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Shorthand notation for galvanic/voltaic cells

Video transcript

before we get into shorthand notation let's review the structure of a galvanic or voltaic cell remember a voltaic cell uses a spontaneous redox reaction to create an electric current and so we already know what happens on this electrode on the left the zinc electrode the solid zinc turns into zinc two plus ions so think about an atom of zinc turning into zinc two plus the atom would have to lose two electrons so two electrons are left behind on the zinc electrode let's write out that half reaction so we have solid zinc all right losing two electrons to turn into zinc two plus ions in solution so this would be losing two electrons so we put the electrons on the product side and this is our oxidation half-reaction so this is an oxidation so we lost electrons remember when you lose electrons it's an oxidation reaction or you could also look at the oxidation states those two electrons that we lost these two electrons right here are going to travel along our wire so we have a wire setup and those two electrons are going to move which is our electric current all right so we get an electric current in our wire and those two electrons move over to the electrode on the right which is coppers now we have these two electrons on our copper electrode in solution this is an aqueous solution of copper sulfate so we have copper two plus ions in solution and when those copper two plus ions come in contact with those electrons right we get a reduction half-reaction so let's write it out here so copper two plus ions right are going to gain two electrons gain of electrons is reduction so think about what happens if you add two electrons to a copper two plus ion you get solid copper right so overall overall zero charge so this would be solid copper since we gained electrons this is our reduction half-reaction so this represents a reduction half action so remember loss of electrons is oxidation and gain of electrons is reduction so Leo the Lion goes ger is a good way to remember oxidation and reduction if we add together our two half reactions we get our overall redox reactions so we add these together and we know that the two electrons that were lost by zinc are the same electrons that are gained by copper two-plus so we can cancel those out and so for our reactants we would have solid zinc and we would have copper two plus ions so we write that in here so solid zinc plus copper two plus ions and for the products right over here we would have zinc two plus ions and solid copper so this gives us zinc two plus ions in solution and also solid copper so over time if you think about what happens right we're losing we're losing zinc so let me let me use a different color here so we're going to lose we're going to lose zinc over time and we're going to gain copper all right so we're going to get more copper deposited on our copper electrode so think about more copper or copper or deposited on the surface of our copper electrode so that's our spontaneous redox reaction that's creating an electric current because of the flow of the electrons in the wire here let's go back to our half reactions and think about the electrodes so we know that we know that oxidation occurs at the anode right so this must be our anode and we know that reduction reduction occurs at the cathode so this must be the cathode and a good way to remember this is an ox and red cat right so an ox oxidation occurs at the anode and then red cat let me write that one down over here so edie cat reduction occurs at the cathode all right let's also think about the salt bridge really quickly all right so we have let me go ahead and use red here we have sulfates we have sulfate anions in our salt bridge and anions migrate to the anode so anions migrate to the anode so that's easy to remember that so these these these anions are going to migrate this way and cations migrate to the cathode so we have sodium cations here and cations migrate to the cathode so it's easy to remember what's happening in the salt bridge all right now finally let's think about shorthand notation so it's a little bit annoying to draw out a picture like this every time you want to represent a voltaic cell and so there's a shorthand notation that's used so you don't have to keep drawing things out and so let's go ahead and start writing our shorthand notation first you put your electrode you put your anode so our anode here our anode is zinc so we have solid zinc so let me write that down here so solid zinc next you draw a single vertical line which represents a phase boundary between solid zinc and your aqueous solution of zinc two plus ions so we're going to write our zinc two plus ions in here so we've represented let me use red for this we've represented our zinc electrode and we've represent our zinc two plus ions next we draw a double vertical line and this represents our salt bridge so the double vertical line represents our salt bridge and next we put copper two plus so we have copper two plus let me circle these in green copper two plus ions so we write C u two plus and next we draw a single vertical line again representing a phase boundary because now we put our other electrode our cathode and our other electrode would of course be solid copper so let's go ahead and write that in so we have solid copper right here so the anode the anode is always in the far left and the cathode is always on the far right and so it's easy to remember that because a comes before C in the alphabet so the anode comes on the left side and the cathode comes on the right side and again this is just the shorthand way of representing a cell so instead of drawing out this huge picture if you see this written if you see all of this written let me go and underline it here all of this written in a chemistry textbook it's just telling you it's a telling you the same information that's in this picture