Lecture 21. Electrochemistry Pt. 6.
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Lecture 21. Electrochemistry Pt. 6.

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Part Number 
21

Number of Parts 
26

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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. 
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University of California Irvine (UCI)

Release Date 
2013

Language 
English

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Abstract 
Ramesh D. Arasasingham, Ph.D.UCI Chem 1C General Chemistry (Spring 2013) Lec 21. General Chemistry  Electrochemistry  Part 6 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 acidbase equilibria, solubility equilibria, oxidation reduction reactions, electrochemistry; kinetics; special topics. Index of Topics: 0:00:50 Ecell and K 0:04:25 Calculate K for the Equilibrium... 0:12:40 Nerst Equation 0:17:47 Calculate Potential of Daniell Cell 0:23:01 Galvanic Cell Review 0:29:52 Electrolysis (Electrolytic Cell) 0:42:52 Amounts of Products of Electrolysis

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it but OK ,comma can I have a room detention please and so on was going and before I begin I wanted to know of any questions all right so you guys remember on we talked about the relationship which we in the cell potential and equilibrium constant last time and we in expression and this
00:43
comes from we know that the relationship between free energy and equilibrium constant is Delta Jeannot reaction equals minus R T L and case we let this last quarter we looked at the and we look at the relationship between free energy in the equilibrium constant now we also know that Delta Jeannot reaction equals minus and have even on south that's the relationship between the cell potential in the free energy and therefore we can say and have you not sell equals negative RT Alan Keyes and so now we can rearrange the get rid of the Commission signs we can even get rid of the person a L the walls and have work t he nods for me he said he sell equals party over and Alan Keyes said depending on what we want calculated he can rear this equation to get rid of this or that and then we said that the view are hours a constant it's 8 . 3 1 4 5 jewels press Calvin from all we said that temperature is absolute temperature and room temperature of history I'm sorry I can't temperature is Kelvin temperature in Everett 25 degrees Celsius then this would come out to be 298 . 1 5 Calvin and lastly we that's it is fairly constant which is 9 . 6 arms 4 8 5 cool alarms from all and so we put this in and we end up with our priority over an equals 0 . 1 0 2 5 6 9 3 2 0 . 0 2 5 6 9 3 balls and put that value in there and so it should end up with is Alan Keyes equals and was 0 . 0 2 5 6 9 3 balls before we can say we can write that like that or we can say not sell equals 0 . 0 2 5 6 9 3 balls divided by 10 times Alan Keyes or so now we have a relationship between the equilibrium constant in the sell potential so let's take an example where we apply this case determined that problem on the on the worksheet and and surviving change this to the problem you can see that you're asked to calculate case which is equilibrium constant for the reaction that we've been looking at all along which is the reaction in the Daniel cells and we know that the seller potential for the Daniels cell is 1 . 1 0 volts and survival account equilibrium constant canaries see that this would be making use of this equation over here organs that Alan K. equals and not sell over 0 . 0 2 5 6 9 3 cell look said Alan Keyes equals 1 In which is the
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number of electrons being transferred the not cell divided by 0 . 0 2 5 6 9 3 walls now we know we've seen previously that the downhill so we know to electrons having transferred in and gives you the number of moles of electrons being transferred so that would be too the cell
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potential we know for that is 1 . 1 0 volts now if they don't give you potential you look at the balanced equation you figure out what is the reaction of Indiana what is the reaction of the capital would you go electrochemical series of the table of reduction potentials and you add them together you take the reaction for the capital would you take the reactivity and notice which the sign add them together and that will give you the cell potentially going to get the cell potential from the tables you figure how many electrons are being transferred
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and then you put this in here and the survey's 0 . 0 2 5 6 9 3 volts holes in
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walls would cancel out which gives you 85 . 7 right and then by taping the side of that today comes out to be 1 . 5 times 10 to the 37 so you can see but these reactions the equilibrium lies entirely on the product side so includes establishing get lots of lots of products being formed all right now you look at this reaction can receive that we're looking at case OK it represents the concentration the products divided by the concentration of the reactants are right now they're solid C and we know that the of solids the not include them in the aquarium expression so K is really the concentration of zinc to plus signs which the products divided by the concentration of copper to all right and so
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this is 1 way in which you can determine that equilibrium constant for a reaction because the center which you do is you can look up the appropriate oxidation reduction reactions and from that you can get elected you know from the standard reduction potentials you can figure out which is oxidation half of the reaction we can figure out what is a reduction half of the reaction to figure out the the potentials that correspond to the oxidation half the reduction have added together .period the cell potential plenty cell potential if you put in this equation and you can figure out the value of equilibrium constant alright right yes why king and his wife is it wiser to significant figures because of accident but we are going to 3 significant figures here are right hand and so if you work strictly keeping track of 6 figs and you just take the decimal because you're taking the inverse farther back OK so strictly speaking you would end up with a number that is once and for all right but I'm just hanging over so here are not keeping track of 6 things aren't so you just doesn't make sense everybody this is we're taking the inverse log of this number and we go from the logs scaled to the regular scale you will look at the decimals all right and so they would turn out that this number should be here to be practicing things shouldn't happen 1 significant figure guidance OK so we talk about the fact that for any reaction you can figure out what the equilibrium constant is as long as you can identify the opposition have the reduction half of their reactions occur no I wanted him summarize so the relationships that we looked at an adult when you are looking at the wooden it's alright any water relate delta G which tells the utility of spontaneous reactions you know delta genes should be negative is on spontaneous reaction you would be positive and the relationship between Delta genes and equilibrium constant was given by this equation where we adopted G equals minus RTL and caring and if you want to look at the relationship between delta G and sell potential we know that reaction that relationship is given by Delta G equals minus and not sell and then you will look at the relationship between the cell potential anchored that's the equation that we derived all right today and so whatever you have to convert from 1 to the other this kind of trial shows you the relationship between the quantities the relationship between Delta gene on the cell potential an equilibrium constants in resolving problems depending on what you need to calculate you can use that to figure out the relationships Zakaria when Soderling said that we're going to look at that sort of worried about the last topic that we look at it from the galvanic cells and that is the nearest equation they sell you're copying this I give you a moment to copy down all right so yes yesterday that comes from the limits RTL always at Soros the gas constant which is in SI units residuals for Calvin from all at times team which is the temperature which 298 . 1 5 in an effort is very constant OK so put those numbers then you should end up with that OK so if we now move on to looking at the last topic that we want look at what we do a galvanic cells and that is what we call the nearest equation know what we started looking at galvanic cells were the things that we talked about was that for any bad really or any galvanic cell we know that as the batteries being used up at some point the battery gets spent all right and so usually what happens is when we deal with galvanic cells we start under standard conditions severely with the Daniels cell wouldn't have 1 will accompany ,comma concentration of zinc ions 1 molar concentration of copper ions in and we have zinc metal and copper metal and at that point we connect the CA because the concentrations are all under standard conditions the voltage that measure and that will be there would be 1 . 1 0 waltz OK now once the battery starts working what's gonna happen is the concentrations of the change the concentrations in Donald where we have the zinc their concentrations I wouldn't change and on the other side of the copper iron concentrations were changed and so as the concentration changes the cell potential starts changing as well all right and as the reaction proceeds of the sale potential changes as well until Indiana the batteries spent in when the battery spent we said that in equilibrium has been at established established with delta G 0 are right and solar the cell potential 0 as well so what happens is when the battery is spent the center what happens there's that inequality has been established and the reason is that as the reaction progresses the concentrations in both those chambers Indiana the capital will be changed OK so you want to look at the dependence of the cell potential on concentrations then we look at the nearest equation are itself where the nearest equation gives you it is the formula for predicting for predicting that variation but this cell potential when the concentration of of concentrations and pressures is expressed by the nearest equation all right and once again it will be start with the equation that we learned implement amendments now everyone to look at the change in free images as the concentrations of reactants and products change we said that is given by the equation delta G Reaction equals Delta G reaction plus Archie Bell and In remember we said as the reaction approaches equilibrium if 1 look at how free energy changes as the concentrations of your reactions in part partexchange were using Q because we have an established equilibrium yet the reaction is proceeding
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and if you want look at the dependence of the free energy changing concentrations of reactants this is the equation that we use our right now would apply this to electric chemistry and electric chemistry we know that Delta GE reaction will give you minus a and Delpha Jeannot reaction so this there's free energy under conditions were you not under standard conditions this is free energy under standard conditions which gives you the difference of free energy between pure reactants until products are right and this case this'll be understand it states the cell where everything is 1 molar concentration so this will be and have you not sell another take these 2 values included in that equation sort out however is have sell Yukos minus and have you not sell plus parity Alan Q and if I rearranges equation you can see the Sal calls not sell 900 take the science and flipped the signs around so the miners are she or where N F L N Q and we call this the nearest equation in essentially what this equation tells us is that as the concentrations of yourself and your reactions and products In cell changes if you want to look at the dependence of the self tend to have his itself to change as you concentrations of the react and products very that's given by this equation many guys remember Archie over at half is 0 . 0 2 5 6 9 3 bowls by place that in this equation and I can say these cell equals the nonselfie minus 0 . 0 2 5 6 9 3 balls for over 10 times Ellen if you replace all the constant and put the values that correspond those Constance Baker Motley that number and I can replace those numbers that his party over half with that so now let's apply this in a problem OK and so let's take this example for were asked to calculate so calculated the potential at 25 degrees Celsius of Adandia in which the concentration of zinc alliances . 1 0 multiple leaders and added the Cup Orion's is . 0 1 0 0 1 0 moles per liter so we were calculating the standard cell potential we know that's the 1 . 1 0 waltz right and that we can get from the tables of standard reduction potential of we can calculated by the standards cell potential would be the reduction potential at the Catalan plus the reduction you know foot that around and the potential at the end of any sum them up if it's going to be under other conditions there will use the nearest equation so we know that if you have a let's look at what's given to us we know that the concentration of zinc iron is 0 . 1 0 Muller the concentration of copper mines is . 0 0 0 1 0 more and we now but the standards of potential for the Daniel cell is 1 . 1 0 World now what we need to calculate years the cell potential when it's not under standard conditions right and so we know that yeast cell equals the not minus 0 . 0 2 5 6 9 3 Vols divided by an times Ellen I write with which it is not so minus 0 . 0 2 5 6 9 3 holes divided by end and we know Ellen Is the concentrations of the reactants and products and we offer the Daniel sell the reaction that we're looking at is ink solid plus copper to plus requests giving me zinc to plus the quest plus copper solid so the equilibrium expression for the expression of a Q would be the concentration of zinc iron so divided by the concentration of copper ions are that's what he would be and therefore I can say said equals 1 . 1 0 volts which is not sell minus 0 . 0 2 5 6 9 3 walls divided by an and remember any gives you the number of holes electrons are being transferred so how many moles of electrons are transferred and that balanced equation 2 right Olympic 2 there and then there's the the Allen times the concentration of zinc is . 1 0 Moeller divided by . 0 0 1 0 Moeller a right and so on but I'll end up with ECL equals 1 . 1 0 walls minus and if you put all these numbers into the equation and software if it comes out to be 0 . 0 0 5 9 balls and you subtract that it comes out to be plus 1 . 0 4 walls right so you can see the cell when you have 1 molar concentration of zinc and 1 molar concentrations of copper and that's the cell potential staff under standard conditions will be 1 . 1 0 walls but as the reaction proceeds now you can see the cell potential decreases as the concentrations change in both chambers are right and this will be the cell potential when the concentrations are the ones provided there OK so they get a problem where you're asked to calculate the change in cell potential as the reaction proceeds and you know the concentrations in the 2 chambers in the air in the chamber where you have the attitude in the chamber where you have the cathode would now you can affect calculates the selfprotection but so that kind of completion looking at galvanic cells and remember galvanic cells to take advantage of a spontaneous reaction OK now we have a look at cells that make use of a non spontaneous reaction and we call this electrolysis or we call them electrolytic cells are right so would you look at electrolytic cells or electrolysis the hit of the and let's just talk about this a little bit so in
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the past we looked at the galvanic cell and we looked at the Daniel self in detail are right and we see this picture Of the Daniel cell now Daniel cells take advantage of a spontaneous reaction is natural tendency for the reaction take place and because is a natural tendency for these reacted to take place we said we construct this device so that instead of bought the reactants and productivity in contact with each other within a set it up so that wouldn't take advantage of the spontaneous reaction but now we're gonna have forced electrons to the wider and as a result will be the end up with a with the current being passed to the why not look or electrolytic cells will we look at is the worst process and now all we do is we not interested in a spontaneous reaction what we do it as we take this set but now what connected to apostles so rather than take advantage of a spontaneous reaction now you this going to connected to a battery or plugging into a source of electricity and all they do is with reaction to go in the opposite States of electron flow member before a spontaneous reaction electrons flow this way now we're going to forced electrons to go in the opposite direction and because we're forcing the electrons to go in the opposite direction now what was the Arnold becomes the capital to see that now what's happening is over here at this electoral lecture getting pulled in all right and so electrons get pulled and so now what happens there is this there is no longer an oxidation now where the oxidation to used to take place have a reductions are right now what's going to happen because of a force of electrons in the opposite direction and of forcing it by using an external power source that external source of current and will be forced to go in the opposite direction so now what's been happening because we're forcing electrons go this way now the reaction that would take place here would be a reduction so instead I producing electrons now the zinc twoplus irons will pick up 2 electrons to give you zinc solid and this becomes the cathode and over here now electrons of flowing out of here as a complete the circuit electrons of flowing out of here so now what happens is copper solid will pick up 2 electrons to give you 2 plus and this becomes the to see that and so we do it is by using an external source were no reversing the whole process now this is the underlying principle which it in rechargeable batteries all right so when you purchase a battery now it's an unused battery and will say they were starting with everything under standard conditions if you start with a galvanic cell and you start with 1 molar concentrations of on both sides during a standard conditions now this cell will produce a voltage of 1 . 1 0 volts all right now as the batteries keeps functioning of the concentrations of change so the cell potential From the standard conditions will start getting lower and lower and lower and at some point the battle get spent in the batteries spent it means that it's established equilibrium and that's why there's no self potential 0 OK I know what you do is you rechargeable battery you take it and you put it in the charges you plug it in In a sense what to do in the universe in the process so now the concentrations it's going to go on the reverse direction and members initially as the battery gets spent what's going to happen is there you have think I use the concentration of zinc go I'll go up as more and more zinc oxide and didn't have a zinc deposit will be here in a week here you don't start Delaware copper deposit on this side so because copper is depositing you can see the concentration of this goes down over here you have the zinc metal increasing so the concentration goes up so a galvanic cell the zinc concentration goes up the couple concentration goes down to see that and so your concentrations change until the battery spent and now you have different concentrations of both our right when you reversed the process now what happens is they often go back to 1 more concentration again because you're reversing the reaction now and so remember the zinc ions that will form the concentration when I now will go back to the solid and over here the cover that was deposited 1 now from copper iron and so now you're you're just running it in the worst process until you reach standard conditions and now your batteries read once again you guys get that yes you will see it's it's being reversed right so what's happening here is that what used to be the Arnold is the cap on May electrons being picked up yes I'm sorry yes you're right I still here embrace so fast enough paying attention a son beside it becomes the analysts what was captured becomes the analyst and vise versa that said no it would ideally with electrolytic cells now so this is the idea behind rechargeable batteries they were dealing with electrolytic cells we no longer have to keep these 2 chambers separated because remember the principle behind galvanic cells was to keep them separate so they don't react with each other directly and chided channeled electrons to the wire In the electrolytic cells in devising electoral accelerated rather energy rechargeable battery you just look at electrolytic cells alone because we are controlling the direction of the electron flow we do not have to keep the 2 chambers separate yourself because now when acting invented it was spontaneous reaction we're taking an external power source to the reaction in a certain direction so we have full control of the direction of the reaction so if you take electrolytic cell then you want design electoral itself not a rechargeable gallon itself for example then what you would do is this is what electrolytic cell looks all right there both in 1 chamber now by convention where diners try to keep that handled on the lefthand side so this would be the an odor and over here we'll have the capital all right and wouldn't connected to a power source are right where this would be the positive and that would be the negative all right and will enforced electrons to flow in this direction all right and so what will end up with is this is where the oxidation will take place and this is where the reduction will take place so this is the an old alright
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so can oversee that I do not know how long I have to keep them into separate chambers I can keep electrodes in the same Chamber because now I have full control of the direction of the reactions are right and the external current is going to force the reaction to go in the direction you wanted to all right and there is no concern about them reacting directly with each other yes yes so you don't find is a little confusing because what I did was I'm taking all right and that and taking the set up and had undoing this year and because we always draw everything with the added on the left side of the the Capitol the rights I do understand that so I took this sound this is where some people get a little confused because reversing the reaction but actually doing as flipping it over because we always keep the animal on the lefthand side in the capital the hand side to see that and so this is what I'm doing all right and I flipped it over so that I could them on the same side because you know that's where the oxidation always takes place but in reality we've actually reversed it all right and we no longer have to keep the 2 chambers separated from each other because we're not taking advantage of spontaneous reactions were actually controlling the direction of electrons flowing were controlling the direction of the electron flow we don't have to keep the 2 twochannel timber separate we do not need a stoppage anymore all right and therefore would you end up with is this drawn here came so you can see that this site will be the copper so the will now be the copper electrodes and the catalog will be the zinc electrode all right and the annual enhanced the oxidation so copper solitude will go to copper to plus plus 2 electrons here where the
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oxidation takes place on the reduction side wouldn't have now that the 2 electrons being picked up because that's where the reduction takes place so you have to to zinc to players picking up 2 electrons to give you a zinc solid to see that sells essentially what we've done is we've just drawn but we reverse the 2 electrodes what was and what used to be the zinc now the enters the copper and a cap that used to be copper but now the capital is is zinc that so now if I wanted to calculate the potential for this reaction can only the sign is when we fled all right so what we have is that the all have copper solid going to cover 2 plus 2 plus 2 electrons remember this is the oxidation and therefore if I want write the potential that corresponds to the best I would turn the tables picked the value that corresponds to that because it's an oxidation and underfoot the sign and sign would be a negative 0 . 3 4 vaults right in and galvanic cell this would be the reduction in therefore for the sign would be positive I write the value that you get from the tables of a plus point 3 4 walls but now because this is the oxidation effort sign around now on the side of it by Take the Capital you can see that this is Inc to plus picking up 2 electrons to give using solid the reduction and this is the value that I would take from the tables and in the tables you look at this value this is negative . 7 6 walls all right so far this reaction you can see that copper solid closing 2 plus gives me copper to plus plus zinc solid and you not sell for this would be negative which is negative 1 . 1 0 waltz to see that electrolytic cell your cell potential comes out to be a negative because this is a non spontaneous process which driving using an external voltage that can oversee that have I want this reverse reactions take place I have to supply a minimum of 1 the 1 . 1 0 volts in that direction you see that to be made in minimal amount of external voltage that needs to be supplied to drive reaction in this direction will be 1 . 1 0 walls and everything that but it turned out in practice you have to actually supplied more right so it's not like you have to supply exactly the amount that's required you actually have to supply an extra amount to get the reaction to go and the difference between the US and the actual value that we supply is :colon although potential so it's like you have to apply depending on the substance that makes up that lecturer so it using copper and zinc now each electrode has a value that's available in tables and Minnesota the lights in the nite .period 6 balls all right said you want to get this to go in this direction not only do you need to supply an external source of 1 . 1 0 balls but you may have to supply a little bit extra which is approximate like . 0 6 walls which is called the old potential so you would have supplied this plus the legal potential and so you have to supply something like 1 . 1 6 balls to get the reaction to go in in that direction as an accessory and you can read a textbook and give you like these are standard values over potential standard values that are listed in Tables a textbook has like for platinum if your of the electorate is a platinum they give you what the value is and you can look at different materials and model potential is very different materials in the center where it is is that you have to supply more than what is required is the minimum amount that's required to get it to go in the reverse direction did you guys get it all right so as did another example let's say that we have electrolytic cell and in this electrolytic cell let's say the NO is where now they opted not to issue takes place and you can have too minors give new C O 2 gas plus 2 electrons and if you look at the values for this in the table it's about negative 136 if you have at the cathode you have magnesium you have energy to class 8 quest picking up the 2 electrons to give you magnesium metal and if you look at the tables for this value it set a cap it's where the reduction takes place and its value comes directly from the tables and therefore if you want the whole cell potential for this you added 2 reactions out so you have to see a minus plus energy 2 plus giving used to see and unsealed to gas plus magnesium solid and this will come out to be negative 3 . 7 2 OK so the same underlying principles that we will the galvanic cells applies here but you can see that in each instance here now yourself potentially overall sales potential will have a negative value because it is not spontaneous and so you can now no the minimum amount of voltage that needs to be supplied to drive the reaction in the opposite direction OK now the electrolysis the underlying principle electrolysis or in an electrolytic cells is what is used in the industry call electroplating all of you heard about you know you can buy jewelry that's left to plated so electroplating means that no 1 can make a necklace out of something like mine which is relatively inexpensive and then you take 18 carat gold for for example and you like to play the surface with our right and this is the end like this is how electroplating is done because what you do it this can you see that in this process let's take this 1 what happens is magnesium is being deposited at the Capitol so center where it is if you want electroplating won a magnesium schooling for example you take them as steel or an Iron Spoon and that would be a capital cell that the shape of the spoon is the Catherine that's dipped in the solution and now you supply the appropriate Khan the voltage all right with real potential and you drive the reaction center what happens at 1 and you can see that chlorine gas is being produced supplying us with this command will bubble out at the other end your school given deposit magnesium on and center where he will form it is a thin layer
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of magnesium on this phone and it's stopping you take this point out if you want a goldplated school center when it is against Poland is your capital but now solution you would set it up so that you have gold dissolve gold irons in solution and goal lines were deposited on the school so that now you have an electric traded small you seem silverplated platters that's exactly what it is you can build is the platter you make that the plan out of the inexpensive material like iron ore aluminum or whatever and on top of that given an outlet to plated with silver or gold the whatever material is and that's what electroplating as is really taking advantage of electrolytic cells recall that let trousers OK nonetheless that that wouldn't look at it is that you should be able to go calculated so I show you how to calculate the minimum voltage that you need to drive the reaction in the opposite direction so if you want this process to take place you know that you have to supply the minimum amount of the voltage and on top of that you have to have you will potential and we looked at the fact that electrolytic cells on that list if you don't need to use your view that the of salt bridge alright everything can be 1 set up because we have full control of the direction of the floor the like of electrons are right and the circuit is completed by you know you can have Catalans moving in this direction you have and nines moving in this direction and so because you have cannons in and I that solution as they moved toward the beach electrode and as they Art reacted those electors now you have occurred since completed within that set up a case that the last thing they were going to do is actually a type of calculation that we carry out and this is given by this handout that I placed on the class websites so now if you want to calculate the amount of substances that are deposited during electron itself so we will look at calculating the amount of products of electrolysis cell remember said at the Capitol is where we use deposit solid materials so you can you know you can lecturer played using any like to win any medal right at any metal that you desire could be gold silver could be aluminum right whatever material you want and so a convenient calculated action that would carry out its we wonder how much of the material actually deposited on the surface right and when you do that as the calculations are in this way so the calculations are based on is a lot of trawler says and what it's saying corridors that law is that the number of moles of product formed by an electric current is state geometry equal and the number of moles electron supply so you know the current that you're supplying then from the current 10 supplying can figure out the number of moles of electrons that he supplied you know the number of mold electrons have supplied remember the half reaction tells us from the half reaction we know that every mall electron that sticking out we know how many more walls of solid would be deposited to see that so that's kind of but that's what we're doing so that start with the current that we supplied and from the current we're going to try to figure out how many malls of electrons have supplied to that and so you start with the amount of electricity and electricity is always given in units of MPs are to the current is given in terms of Ampere and how long the time all right into that gives you and the time they were using as per 2nd alright so if you want to know what amount charged that supplies the charge always the continent years times the time in seconds so if you take the current that you supply and multiply that by the time in seconds which you end up with is the charge supplied and that is new to cool warms up and hear tied 2nd 2nd is actually called that is so now you've taken and here multiplied by the time now you know what the charges supplied is which is Colom's the factories ,comma constant gives us the the charge per 1 mol all right so can they can erase that final the toll charge and I know charge from if I divide the total charge charge removal I am not aware the number of malls it's like dividing mass Bible amassed more masses grants from all here instead of mass animal amassed we have charged and charge from all to do take the charge and abide by charge from which is is constant which you end up with this number of walls of electrons that have been supplied so that we can do is so you can see the malls of electrons is always the charge supplied which isn't qualms divided by the fairly constant which is that right and that would give you the malls of electrons systems would you do is you start with the amount of electricity and the time you can read that too the charges in qualms you divide by Friday's constant you end up in the malls of electrons went you know the mold of electrons look at the balanced equation stake image of the balanced equation and from that you can cap of electrons to molds of products all right once you know the malls of products have you can wear molds of products to Gramercy multiplied by the Moeller amassed so now I wanted to take 1 example of a problem where you apply this so this is like story magic problems and so if you turn to the West once again when I want you to be careful and don't get distracted by sort a distracted us OK show this problem and you read it looks much harder than it really is right and that's because there's some distracted as their 2nd distracted from the real goal where you have to tell yourself it I need to go back to fundamental principles into solve it from what I know apec Celestica look at this can aluminum is produced by electron wasn't so we producing aluminum by the electrolysis aluminum oxide dissolved in molten Korea like sold Cray light is the solvent so you had a lot of dissolving aluminum oxide and that substance cap with the massive aluminum that can be produced in 1 day in electrolytic cell operating continuously at 1 times 10 to the 5 amperes OK so essentially what you're looking at is don't get distracted which looking at it as you looking at aluminum starting off as theirs right is
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depositing as aluminum solid city of aluminum oxide dissolved in there and is aluminum oxide is is being deposited as aluminum so I need to know and I need to know it How many electrons are being supplied all right and so can only see that if you look at the if I assigned oxidation numbers can ever say that this is 3 times negative too therefore in each of these aluminum's will be plus
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3 you said 6 on the site 6 miners on the side you look at it as what is the oxidation number of aluminum so
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can oversee that when aluminum goes 2 aluminum solid How many electrons involved each aluminum Adam Beach aluminum iron goes from plus 3 2 0 all right is that a reduction or oxidation reduction and you know that 3 electrons are being pissed that for each were looking at 1 aluminum iron each aluminum iron will pick up 3 electrons so that means for every mall of aluminum that's deposited it needs 3 malls electrons can the center what's happening is that aluminum 3 threeplus is picking up 3 electrons to give me aluminum solid so we used to this problem in 1 single step operated by 1 0 grams of aluminum deposited when I start with the and current Sino current isn't amperes times the time which was 24 hours I have to give this in seconds I'm going to convert 24 hours 2 seconds and all of
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this will come up to me that's a 24 hours per minute you know 60 minutes per hour and the 60 seconds for a minute so that would be the time so this is hereby multiply this by this it qualms and divide by various constant which is 9 . 6 5 times 10 to the book for Kulongoski promote so what I have got this gives me the number of molds of electrons right now I know that this is the number of moles electron in this equation can everybody CA that for every 1 mole of aluminum how many malls of electrons do need 3 OK so that means I can say for everyone mold of aluminum I need 3 moles of electrons all right so what I've got is molds of aluminum them so Kerry said that the 1st step was calculating the number of holes of electrons the number of moles of electrons I know that for every 3 malls electrons is 1 wall of aluminum now and then multiplied by the mall a massive of aluminum which is 26 . 9 8 grams GM from all and so what I end up with is 8 . 0 5 times 10 to the 5 grams of aluminum OK just to keep track of significant figures and since on using everything the 3 6 figs can you change this to 3 significant figures that your answer comes out of the significant figures sorry year and amperes to 6 figs this work out to say things if you make the Triassic things that gives
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you the grounds of aluminum that will be deposited right