plus losing two electrons so zinc is a species that is losing two electrons when a species loses electrons we call that reaction as an oxidation reaction you have to remember all these terms now this is known as an oxidation reaction oxidation reaction oxidation reaction means a species loses electrons so zinc is the species it is losing electrons and normally all know when you write a chemical reaction or a change we always use plus so all those ink is losing we write the electrons in the product side having a plaster zinc two plus aqueous plus two electron is that clear so as you put the zinc metal into dilute sulfuric acid zinc will get oxidized that means zinc solid will be comes into plus aqueous ions losing two electrons that is the meaning of an oxidation reaction zinc is getting oxidized so what happens there now if you take the system this is the beaker containing the acid and the zinc metal now in this foreign and from here Benzene closest electrons it will go into solution as zinc 2 plus so where do those electrons go they remain in this zinc sheet so zinc loses electrons the zinc solid losses electrons and zinc two plus ions go into the solution at the same time electrons remain on the zinc sheet so electrons are negative charges here these are negative charges negative charges now we saw sulfuric acid has already dissociated now from sulfuric acid we have h plus ions now h plus ions are positive charges so what happens to these charges the positively charge h plus gets attracted to the negatively charged electrons so h plus goes towards the zinc sheet and there what happens is h plus science now they are again in the aqueous state they take up electrons to form H2 gas now here to balance these since there are two hydrogens you need two h plus ions they need to take up two electrons so two h plus a equals takes up two electrons and forms H2 gas now can y'all understand the changes we put the zinc metal into dilute sulfuric acid already the dilute sulfuric acid it's dissociated into h plus ions and sulfate ions so as you put the zinc metal zinc reacts getting oxidized and forming z102 plus height so they are the electrons are left behind on the zinc metal and these h plus ions get attracted to the negatively charged electrons and they take up electrons and become H2 gas so here h plus is taking up electrons when a species takes up electrons we call that as a reduction reaction now this is oxidation this is reduction again I'll use another color a reduction reaction that is a species taking up up electrons is that okay student so two types of reactions occur one species loses electrons that is zinc that is oxidation at the same time another species takes up electrons that is reduction both of those take place so charges are moving electrons are being lost and gay now this is happening in one metal dipped in a dilute sulfuric acid solution if we can make this to happen through an external circuit now if we can have two such systems and if we can make the electrons to flow through the external circuit or an external conductor then we can make electricity to flow that is how an electrochemical cell will function so in this one metal deep thinner acid solution one metal deep tin and acid solution is usually known as an electrode one electrode but for electrons to flow through the external circuit or the external conductor we need to have two electrodes so when you have two electrodes electricity can be generated that is when we have an electrochemical cell so this is the initial part where you understand what happens when you put a metal into acid so after that we will be discussing electrochemical cells so although I have explained all these ones I'll be again explaining it to you all with the reactions in order so this is what happens before I go to the next slide I'll quickly go back and again we will see what happens now during the activity you were able to see the zinc plate dissolve and gas bubbles evolve near the zinc sheet so the reason for that is this you know dilute sulfuric acid is a strong acid so because of that in the undergoes complete dissociation and these are the products h2so for aqueous becomes 2 h plus a equals nso42 minus aqueous you're familiar with all the physical States is for solid Alpha liquid G for gas and AQ for aqueous Solutions so after that happens when you put zinc into sulfuric acid he also we can write the state now he also we can put zinc solid and h2so4 aqueous he also this will be zinc sulfate aqueous and hydrogen gas so always remember students the modern method of writing the physical state of a reactant and products is to write them along with the reactants and products within brackets you don't write it as subscript you have to write it along with the components so zinc solid with h2so4 equals gives rise to zinc sulfate equals plus H2 gas if you include the physical States so here this is what happened saying solid becomes into plus aqueous by losing electrons and that particular reaction is known as an oxidation so here we can say zinc gets oxidized so because of that the zinc solid becomes into plus aqueous that is what we see yes the zinc sheet dissolving dissolving of Z they when you put zinc into dilute sulfuric acid zinc close as electrons and goes into the solution as zinc two plus ions at the same time the electrons remain on the zinc sheet itself and the h plus ions that came from sulfuric acid get attracted to the electrons so they are they go near the zinc plate and there they take up electrons and become H2 gas so when a species takes up electrons it is known as reduction so h plus equals to h plus aqueous takes up electrons and they become H2 gas this is a reduction reaction and in the student now the two reactions that we wrote you can see these two reactions zinc solid becoming zinc two plus losing electrons that is a an oxidation reaction and two h plus a equals taking up electrons and forming H2 gas one thing you have to notice we don't put any physical States for electrons because electrons are subatomic particles so you don't write physical States for electrons you have to remember that and also these two are different from the reactions you have been writing so far in all the reactions you had the reactants products you never had electrons or charges in there this is the first time we are using these types of reactions where you have charges h plus two electrons here zinc two plus two electrons so when you write an equation where you have electrons and charges we call those reactions or equations as half equations or half reaction because this is part of the reaction this is part of the reaction you all know the complete reaction but zinc with sulfuric acid gives rise to zinc sulfate nh2 that is the complete reaction so here we have half reaction and these equations are known as half ionic equations so you have to remember that also now both these reactions zinc solid giving rise to zinc to plus aqueous losing two electrons and two h plus aqueous taking up two electrons to give H2 gas both these are half reactions and therefore the these equations are known as half ionic equation so here students I'm doing it once here and starting from the next slide I'll be repeating all these reactions because this is the first time Yola using half reactions or half ionic equations and you are trying to understand the concept of oxidation and reduction that is why I'll be repeating these again as well so there are two half reactions if you add them together this is one this is two if you add 1 and 2. here when you add always you have to look at the number of electrons now here two electrons here two electrons then of course no problem otherwise you have to make sure that the number of electrons are equal so here you can directly add them together when you add them together zinc solid Plus 2 h plus aqueous plus two electrons give rise to z n 2 plus aqueous plus H2 gas plus 2 electrons you can compare now zinc solid plus 2 h plus aqueous plus two electrons and on this side product side you have zinc two plus aqueous you have H2 gas and again you have two electrons so in this we have electrons in the reactant side electrons in the redoxide and both are equal so because of that you can cancel off the electrons and when you cancel them off and if you write the remaining equation you will get zinc solid plus 2 h plus a equals giving rise to zinc 2 plus a equals plus [Music] H2 gas that is a reaction and in this already there is sulfate ion in the solution why we got this H2 h plus ions from sulfuric acid so they have a sulfate ions so to both sides because the sulfate ion does not undergo any change it remains in the solution as it is so you can add sulfate ions to either side so4 2 minus ions to either side he also they are in the aqueous state so then you can rewrite the full equation so before that if you look at this this is a complete reaction but he also we have charges now you all know a reaction has to be balanced zinc zinc to H H2 that is balance and the charges are also balanced here you can see 2 times h plus so there are two positive charges and on this side we have 2 plus charge so the charges are also balanced you can write the complete reaction where you write seeing solid Plus h2so4 equals giving rise to zinc sulphate equals plus we will have H2 gas so that is the complete reaction now so far we have only been dealing with this type of reaction a metal reacts with acid to give rise to the salt and releasing hydrogen gas you're familiar with that but now you all have understood what really happens when you put a piece of zinc shade into dilute sulfuric acid so I introduce the terms oxidation a species loses electrons reduction a species gains electrons and when there are electrons and charges in a reaction those are half reactions or the equations are known as half ionic equations so one particular reaction can be written as oxidation and reduction that is how we get the electrochemical cell so you need to understand these concepts for students then only you will be able to understand the functioning of a cell properly so we have combine the reaction these are the half reactions zinc becoming zinc two plus losing electrons hydrogen ions taking up electrons and becoming H2 gas those are half reactions and the equations are half ionic equations and when you add them together the electrons get canceled off and you get this equation but since sulfate ions are there in the solution you can write the complete reaction with the all the ions there so a zinc solid reacting with sulfuric acid aqueous giving rise to zinc sulfate aqueous and releasing hydrogen gas so those are the observation zinc dissolves and hydrogen gas bubbles are evolved near the zinc shape is that clear to your student so then I'm going to move on to the next slide again like I said I will be repeating all these reactions so this is what happens they are students first we will look at what happens here here it can be observed that gas bubbles are liberated near the zinc and the zinc strip dissolves gradually SO gas bubbles are liberated near the zinc strip and also zinc strips dissolve gradually let us find the reason for those observations so before we go to that you can remember now we had the beaker in that sulfuric acid and there we had the zinc Strip This is zinc this is h2so4 and you were able to see gas bubbles that is H2 gas and also you were able to see the zinc strip dissolve so zinc becomes zinc 2 plus equals all those were the observations you were able to see the zinc dissolving and going into the solution although you didn't see the zinc going you were able to see the zinc matter dissolving and you were able to see the hydrogen gas bubbles so how did that happen the first reaction zinc atoms that is added in go into the solution as in two plus ions leaving electrons on the metal so that is what we saw here the first reaction that then solid losing electrons forming zinc to plus and going into the solution as into plus aqueous after losing the electron so this is how we write the equation z n solid giving rise to that then 2 plus aqueous losing two electrons so here you can see the electrons get accumulated on the zinc strip that also I showed you now electrons get accumulated on the zinc strip this process can be shown as follows using chemical symbols so this is the process that I have already shown here zinc solid giving rise to zinc 2 plus aqueous losing to electrons then we'll move to the next reaction sulfuric acid dissociates into hydrogen ions and sulfate ions in water this can be Illustrated as follows so sulfuric acid dissociates this is the second reaction sulfuric acid h2so4 aqueous giving rise to h plus aqueous plus so42 minus aqueous I have already written the balanced equation h2so4 equals giving rise to 2 h plus a equals nso42 minus aqueous sulfuric acid dissociates into hydrogen ions h plus ions and sulfate ions in water you have to remember these terms your familiar with them hydrogen ions and sulfate and say so for two minus then what happens there the h plus ions in the solution are attracted towards the zinc strip to capture the electrons on it electrons are negatively charged h plus is positively charged so they get attracted towards the zinc strip that is also something you have to remember h plus ions in the solution are attracted towards the zinc strip to capture the electrons on it hydrogen ions after receiving the electrons become hydrogen gas using chemical symbols this can be written as follows so this is how we can write that reaction 2 h plus ions that is in the equal State take up two electrons giving rise to H2 gas so this is also an important reaction you have to remember this as well so that is another one we will move on to the next one the reactions written as one and two above depicting the conversion of one chemical species into another either by removing or accepting electrons are called half reactions by adding two half reactions appropriately the balanced ionic equation can be obtained so again to recall the half reactions you can remember zinc solid becomes in 2 plus aqueous losing to electrons the first reaction then 2 h plus a equals taking up two electrons to become H2 gas that is the second reaction students I have written this already before also I am rewriting here so that it's easy for us to add them and rewrite without going back to the previous slide that is why I have written it again so if you are asked to explain you don't have to keep on writing it because you will have all your reactions written on one sheet of paper it's easy for you all to look at the reactions half reactions or half equations written above and write it below the full balanced ionic equation but for us since we have it in the previous slides I have written it again otherwise you don't have to write it twice so these are the reactions first and second reactions you can add them together you can add them together so once you add them together you will get zinc solid plus 2 h plus aqueous plus two electrons giving rise to Z2 plus aqueous last two electrons plus H2 gas now always we don't write any state for electrons that I told you all before also and from this you know you can cancel off the electrons you have electrons on the reactant side and the product side so they get canceled out so therefore you can write this equation zinc solid plus 2 h plus aqueous giving rise to Ring 2 plus aqueous and H2 yes this is the balanced ionic equations this is the balanced ionic equations so now all the new terms here you can see the half reactions zinc solid becoming zinc two plus losing electrons and H plus ions taking up electrons becoming H2 gas those are half reactions when you add them together to get one plus two you add them together you will get this equation with electrons but since you have the same number of electrons on either side you can cancel them off and you will get this final equation which is a balanced ionic equation here also they are a ions so it is a balanced ionic equation with that I'll move on to the next slide next let's just consider how this reaction can be represented by a balanced chemical equation now we need to write a balanced chemical equation balanced chemical equation the hydrogen ions h plus were added to the solution by the dissociation of sulfuric acid when sulfuric acid dissociates sulfate ions are also added to the medium in addition to h plus sides but sulfate ions do not undergo any change sulfate ions do not undergo any change during the reaction so we add sulfate to both sides is that clear to your we need that before also so we got zinc solid plus 2 h plus aqueous plus you add sulfate ions so42 minus aqueous giving rise to zinc 2 plus aqueous plus H2 gas and in addition to that you have so42 minus a equals so you add so photo minus a equals to both sides because they are they are in the media from that what do you get you get the next final equation that is the balanced chemical equation where you have zinc solid h2so4 equals how do you get this h2so4 equals these two 2H plus plus so42 minus is H2 so4 plus n minus 2 plus 2 minus that will be canceled off you will get the compa so that then solid plus h2so4 a cross giving rise to minus together 2 plus 2 minus so that becomes at then so4 equals n H2 guess is that clear to you so this is the balanced chemical equation that is the balanced chemical equations balanced chemical equation so we had the half ionic equations then we had the balanced ionic equation and now we have the balanced chemical equation is that clear student so here students we saw all the reaction what happens to zinc when it dissolves then h plus takes up electrons the half ionic equations when you add them together in the previous slide we wrote the balance ionic equation and from there we get the balanced chemical equation so that is what happens when you put a sheet of zinc or a strip of zinc into dilute sulfuric acid the way that I am going to move on to the next slide given above is the complete reaction for which zinc metal reacts with dilute sulfuric acid so here zinc metal reacts with dilute sulfuric acid if the exchange of electrons taking place between the zinc metal and H plus ions during the above process occurs through an external conductor we can produce an electric current so like I told you all what we saw there was exchange of electrons seeing closest electrons h plus takes up electrons so if we can make the electrons to flow through an external conductor then of course we will be able to produce electricity so to do that this is what we need to do now we had sulfuric acidia we only had one metal initially so we had dilute h2so4 that is a plus and here we had zinc solids now if we put another metal into this and if we can connect it by a conductor you can make the electrons to flow through that conduct then of course we can generate electricity that is when we get the electrochemical cell so initially we only looked at this like I told you all there should be two terminals so we only had one terminal up to now if we try to get two terminals two electrodes then you will get one electrochemical set so that is what I am going to discuss after this so with this student I'm going to end this chapter where we discussed what happens when we put a piece of zinc a sheet of zinc into dilute sulfuric acid and you became familiar with half reactions balanced ionic reactions and the balanced chemical reaction so in the next chapter we will see how we can have two electrodes together to produce electric current by making the exchange of electrons to occur through an external conduct external conductor so that is what we will try to do in the next chat to watch these important lessons subscribe to DP education's YouTube channel right now click on the Bell icon to stay updated on the latest lessons Sri Lanka's largest free online school DP education