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00:03Let me continue that balancing again, the redox reaction. This time we are going to treat the
00:12basic solution, not acidic solution. So we may focus on OH- rather than the proton H+. They
00:24are very similar to each other because, you know, we already have done all the processes for the acidic
00:31solution. Then that proton shows that solution could be acid, right? Then we can add the small
00:43amount of OH- to neutralize the proton. Then we just continue doing that until it becomes
00:53the basic solution. So let's take a look at the words here. A basic solution contains OH- rather than
01:03the proton and ions and water molecule. To balance the H atoms, we proceed as if in acidic solution
01:14and then add one OH- negative ion to both sides to neutralize that the proton concentration.
01:24That easy, right? For every OH- negative ion and H plus proton ion that appear on the same side
01:33and the equation we inform and that that might form the water molecule.
01:40So excess water molecules are cancelled in that in both sides. So we can remove all the water
01:49out from the skeleton equation. So excess water molecules are cancelled. That's the final step.
01:58Okay, so let's take a look at the problem. The permanganate ion reacts in basic solution with
02:05oxalate ion to form oxalate ion. This is oxalate. So this kind of like the it has a two acid
02:15form
02:16in in this case two carbon and both of the sides has the carboxylic acid this way. Oh, I'm sorry,
02:23OH.
02:24So they are going to take off from the molecule to make the acid side. But in this case, we
02:33do not have
02:34the acid. So it says like a oxalate anion rather than oxalate acid. So it's already gone. They are not
02:46existing. So the actual molecule should be O negative, O negative this way.
02:58So balance the skeleton ionic equation for the reaction between this one. So this is just a
03:05skeleton and it's not the balanced yet. So it also says basic solution, but we don't see any
03:13basic characteristics in this equation, correct? Okay, let's follow the process.
03:25Plan. We follow the numbered step as described in the text, as we did all for the same way
03:35with the acidic solution. So the first one, divide the reaction into half reaction.
03:41So let's take the calculation to the mass to figure out what's the oxidation number for
03:50mangan here. That's O4. It's a negative 2 times 4. That becomes negative 8. But we already have
04:00like a negative 1 here. That means it should be positive 7, right? That can neutralize.
04:06plus 7 minus 8. That makes negative 1, right? That's how you calculate the oxidation number
04:15for each element. On the right side, it doesn't have the formal charge for the molecule. It's 0.
04:230. So that's negative 2 times 2. That means it's negative positive 4. So it has been changed from
04:33positive 7 to positive 4. It has been what? Oxidized or reduced? Reduced. Because the number has been
04:43decreased. That's reduced. So what if we can use the words instead of reduced, just decreased or increased?
04:58That makes everything very simpler. But maybe they can deliver some wrong information for
05:08many things. I don't know yet. But we'll see. On the right side, I don't think the oxidation number for
05:17oxygen has been changed. So we will take a look at the carbon. And the formal charge for the whole
05:23molecule
05:24is 2 negative. But you know, oxygen is negative 2 times 4. And then C, we don't know. And then
05:32that's
05:332. Plus this should be 2 negative, right? So let's take a look at this. It's negative 8. And then
05:44so this should be positive 6. So that means this is positive 3. And then on the right side, we
05:55have
05:553 oxygen. That's negative 2 times 3. And that's negative 6. And we have negative 2 already there.
06:03So this carbon. So this carbon should have a positive 4. Correct? 3 to 4. It has been increased. That
06:16means it's oxidized.
06:17So simply it's oxidized. Reduced. Reduced. Reduced. Oxidized.
06:31That means this is the reducing agent. This is the oxidizing agent. Actually this molecule is
06:41the common oxidizing agent for many redox reactions. Okay. We just figured out the basic part.
06:53Then we see, we followed all the processes as we did before. Like left side, we have 4 oxygen,
07:02but on the right side, we have only 2. So we have to add some water molecule. And then
07:09to balance this, the hydrogen on the left side, we have to add like a proton, right? They will do
07:17the same
07:18thing on the left side and the right side. This is the reduced one. And this is oxidized one.
07:29Let's see. And then just we add, right? Like we have to add a charge to see how many electrons
07:41has been
07:42moved from the left side on the right side. That's what we have done. And then we multiply
07:49the integer number to balance the 3 electrons to 2 electrons. So on the right side, we will multiply 3,
07:57and then here 2 to remove that electron.
08:05See, this is the equation we are obtaining. But still it shows like acidic proton part.
08:15So we have to add here 4 OH negative. And then here 4, 4 OH negative. That's what we need
08:23to do.
08:24Then this will make what? 4H2O. And then we have 2H2O on the left side.
08:31So that will cancel out. And then the final one, 2H2O on the right side, right?
08:41So final equation is here. We have done so far. On the right side, we expected two water molecules.
08:49On the left side, we don't have any water molecule. Instead, we have the hydroxide, the anion.
08:58Because the whole solution is the basic solution. Okay? So that's how we can do things.
09:05The other way, you can just do some OH negative thing first. And then you can go back to acidic
09:14solution
09:14by adding the H plus, if you'd like to do that way. But you know, in that case, it has
09:22OH negative,
09:23O and the hydroxide. So it might not be easier to control the number of elements on both sides.
09:36So if you can do that easily, that's fine. So if we choose like a proton that only has like
09:44a H plus,
09:45H plus. So it's easy to balance the number of elements.
09:57Okay, that's the oxidation number. Based on that kind of information, we will go further for
10:03electrochemistry part. Electrochemistry is the area of chemistry concerned with the interconversion of
10:13chemical and electrical energy. Here, electrical energy. So we have to watch some electron movement
10:20from one side to the other or from one chemical to the other chemical. Okay? And in electrochemistry,
10:30chemistry, we have two terms, the galvanic cell or voltaic cell or electrolytic cell. The galvanic
10:39cell is like from, the words came from Galvani, who is like a scientist in Italy. He is an Italian
10:52scientist.
10:54Actually, he mainly focused on the bio part, bioenergy. His wife had been sick, and then the
11:07her family always prepared healthy potries. And then she had some frog soup, frog.
11:23So in the soup, it has, I'm sorry, I cannot draw the, this is a frog's leg.
11:37No, a lot of Koreans in old time, maybe 20 years ago, when I was young,
11:43then the, we didn't have that many things to eat. So we also caught a lot of frogs from the,
11:52the
11:53outside, the, around our neighbors. And then we, um, bake, bake them. Sometimes they like fry them.
12:06And then we ate those frogs. But Italy, they also had a same situation, but they also, they had some
12:15sort of
12:15like soup. And then the, the galvanic wife touched this leg with the metal, uh, chopsticks.
12:26And then the, the leg was like this. Then it has some sort of, what is that, like a joint.
12:38Then when she touched this part, or some, I don't know which part it could be exactly.
12:45And she touched some of this, like a part by the metal, the tweezers, not, I'm sorry, like a chopsticks.
12:55Then suddenly it moved. It moved.
13:02So she was very surprised. She felt like this egg, the frog is still alive.
13:09And then she mentioned that one to Galvani. And Galvani was thinking the every life science,
13:18every life, the life, the thing, they might have some life energy in their body.
13:25So this could be expressed that that kind of a life body. So he gave a talk about this,
13:33like a frog leg with, uh, frog legs, some, the life energy in the, in the conference.
13:42In that conference hall, the Volta was there. Volta was, Volta is also Italian researcher.
13:50He, he is a physicist, physics guy. Uh, and then the, he thought that's not from some life energy.
14:01It could be something else. So he tried to mimic the same, uh, situation with, uh, the metal contact.
14:10And then he finally found some, the electrical energy from the, the stack of metal with some electrolyte.
14:20So, uh, the, from that kind of anecdote, we call this, like a, the spontaneous, the chemical reaction.
14:33It generates an electron circuit that's called Galvanic cell, but also Voltaic cell.
14:41So, uh, so, uh, many people says like, uh, uh, the Voltaic cell instead of a carbonic cell because
14:48the carbon didn't invent the cell itself. But either way, uh, the, a lot of the general chemistry
14:59textbook mentions, like, carbonic cell rather than Voltaic cell. And then later on, the,
15:06the, they actually had, uh, the, the working, the, the battery system, that's Daniel's cell,
15:14so, later on. So, uh, when we say Galvanic cell, that means a spontaneous cell.
15:21Now we are not like a mentioning that Galvanic cell is, uh, consisting of some sort of design or
15:29something, but now like a Galvanic means a spontaneous. Okay. And then the electrolytic cell.
15:37Electrolytic cell is an electric current, which drives, uh, drives a non-spontaneous reaction.
15:44For example, let's say you have a, uh, cell phone that can be charged at night and then they can
15:53turn
15:53on the phone. We don't need to do anything. Just pressing the button is enough to turn on the,
15:59the cell phone. And then it shows all the display brightly and we can search something.
16:08The battery is working that way, right? Once we have the, uh, the closed system,
16:16the battery is, uh, the old time it's working. That's Galvanic cell because we don't do anything to
16:24let it work. We just turn on the device. That's it. Turning on the device is not like, uh, the
16:35irreversible the work we can do. So it's not, uh, I'm sorry. That's not a good expression, but you know
16:44what I'm saying, like, um, it can be on. We just intentionally turned it off, right? By disconnecting
16:52the, the, the circuit. Electrolytic cell means like, uh, the non-spontaneous. That means we can charge
17:00the battery at night by plugging in the electrical energy. So we add energy to, uh, refresh the, uh,
17:10the electron movement from the, from one side to the other.
17:22Okay. So the, I'm sorry. Electrolytic, that's basic. And then Galvanic cell, we mentioned that. And here's the,
17:32the Galvanic cell. That, uh, zinc, uh, copper ion goes to zinc ion and copper solid. The, do you remember
17:44that, uh,
17:45K-Ka-Nam-Ar-A-F-E-Ni, something, something? And the hydrogen, Kappa, silver, and then
18:00gold and, uh, beauty, something like this.
18:05On the left side, it has a higher tendency to be ionized.
18:10On the right side, it has a higher tendency to be reduced.
18:15So, they want to stay as is on the right side.
18:20On the left side, they want to be changed.
18:23We already know about that because see here, silver and gold and piti,
18:28they don't want to be oxidized. They want to stay as they are.
18:33That's why we kept them as a noble metal, right?
18:39What if these gold nanoparticles are easily oxidized?
18:47I don't know how many of you have the ring, the gold ring.
18:52We don't have any like the zinc ring or aluminum ring.
18:57Sometimes we do that for just accessories.
19:01But normally, we pay a lot of money for having the gold rings.
19:08So, let's say we have gold ring. Actually, I have one.
19:14When I wash my face, that makes a contact with water.
19:21What if they easily ionize, then they dissolve into the water.
19:29Then do you think we can keep those materials as a noble material?
19:36No. And also, that silver is also showing that kind of thing.
19:41That platinum is a very highly expensive, the noble metal too.
19:46And here, that proton H was written here.
19:52That's like a reference.
19:54Comparing to the proton or H element, we can simply see.
20:02So, they might not be easily oxidized in the water.
20:09Unless we do not have any proton in that water.
20:13Because this has been compared to this hydrogen reference.
20:20But whatever we say, on the left side, it has a higher tendency to be oxidized.
20:25They have a higher power to be oxidized.
20:28So, when we have two metals here, potassium and sodium.
20:35Potassium has a higher tendency to be oxidized rather than sodium.
20:41Okay.
20:42So, let's come back to the main material we are focusing on here.
20:50The zinc has been oxidized.
20:53Zinc two plus.
20:54And it generates two electrons.
20:57And copper ion.
20:59The copper ion accepts those two electrons and then becomes copper solid.
21:04You know, the zinc and copper, they are quite cheaper metals.
21:11That's why they could invent this kind of experiment in old time.
21:19Let's move on.
21:21So, this is actually the cell by Daniel.
21:27But here, they still mention that this could be like a galvanic cell.
21:33Actually, if we do not have this salt bridge.
21:37Then this reaction occurs for very short time.
21:41And then it stops.
21:43That's galvanic cell.
21:44And that's voltage cell.
21:46Once we have this salt bridge.
21:48That's moving the ion to balance the electron movement.
22:00So, this one is working.
22:03And then current battery devices are all made by this way.
22:09That's real Daniel cell or just a galvanic cell, whatever.
22:14Because the galvanic cell means like a spontaneous cell.
22:18Not indicating the original form of the cell.
22:24Okay.
22:24So, here zinc and copper ion.
22:28Let's take a look at how they set it up.
22:31Here are copper electrodes.
22:34Because we need two electrodes.
22:35They used copper and iron to see the copper deposition.
22:43Or the copper can be dissolved.
22:47And also, the zinc can be dissolved.
22:50Or zinc can be precipitated.
22:53Or coming out of the solution.
22:57Let's take a look at detail in the left side beaker.
23:01See, we have copper electrode.
23:06And then also copper ion in the solution.
23:10And then this copper ion accepts two electrons.
23:16Because zinc here, zinc donates two electrons.
23:19That's what we observed in the previous slide.
23:22Zinc donates two electrons here.
23:25It moves to the left side.
23:27And then brings to the copper.
23:31The copper electrode has many electrons on the surface.
23:35And then this can be jumped to the copper ion.
23:38Since copper ion can be located very close to the electrode.
23:43Although it has been drawn like this.
23:47Actually, the copper ion is very close to the electrode.
23:52It can accept those two electrons.
23:54And then make the copper metal on the surface.
24:03On the right side.
24:05So as we see here.
24:07Zinc can be easily oxidized into the solution.
24:12So zinc two plus can be going into the water.
24:18And two electrons are moving this way.
24:21But as you see.
24:23This ion has two plus the new ion species.
24:30That's not acceptable.
24:31Because the charge neutrality has been broken.
24:39Right?
24:41Electron has been moved through this line.
24:45So it doesn't stay in this solution.
24:49But two plus ion has been released to this solution.
24:55And also on the left side.
24:58Copper two plus ion has been removed from the solution.
25:02So on the left side.
25:04We still need more positive ion.
25:08On the right side.
25:09We need negative ion to balance this one.
25:13So that's what this salt bridge is doing.
25:17Salt bridge has a lot of ion compound inside.
25:20On the right side.
25:21So on the right side.
25:24We need negative ion.
25:26So negative ion goes to the right side.
25:29And then on the left side.
25:31The copper plus ion has been removed.
25:34So we add more sodium ion on the left side.
25:39When we make this salt bridge.
25:42We have to be very careful.
25:43Because if some ion.
25:47Which can be easily oxidized.
25:51Or reduced.
25:53Before the material of interest.
25:56We are focusing on.
25:58Then this ion may be participating in that reaction.
26:05But sodium is not easily reduced.
26:09So see.
26:11Do you remember that?
26:18This one is oxidized.
26:21And copper is located here.
26:23And then sodium is here.
26:26Sodium ion, calcium ion, and potassium ion.
26:29They are easily oxidized.
26:31They don't want to be reduced.
26:35See.
26:35That's why they are using sodium and sodium ion.
26:38because sodium chloride is quite easily obtainable. It's very easy to use.
26:45So a lot of people are using sodium chloride or salt, very salty salt.
26:53That can be easily used for the electrolyte.
26:59Okay, I hope you understood the things.
27:02Then in the previous slide, we just call that electrode as a kappa electrode or zinc electrode or something.
27:10But actually we have to call them in this term, like anode.
27:16Anode means oxidation occurs.
27:20And also the cathode means reduction occurs.
27:28A, O, A, O, C, R, C, R.
27:36Then the oxidation occurs.
27:39That means something has been oxidized.
27:46For example, carbon plus oxygen and CO2, right?
27:52If this reaction occurs in that part, that's the anode.
28:01So this could be anode.
28:03That's electrode, carbon electrode.
28:06And cathode, reduction occurs.
28:09Something should be reduced.
28:12Reduction, that's sodium plus electron becomes sodium.
28:18Something like this.
28:20That's cathode.
28:22I think you already know about this.
28:24The Korean words are very complicated.
28:28I don't know which one is 양극 and which one is 응극.
28:32But in English, cathode and anode.
28:35They are using only cathode and anode.
28:37And also the word itself is defined as this one.
28:43So just take a look at the electrode, what's happening.
28:46And then if the oxidation occurs, that's always anode.
28:50If reduction occurs, that's always cathode.
28:53But in Korean words, like 양극, 음극, it's changing, right?
28:58Because the 양극, 음극 has been defined as the spontaneous device.
29:09So if they are not spontaneous, that actual term should be changed.
29:16But we are using the same term for both.
29:22So for example, in English, that galvanic cell, that in here, if this one occurs, that zinc is oxidized, this
29:39one is anode.
29:41But when we apply the voltage, maybe the other reaction may occur.
29:46But in that time, that becomes cathode.
29:51Their name should be changed depending on the definition.
29:55But in Korean, we don't change the electrode name.
30:01We just show the position of that electrode.
30:07So we observed that anode reaction this way.
30:12And cathode reaction this way.
30:14Accepts the electron, donates the electron.
30:17That's what we have done.
30:19Overall, scatulon reaction.
30:21That is also called like 알자 반응식 in Korean.
30:28But that has been written in many textbooks.
30:31So that's why I'm saying that way.
30:34But actually, skeleton ion reaction.
30:41Here is some short-handed notation for galvanic cell.
30:45We observed that something has been oxidized.
30:47Something has been reduced.
30:49And also, we have some salt bridge.
30:52See, in the salt bridge, we have like two lines here.
30:56And then on the left side, anode.
30:58And on the right side, cathode.
31:00So in the anode, see anode, it generates electron.
31:05So actually, electron is generated on the left side.
31:09That has been moved to the right side.
31:11And electron flow.
31:14But here, we have another line here.
31:17And that line is showing some phase boundary.
31:24Solid and aqueous.
31:26Most likely, this has been oxidized.
31:29And this has been reduced.
31:32So we can see this way easily.
31:35Right?
31:37And also, we are looking at the same thing.
31:41But what if we have Zinc 1+, and 2+, they are all aqueous form.
31:49Then sometimes, they just put the comma.
31:54Because they have the same phase.
31:57But still, we have to have some electrode for that reaction.
32:01Right?
32:02So that electrode still needs to be written.
32:05So here, Zinc 1+, and Zinc 1+.
32:08That's just the example.
32:10I don't see there is any Zinc 1+, at all.
32:16Okay, I will continue for the next recording soon.
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