in this video we're going to talk about galvanic cells which are also called voltaic cells so what are they well galvanic or voltaic cells are devices that use a chemical reaction to create electricity specifically the type of chemical reaction that they use is called an oxidation reduction reaction but we'll talk more about that later now galvanic or voltaic cells may be totally new terms for you but I'm willing to bet that you use these devices almost every single day of your life and that's because a battery is an example of a galvanic or voltaic cell there are chemicals inside batteries and those Chemicals React together in an oxidation reduction reaction that makes electricity and this is what powers your cell phone or your flashlight or whatever the batter is hooked up to so let's learn more about these devices and see how a chemical reaction can create electricity okay so I think for the rest of this video I'm just going to call these voltaic cells instead of calling them galvanic or voltaic cells all right so I now want to talk about the parts of a basic voltaic cell one that that you could actually make in the lab so here's what they are first we start with two beakers or containers of water and into one of them we dissolve some zinc sulfate to make a solution and then into the other we dissolve some copper sulfate and make a solution with that so we got these two solutions then we take a piece of zinc metal like this one right here and put that in the zinc sulfate solution and then over here we take a piece of copper metal and we put that in the copper sulfate solution the next thing we do is we take a wire a metal wire and we use that to connect the two pieces of metal together and when we do this something amazing starts happening a electrons start moving through this wire they move from the zinc metal into the copper metal now this is a big deal because moving electrons are what make electricity so when we hook this wire together with the pieces of metal and electrons start moving through it we have electricity we have electricity moving through this wire and what we could actually do is we could take a little light bulb like this and hook it up to this wire and the light bulb would turn on because there's electricity moving through this wire now to be really specific there's one more part of the voltaic cell and that's a little tube called a salt bridge that connects these two solutions we'll talk more about the salt bridge at the very end of this video but right now I'm going to leave it out because I want to make sure that we keep things simple so this is the basic setup of a voltaic cell now I want to zoom in so that we can see the atoms and electrons in the metal and in the solution and understand what's causing electrons to move along this wire and create electricity here's our magnification of the different parts of the voltaic cell we can see some of the atoms in the metals and in the solutions so let me show you what's what this is a magnification of the area here these zinc atoms are on the edge of the piece of the zinc metal and then these zn2+ ions are in the solution they're part of this ZN so4 solution I'm not showing the S so4 here I just want to focus in on the zinc so zinc ions in the solution and these zinc atoms in the piece of zinc then over here we have these cu2+ ions that are in the CU so4 solution they're dissolved here and then these copper atoms are on the edge of this piece of copper here okay so we've got a wire that connects the zinc and the copper and we've said that when we hook everything together a electrons start flowing through this wire well why is that well when we connect these two pieces of metal with a wire it kind of starts a tug of war between the zinc and the copper they're having a tug of war for the electrons one of them wins and one of them loses it turns out that cu2+ these atoms here cu2+ has a really strong pull for the electrons but then on the other hand zinc these zinc atoms zinc has a weaker pole for electrons so in this tug of war cu2+ ends up winning let me show you how this happens so cu2+ really wants electrons so it's kind of like it calls over here to zinc which has a weaker pull on the electrons and says hey zinc give me some of your electrons and zinc's kind of weak so it's like oh okay and what happens is let's say this zinc atom here gives away two of its electrons and these electrons enter the wire and move towards the copper now when zinc gives away those two electrons it causes its charge to change it's lost two electrons so it gets a positive charge and it becomes zn2+ now changing from neutral zinc to zinc 2+ has a big effect on this atom and that's because neutral atoms make up solid metal But Metal ions usually dissolve in water so after this zinc atom turns into zn2+ because it lost these electrons it's no longer part of this solid metal anymore and it floats off it dissolves into the solution okay so that's what happens to the zinc then over here these electrons make their way down the wire to the copper and one of these cu2+ ions which really wants electrons is going to come over here and these two electrons are going to be added to the cu2+ ion gaining these two electrons is going to get rid of that 2+ charge that was on the copper and that is going to turn it into a neutral atom which means that it is no longer going to be able to dissolve in solution and it's going to become part of the solid copper metal here okay so that's what happens to the Copper now notice that for this whole process to happen electrons have to move through this wire and that's where the electricity the electron movement comes from let's see that one more time so zinc loses two of its electrons here those move Through the Wire loss of those two electrons causes zinc to take on a 2+ charge it is then going to dissolve in the solution these two electrons are going to move over here to copper and one of these cu2+ ions that really wants electrons is going to come it's going to take them in and that is going to get rid of the cu2+ it's going to get rid of the 2+ charge and this neutral copper atom is now going to become part of this solid piece of copper metal so that is where this electron movement Through the Wire is coming from zinc loses these two electrons they move through the wire creating electricity they come over here and they join up with a cu2+ turning it into neutral copper we have these electrons move moving Through the Wire here creating electricity so that is how we get electricity from these electrons moving from the zinc over here into the copper and if this happens long enough we actually see these two pieces of metal change right like these zinc atoms keep coming off of this piece of zinc so it's essentially dissolving and over time what we'll see is that this piece of zinc actually starts to dissolve it gets smaller and smaller but then on the other hand those cu2+ ions are coming out of solution and are attaching to the solid copper and so they're going to make this piece of solid copper bigger and bigger and so if we let this voltaic cell run for long enough we'll eventually see that these two pieces of metal actually change size and shape here are some diagrams for the process that's happening in the voltaic cell I wanted to describe what's going on in terms of oxidation and reduction so over here one of these neutral zinc atoms is losing electrons so that means that oxidation is happening on this side of the voltaic cell and over here this cu2+ ion is gaining two electrons to turn into into a neutral copper atom so reduction or gain of electrons is happening over here now we can give names to these two parts of the voltaic cell based on whether oxidation or reduction takes place so the cathode is the name that we give for the site of reduction where reduction happens so reduction is happening here which means that the piece of copper is the cathode the site of reduction and the piece of zinc over here is where oxidation is happening so the piece of zinc is going to be the anode so reduction at the cathode on copper oxidation at the anode on zinc now let's write reactions for the two processes that are happening here okay first let's write the reaction for reduction we're starting with CU 2+ and this cu2+ is dissolved in solution so I'm going to write that with an AQ for aquous after it to show that it's dissolved in solution now this cu2+ gains two electrons so I'll write plus 2 e minus and that gives us a neutral copper atom so I just write CU with no charge after it that shows that it's neutral and then it's part of the solid metal so I write an S after it so this is the reaction for the reduction process over here the reaction for the oxidation process we start out with a neutral zinc atom and this neutral zinc atom is part of the solid piece of zinc so I'm going to put this s here for solid now it loses two electrons to show that we lose something in a chemical reaction we put it on the other side of the arrow okay so I'm not going to write anything right here I'm going to put this Arrow I'll leave the electrons for last losing the electrons turns the neutral zinc atom into a zn2+ ion zn2+ that is now dissolved in solution so I'll write AQ here and then finally to show that I lost those two electrons here I'll put Plus 2 e minus on this side so this is the reaction for the oxidation now these two reactions that I wrote we call them half reactions because each one of them tells half the story of the oxidation reduction process and we can actually give names to these two parts of the voltaic cell as if each one of them is half of the big picture we call this the oxidation half cell it's half of the voltaic cell where the oxidation is taking place and we call this the reduction half cell it's half of the voltaic cell where reduction is taking place and it is these half reactions that show what's going on in each one of the half shell in each in each one of the half cells I said half shells was like Teenage Mutant Ninja Turtles coming back to H me from the 80s anyway we have these two half reactions and we can put them together to get a net ionic equation which shows the overall oxidation and reduction process we start with solid neutral zinc and cu2+ ion and then at the end of the process we're left with zinc 2+ ion and then we have solid copper this is the ionic equation that we get from adding together these two half reactions now when we're talking about voltaic cells we're often asked to represent them in cell notation which is a shorthand abbreviation of the chemical reactions in the voltaic Cell It's a way that we can show what's going on without drawing a picture of the whole thing okay cell notation is sometimes referred to as a cell diagram just so you know so here's how we would write what's going on in this voltaic cell using cell notation we start on the left with the oxidation process okay how does the oxidation process start well I have the half reaction up here it starts with solid zinc okay so I will write ZN solid right here that's how the oxidation begins then I put this line here and I show what we end up with in the oxidation process which is zn2+ okay so zn2+ and that is dissolved in water it's part of the solution it's aquous so this shows the oxidation process that happens in the half cell over here okay then I put two lines like this and these two lines represent the physical boundary between these two half cells or you can think of them representing the salt bridge okay now on the right I put information about the reduction process so the reduction process begins with cu2+ aquous cu2 plus aquous and then I will put another one of these lines and the reduction process ends with CU solid so there CU solid so this is how we can sum up what's going on in this voltaic cell using cell notation we have the oxidation process and then two lines showing the boundary and then we have the reduction process so finally we've talked a little bit about the salt bridge I said we discuss it at the very end so let me take a minute or two and explain what the salt bridge is what it does and why it's important in a voltaic Cell the salt bridge helps to balance out charge in the voltaic cell here's what I mean the two solutions are made up of both positive ions and negative ions I didn't show the negative ions before those are these yellow things I just showed the zinc and the copper but along with these metal ions are these polyatomic ions sulfate s so42 minus it's a sulf with four oxygens and the whole thing has a 2 minus charge I didn't want to have to keep using this thing so I've just abbreviated these as s so42 minus but the point is the negative charge from the sulfate balances out the positive charge from the zinc or from the copper so right here in my two half cells the charges are balanced out but let's look at what happens as the voltaic cell begins to run for a while okay over here these zinc atoms are going to give electrons to Copper so they are going to end up with a charge I'm not showing the electrons here but electrons are getting sent up here as these turn into zn2+ ions and as they enter the solution now over here as electrons come over these cu2+ ions will turn into neutrally charged copper atoms and attach to the metal now look at what's happened to the charge here okay now we have all of these zn2 pluses but we have only a few of the S so42 minuses so after just a little while positive charge really begins to build up in this half cell and then over here as the positively charged ions like this lose their charge by gaining electrons and turn into neutrally charged copper now there are a whole lot more s so s so42 minus than there are CO2 plus so a negative charge begins to build up on this side and if this positive and negative charge build up too much the cell can't run anymore it can't continue to make electricity so that is where the salt bre Bridge comes in let me get rid of this wire and show you what the salt bridge looks like here is the salt bridge it is a tube shaped like an upside down U that in our case is filled with sodium chloride and you can see that na+ and the CL minus ions now at the ends of the salt bridge there are cotton plugs a little bit of cotton there and the cotton prevents the solution from just pouring out into the half cells but these ions are able to slowly pass through the cotton plugs and here's what happens we said that negative charge is going to start building up in the half cell over here and so the positively charged na na+ is going to begin moving over into this half cell to help balance out the charge so the na+ ions are going to begin moving in this direction to balance out the negative charge and over here we said that positive charge begins to build up the CL minus ions are going to begin moving through the salt bridge to come out through the cotton and help to balance out the positive charge that builds up on this side of the voltaic cell so over time what we're going to see is we're going to see that the cl minuses move in this direction to balance out the positive charge that builds up here and then we'll see that the na pluses begin to move to this side to balance out the negative charge that builds up here a salt bridge helps to balance these charges to make sure that they don't build up too much and that would prevent the voltaic cell from being able to work wow so we just learned so much about galvanic or voltaic cells okay so here's the basic structure of a voltaic cell we have the zinc sulfate solution here copper sulfate solution here we have zinc metal and copper metal now when we hook this all together electrons start flowing from the zinc to the copper and that's because copper that's in the solution has a strong pull for electrons whereas the zinc has a weaker pull so the copper wins as electrons move from the zinc to The Copper they are lost in the zinc so oxidation takes place and they're gained here in the copper so reduction takes place over here we call this the oxidation half cell and we call this the reduction half cell because oxidation is happening over here the piece of zinc is the anode because reduction is happening over here the piece of copper is the cathode then finally we can write half reactions for the two processes that are happen happening in the different half cells here is solid zinc losing two electrons because they're moving out to turn into a zinc 2+ ion which is going to enter the solution and then over here cu2+ ion that's in the solution gains two electrons and turns into solid copper it's going to attach to this metal right here and then finally we can sum all of this up by writing this uh this cell diagram or cell notation which shows everything that's happening in a shorthand abbreviated form ZN solid then a line zn2 plus aquous this shows the oxidation part then we have these two lines representing the salt bridge or the boundary between these two cells and then we have the reduction part cu2+ line giving us CU solid so that is how a device like galvanic or voltaic cell uses a chemical reaction to create electricity