Hello guys, good evening, can you hear me? Yes, sir. So I think last class, we were discussing about the classification of collides, right? And we discussed lyophilic and lyophobic collides, I guess. Yes, is it? Lyophilic and lyophobic, we have discussed. OK, so next, the classification we have, that is based on the type of particles of the dispersed phase. OK, basically size of the particles, right? Different types of the particles, OK? Yeah, so we'll start now. So next, one of you write down. Classification of the second type of classification. Classification based on the type of particles dispersed phase of dispersed phase. OK, so based on this, basically, we have three types of collides. One is multi-molecular collides, macro-molecular collides, and associated collides. OK, I'll write down this one by one just a second. Write down the first type in this we have. Multi-molecular, write down. See, basically, I'll tell you what happens in all these. This one and the next one, that is macro-molecular collides, are very much similar, OK? But the type, the type we can say or the way by which the dispersed phase particle we get into this, that is the only different thing we have. In multi-molecular, what happens? We have very small size particles, which aggregates. And finally, their size falls in the range of the size which is required for a mixture to be colloidal mixture, OK? So this size, which falls in the range of colloidal mixture, this we get by the aggregation of particles, by the combination of particles. But in macro-molecular, which is the next type we have, in this we have exactly opposite. In macro-molecular, we have bigger size particle, that dissociates, and finally, the size of the particles falls in the colloidal range, OK? So multi-molecular, what happens? On dissolution of large number of atoms of molecule, large number of atoms, molecules of a substance, of a substance. So in the mixture, in the mixture, whatever it is, atoms or molecules, so let's say molecules, aggregates, molecules aggregates to form a species, to form the species having size, having size in the colloidal range. And when the size in this range, the mixture is said to be colloidal mixture, right? Like you see, we have an example of sulfur-soul, OK? So example right down. In sulfur-soul, what happens? We have S8 molecules present, number of S8 molecules, sulfur-soul. We have S8 molecules present, which held together by Van der Waal forces, OK? Size falls in the colloidal range and held together by Van der Waal force. Just we have definition, nothing much in this. So overall, the objective is what the size must be in colloidal range for a mixture to be colloidal mixture. So either aggregation or by dissociation, both ways it is possible, right? If larger size molecule we have, it will dissociate and will get the size, which is in the range of colloidal mixture. If smaller size molecule we have, it aggregates and finally the size becomes in the colloidal range. So multi-molecular is a case of aggregation when the molecule combines, atoms combines. The second type we have, which is macromolecular colloids, right down the definition, macromolecular colloids, right down. In this type of colloids, in this type of colloids, large molecular mass, in this type of colloids, large molecular mass are dissolved in a suitable liquid, dissolved in suitable liquid. They form a solution in which the size of dispersed particles, size of dispersed particles falls in colloidal range. Size of dispersed particle falls in colloidal range. The example of this type of colloids is when we have polymers, OK? Polymers basically involve in this. So example right now, like naturally occurring macromolecules, we have starch, cellulose, proteins, enzymes. So all these molecules, colloidal solution that we have, they fall in this range, macromolecular colloids. So could you repeat the first line of the definition? First line of this one? Yes, sir. The definition, right? I said in this type of colloids, in this type of colloids, large molecular mass are dissolved into a suitable liquid. This is what I said, I guess. Yes, sir. OK, large molecular mass are dissolved into suitable liquid. OK, so here we are. A solution you have written, solution is, sorry, example is we can have colloids of starch, cellulose. All these are naturally occurring, right? Similarly, we can have man-made also, like polythene, synthetic rubber, polystyrene. All these polymers, the colloid's forms falls in this range, that is, macromolecular colloids. Now the third type of, one second. Now the third type of, we should be aware of that. Just a second, guys. Yeah, the third type we have in this, we call it as associated colloids, OK? Out of these three, the third one is the relatively more important, right? The third type you write down next page and go. We have associated colloids. In this type, what happens? See, there are some substance, when the concentration of these kind of substance is low, the solution or the mixture that you have, these mixtures behaves as the normal electrolytes, OK? But if you keep on increasing the concentration, right, after a certain concentration, it takes the colloidal properties, OK, colloidal behavior, due to, again, the formation of aggregates. So the difference from the previous one is what? It has the property of electrolytes initially, and then after a certain concentration, it gains the property of colloids, OK? This kind of colloids, we call it as associated colloids, OK? Associated colloids, also known as, you must have heard the name. It is missiles, M-I-C-E, double L-E-S missiles, right now the definition. There are some substance, there are some substance which behaves as normal electrolytes, normal electrolytes at low concentration, normal electrolytes at low concentration, next slide, write down. As we keep on increasing the concentration, as we keep on increasing the concentration, it gains the colloidal properties, it gains the colloidal properties, right? It gains the colloidal properties, OK? One more term we have in this which, you know, they have asked this question in need many times. See, when I say that there's a certain concentration, minimum value of concentration, beyond which it starts behaving as a colloid, which is also called as missiles, right? So this minimum temperature that we have, this minimum temperature, we call it as craft temperature, sorry, we call it as critical missile concentration, and the temperature at which this thing happens, we call it as craft temperature, OK? So write down next line into this. The formation of missiles, write down. The formation of missiles, of missiles, takes place, takes place above a particular temperature, above a particular temperature, a particular concentration, particular concentration. So the minimum concentration that we have, at which the formation of missile starts, this temperature, minimum concentration, we call it as critical missile concentration, CMC in short, we call it as, right? CMC, critical missile concentration. The temperature, minimum temperature, which is required here, we call it as craft temperature, represented by Tk. Just this definition you need to memorize, nothing much. So what happens in this, you have, you know, you have that colloidal solution, when you dilute it, right? It has this property that upon dilution, it again starts behaving as the electrolyte, OK? So initially you have, suppose some liquid, once you start adding particles into this liquid, the particles will get, you know, dissociates and behaving as an electrolyte, initial, correct? Amount is fixed, so we will have a certain point, certain concentration beyond which there will be aggregation of ions and finally it converts into collides, OK? When the, again, when the particle size falls in that particular range. So for this volume of liquid, that is the critical missile concentration and obviously we have certain temperatures, right? When you keep on diluting it, keep on adding water or any liquid into this, then again, the aggregates that we have over here, this again dissociates and starts behaving as an electrolyte again. So obviously for this amount, you have certain amount you have added, for that the graph temperature will also change, critical missile concentration will also change and if you reach this particular point, then again it starts behaving as a associated collides, OK? See the best example of this kind of collides we have, example we have soap solution, soap we can say, we can say detergent and water solution that we have. All these are the example of, you know, associated collides, OK? Soap, if you see here, soap is the sodium or potassium salt, write down, sodium or potassium salt of higher fatty acids, salts of higher fatty acids. So basically it has two components in the soap, we have two components, one is the chain, alkyne chain and then we have the carboxylate ion, COO minus and we can either take sodium cation or potassium cation, OK? This is the, I'm not saying this is the exact, you know, the formula of soap, right? We also call sodium cation or potassium cation, right? It is not the exact formula, I'm just giving an example and instead I'll write down like this, I'll give you the specific, in general formula in a better way. We'll take instead of this alkyl group, I'll write down here R, in general, right? RCO, O minus NA plus, OK? Now this R group actually it has two components, right? It is the anionic part and the cationic part. So when you dissolve this in water, what happens? This dissociates RC double bond O, O minus and NA plus it forms. So our focus is on this, only this, right? So let's see this, what happens? Suppose we have a random example I'm taking, this is the alkyl group we have and this is the carboxylate ion, carboxylate ion, OK? Now this you see, this is the anion of the soap particle. It has two end, one is, this end is water lover, right? So this is hydrophilic head, we call it as. This is hydrophilic head. And this entire part, the chain, the carbon chain that you have, the carbon chain is a hydrophobic tail, right? This carbon chain is the hydrophobic tail, right? Right, hydrophilic head, hydrophobic tail, correct? So this is water repellent, this is water lover, right? So when you dissolve this in water, this end is towards the water and this hydrophobic part is away from water initially, correct, away from water initially. So what happens, if you keep on adding the soap or detergent into water, if you will reach the critical missile concentration CMC and in that particular concentration, it behaves as a colloidal solution and at this concentration what happens, the hydrophilic head is obviously towards the water and this is away from water. So what happens? It will drag into the bulk of the liquid, right? The tail that you have hydrophobic tail, it drags into the bulk of the liquid. If you look at the initial situation that we have, I'll just know. Sometimes on this particular thing, they ask questions, the mechanism, how soap works actually. So some theoretical questions they can frame on, that's why I'm discussing this. So initially it was like, suppose we have this container and in this water is present, this is the surface of water we have as you, right? So this end hydrophilic end is into the water, right? So assume this is the hydrophilic end we have, hydrophilic end into the water and this is the tail we have, hydrophobic tail away from water, like this it was, okay? At critical missile concentration, this starts getting attracted and this is pulled into the bulk of the solution and it aggregates to form a spherical shape, right on this point. At critical missile concentration, CMC I'll write down in short, at CMC the anions are pulled into the bulk, bulk of the liquid and forms spherical shape with hydrocarbon chain pointing towards carbon chain, pointing towards the center of the sphere, towards the center of the sphere. So we'll have this CO minus outward, okay? We have a circular thing, CO minus will be outward. This happens at critical missile concentration. So this is what happens with the dirt or the oil droplets that you have. So whatever the oil droplets or the oil droplets so whatever the oil droplets or dirt that you have, it forms missiles around this oil droplet. So the hydrophilic part will be into this oil droplet. For example, you see it is like this, hydrophilic part is like this, right? So hydrophilic part is away and the tail you have, it is towards the dirt or the oil droplets. This is the oil droplets we have, so it forms basically a bond between the oil droplets. So all these negative charge you see it is aggregating over here. Negative charge is aggregated over here. So around this you see the negative charge density is increasing, right? All these negative charge particles are repelling each other in all direction. These particles are repelling each other in all direction, right? And then what happens this oil droplets, it breaks down into small, small pieces and forms the colloidal solution in the mixture, correct? Which can easily wash away with the flow of water and hence the dirt or whatever oil particles we have removed from the surface of the clothes we have. And that's at this point, the working. What I said in the last that whenever you have dirt particles or oil droplets, right this soap particle that you have, it forms, it forms what? It forms missile around the oil droplets. This is the missile we have. In this missile, what happens? The tail is towards the oil droplets and head, the anionic head is away from it. So all these tails is getting attracted towards this. There are a lot of negative charge ion present around it which repels each other and hence this oil droplets dissociates into small pieces because it will go away because of repulsion, all the soap particles will go away. So it will go away with the oil droplets also into the pieces, oil droplets will be in the pieces. So when you wash with water, it will remove from the clothes. That is how the soap works, correct? This is the three types of colloids we have on the basis of the size of the dispersed phase particles present into this. Now, how do we prepare this colloidal solution? See, lyophilic is water-loving. So water-loving is very easy to prepare. You just mix dispersed phase and dispersion medium mix. You'll get lyophilic because both are attracting, no? So next to write down, but for lyophobic, we have certain methods that we use to prepare, okay? Lyophobic will see few methods, not that important, but one particular preparation method that we have, that is important, our entire focus will be on that only, okay? That is peptidization we will see. So write down the next point, preparation of colloidal solutions, preparation of lyophilic soil, lyophilic soil, write down. It can be prepared by the mixing of a substance, mixing of a substance with the dispersion medium directly. So could you repeat the first thing again? I said lyophilic soil can be prepared by mixing of a substance with a dispersion medium directly. Miss dispersion medium you have, you mix the substance into that. You'll get the lyophilic soil, because lyophilic soil is water-loving, right? It attracts water. So you don't have to put any extra effort into this, right? Directly you will get it. So that is the preparation method. So that is the preparation method here. So for example, you see, if you want to prepare the colloidal soil of starch, gum, et cetera. So what we do, we'll take this starch and we dissolve this in the water, basically warm water we'll take and we'll get the lyophilic soil. Similarly, if you want to prepare the cellulose nitrate, then we simply dissolve the organic, like the cellulose we have into any organic solvent like ethyl alcohol we can use. So we can use alcohols or some organic solvent also in order to prepare the colloidal soil, correct? That's one thing. One more term we use over here, you see, like if we use cellulose nitrate, and we dissolve this into organic solvent, mostly organic solvent if you use, like for example, we are using alcohol, right? Alcohol we use. So this kind of soil that we get, this kind of soil, we use a specific term here. We call it as colloidal, CO-D-I-O-H. Organic solvent we are using for preparation of this colloidal, okay? Now, easily you can understand the second one that is lyophobic, lyophobic soil. Lyophobic soil you see, it is water repellent. So we cannot mix the two substances and we can get the solution because the dispersed phase will repel the dispersion medium. So it is not that easy to form. So we have to have a specific methods in order to obtain lyophobic soil, okay? Now, since it is water repellent, so we could use some substance which works as a stabilizer in order to stabilize the soil, right? So in this particular thing, we also use some stabilizers to stabilize the soil over here. So what are the different methods we have by which we can prepare lyophobic soil? So just one line you write over here that we use different methods in order to prepare lyophobic soil since it is water repellent, okay? We use different methods in order to prepare lyophobic soil since it is water repellent, okay? So basically we have two major two methods we have by which we can prepare. I'll write down here only. Basically we have two methods. One is dispersion method. Dispersion method, I'm just giving you this name here. And the second one is condensation method. Dispersion and condensation method, right? Dispersion method, again, we have three types that you'll see after this next slide. Condensation method generally we use. In this also we have different, different ways. We can exchange solvent and we can get this kind of products, right? Like NaCl and AgNO3, right? Double decomposition react. They may also follow this kind of products, correct? So condensation method is not that useful. Dispersion method we are going to use. In this we have one or two methods in which total we have three methods, but two methods they'll ask question. Condensation is not that important. So we're not doing all these things, right? So dispersion method we have three types, like I said. The first one is this of integration which is nothing but mechanical disintegration. Mechanical disintegration. This comes under dispersion method, disintegration, right? Mechanical disintegration is the method comes under dispersion method or dispersion method we also call it as disintegration method. It's also the same thing. Disintegration method or dispersion method are the same thing, correct? Mechanical disintegration. What is mechanical disintegration? We just reduce the size of the particles into the colloidal range by some mechanical method, okay? So what we do, we have, we use a machine here we call this colloidal mill. In colloidal mill, what happens? There are two disks, okay? If I show you the diagram here, we have two disks into this, like, and there is some space, some gap in this two disks. If you try to understand this, 3D, if you understand, this part is going into the screen and this part is coming out of the screen. So we have two disks like this, we have some space between the two, right? And we allow the dispersed particle, that is dispersed phase to pass into this disk. And the both disks are rotating in different direction. One is going clockwise, so other one is going anti-clockwise like that, okay? Like this, different direction. So when you allow this dispersed particle, phase particle to pass through it, obviously the rotation is in two different directions. So they'll crush the particles into small pieces, right? Basically, they are reducing the size of the particle and first of all, we'll reduce the size, we'll mix liquid into this and then again, we allow this pass through for the colloidal mill, okay? And hence we'll get the, what we say, lyophobic, so write down in this thing, what do you think? There's two, three points to write down. It is carried out in a machine called colloidal mill, colloid mill, colloid mill or colloidal mill, both we can say. It is carried out in a machine called colloid mill, write down the solid material, the solid material is allowed to pass through the colloid mill, which reduces the size, which reduces the size. Then it is mixed with dispersion medium, then it is mixed into the dispersion medium, which forms a coarse suspension, C O A R S E, which forms a coarse suspension, right? This suspension is again introduced into the colloidal mill. This suspension is again introduced into the colloid mill. The particles are ground down, are reduced, write it like this, the particles are reduced to the colloidal size. The particles are reduced into the colloidal size. Next time, A stabilizer is often added to stabilize the colloidal solution, right? A stabilizer is generally, which stabilizes the colloid. It's generally added to stabilize the colloid. In is one of the example of stabilizer, TANIN, P A double N, I N, TANIN, one kind of biomolecules substance here, okay? TANIN is an example of a stabilizer. TANIN is one of the example of this kind of substance. We used to prepare printing ink by this method, mechanical disintegration. So this is mechanical disintegration, where we are using the machine called colloidal mill, right? Second method we have for the preparation of this type of collides, lyophobic collides is, we call it as electrical disintegration, mechanical. And here we have electrical disintegration, mechanical and electrical disintegration. So electrical disintegration, this method, we also call it as Bredix arc method. B-R-E-D-I-G-S, Bredix arc method. More important than the previous one, as far as exam is concerned, okay? This is used for the, for obtaining a colloidal solution of metals, okay? Write down like this. Used for obtaining the colloidal solution of metals. Metals like, you can have gold, silver, Latino, this kind of metal here. Write down the method here. In this method, in this method, an electric arc, in this method, an electric arc is struck between two metallic electrodes. I'm repeating in this method, an electric arc is struck between two metallic electrodes, between the two metallic electrodes, immersed in the dispersion medium. Both electrodes are immersed in dispersion medium. What an electric arc? Electric arc is struck in, struck not in between, struck between two metallic electrodes, immersed in the dispersion medium. Now, so since we are giving this electric arc, some of the metal, because we have metal electrodes, some of the metal, because of the high heat, it vaporizes, right? It vaporizes, and then it get condensed into the dispersion medium, and hence the colloidal solution forms. So from metal, we are, you know, we are vaporizing the metal atoms by providing electric arc into this, which vaporizes and then condense back into the dispersion medium, and we'll get the colloidal solution, right? This is what it happens. The stabilizer that we use here, right? That is KOH, potassium hydroxide we use. This question they have asked. In Bredick's arc method, right? The KOH is the electrolyte, sorry, stabilizer that we use. So only this is thing they have asked was KOH, okay? Or Bredick's arc method used for obtaining colloidal solution of metals. These two things you must remember. Now the third type of, you know, method we have to prepare colloidal solution is peptidization. So is this under dispersion method only, or is it? Yeah, it's under dispersion only. Disintegration, dispersion, whatever it is. Three types we have under dispersion, peptidation. So what is peptidation? Peptidation is actually defined as the process of converting a precipitate into colloidal solution, okay? So we are converting a precipitate, and this is what we were discussing last class also in last precipitate is converting into colloidal solution. So which one that like ATIM and ATU surround that? Ha ha ha, correct, same thing. Right now in this process, and electrolyte, one second. In this process, an electrolyte is also added, which is called peptizing agent, peptizing agent. Usually this peptizing agent contains a common ion, usually in general. Generally it contains, it contains a common ion, not true always, it is not required, it's not like contains a common ion. It is not like it is always required. But in general, we used to select the peptizing agent like this one, contains a common ion. Sorry, your voice is not coming as the, not at all. If you're using headphone, earphone, plug it again. Yeah, I said peptizing agent, generally it contains a common ion, right? We add a small amount of electrolyte in this, which we call it as peptizing agent. We add a small amount of electrolyte into this, which is called peptizing agent. Peptizing agent generally contains a common ion. Example you this, see this, a reddish brown colored colloidal solution, a reddish brown colored, reddish brown colored, colloidal solution, colloidal solution is obtained by adding, is obtained by adding a small quantity of, quantity of FECL3 solution, FECL3 solution to FEOH whole trace. So like I discussed last class, during peptization, what happens? Suppose we have, first of all, you copy down this, I'll go to the next slide. Suppose we have a solution of AGCL, correct? Basically precipitate, we have AGCL, somehow the precipitate forms. And in this, if you add AGNO3, AGNO3. So what happens, the precipitate of AGCL, the precipitate of AGCL, it absorbs ADM talking about. It absorbs AG plus on its surface like this. All this positive charge are AD plus, so the AD plus here. It absorbs at the surface of this, right? So all these positive charge are present very close to each other. Because of repulsion, it dissociates finally, means this particular electrolyte that you have, means precipitate that you have, it dissociates into the smaller particles of colloidal range because of the positive charge present here. Positive charge will be there, but it dissociates in colloidal range. So when we say it dissociates into smaller particles, what are the smaller particles? See, any, we have any atom, we don't have the molecules or atoms of it. AGCL you have. So this will reduce the size, means you have a lump of this, whatever precipitate we have crystal of this, no AGCL. So this AGCL crystal only, it will dissociate into smaller pieces. Okay, sir, yes. And each will have that positive charge on it. Yes, sir, go on. Correct. So it's the thing that the smaller pieces will fall into the range of colloids and hence it behaves as a colloidal solution. So how do we like, you know, control it so that it doesn't dissociate even further? See, everything is, we don't have any control over here. Frankly, if I tell you why it dissociates because of the accumulation of charge on it. Okay, a lot of charge will be there. So a lot of repulsion, positive, positive repulsion will be there. And results to this, it will dissociate into the smaller particles, right? What we do here, if the, what we observe actually, if the size is small, then the particle, you know, will be in the colloidal range, right? It will have the property of collides. Further dissociation also possible if you put, if you, you know, give more amount of charge on this particle. But what we have observed that with the smaller size, positive charge on this, the density of positive charge is not that great as we compare over here, here and here, correct? So that charge is not great enough that the repulsion over there is not great enough to dissociate this particle. And that's how it happens. And it is a stable then, size is stable then. In some book, they haven't said that it dissociates into smaller particles. It is not always true. Like if the particle size is not big enough, then it will only take the positive charge on it, right? And it will move into the solution from one point to other point. You see this ADCL with this positive charge, it looks like this. And it will continuously move. It won't settle down the charge over here, right? So whether it dissociates or not, it is, you know, not in our hand, basically, it dissociates because of the repulsion of the positive charge. And when it becomes stable, it will move and consist the property of collides. That is it. Yeah? Yeah, sir. So this is one way, actually. This is one way. It's not like, like I said, that questions that you get in JEE, they have asked question on this. The questions that you get in JEE, usually they, you know, ask you questions of common ions over here. Means you have ADCL precipitated, and if you want to form a colloid of this, you will add an electrolyte into this, peptizing agent. And this electrolyte must use the question that they gave, I'm talking about. They will give this, must contain a common ion, AD or CL, anyone you can take. So AD plus is the common ion. But I'm saying it is not the only way to obtain the colloidal solution. We can always, we can also add some organic solvent into this, right? Now the difference in the two is what I'll tell you, because we are going to study now this portion from this only they asked question in the exam. We are going to study about now the charge on the colloidal solution. If you remember last class, you know, towards the end of the class I told you that colloidal solutions are stable due to what? Due to? Repulsion. Repulsion, right? So repulsion will be there when we have either positive charge, only positive charge or only negative charge. So we can say any colloidal solution will be either positively charged or negatively charged. Yes, both kind of charge won't be there in the colloid. Otherwise it will neutralize and settling will be there. It won't be a colloidal solution, correct? So both kind of charge won't be there. Either it will be only positive or only negative. So you should know this particular information that which soul is positively charged and which soul is negatively charged. Are you getting it? Right, so how do you know this? Once you have this kind of combination, you see, like I said, AGCl is the precipitate and AGNO3 you are adding. So we have observed, this is the fact we have, that this precipitate, it absorbs generally the common ion on the surface. So we are adding AGNO3, so we have only one choice that AG plus will get adsorbed on the surface. And when this happens, the colloidal solution is what? It is positively charged. So in this kind of combination is there, you can identify whether the soul is positively charged or negatively charged. Suppose we have AGi, silver iodide precipitate and we are adding Ki into this. Then what is the charge on the soul? It's negative charge. Yes? I minus negative charge. Negative charge, because the common ion is what? Here you see, common ion is I minus. So this I minus will get adsorbed on the surface and it provides the negative charge to the soul. Isn't it? So in this kind of combination is there, common ion concept is there, then you can identify, you can understand that what would be the charge on the soul, right? But it is not the only way to prepare colloidal solution. Like I said, we can also add some organic solvents. So in that case, you should know, you should memorize the charge on the soul. I'll give you some examples of charge on the soul. But that you need to memorize. Now, this is the one thing, the preparation of soul. One note in this, you write down. Peptidation can also be achieved by, peptidation can also be achieved by organic solvents. By organic solvents. Example, few minutes back I've given you, cellulose nitrate with ethanol. Ethanol is the organic solvent. Cellulose nitrate with ethanol. So we'll talk about this stability of collides now, and then we'll see the properties, the last points we are going to discuss here. Okay. You see, one point to write down next, or the heading you write down. Charge on the soul. We don't have much example here. For five we have that you need to memorize. Charge on the soul. The soul can be positively or negatively charged. The soul can be positively or negatively charged. So the examples of positive charged soul, positive charged soul, we have all hydrated metal oxides. Hydrated metal oxides are positive charged soul. Example you see, FE2O3.XH2O. Just this charge information you should know. Why it is important, I will tell you one more concept we will discuss, that is coagulation. How coagulation is possible and how we can protect the soul, that information you will have once you know the charge on the soul. FE2O3.XH2O, or we have other metal oxides, CR2O3.XH2O, for example, 2H2O, XH2O2. Hydrated it is. Human blood. Human blood is also a type of colloidal solution. Human blood. You must have heard the term dialysis, right? What is dialysis? What we do in dialysis? When kidney fails, mechanically they purify the blood. Purify the blood, right? The impurities will try to extract from the blood, isn't it? Yeah, right. So kidney is used to purify the blood basically. So we will discuss this particular dialysis also in the last, the use of the colloidal soul. So blood is a colloidal soul, positive charge colloidal soul we have, okay? In the soul, we'll have some impurities also. Every soul will have some impurities. So we need to remove that impurities, otherwise it led to coagulation of soul. Coagulation means it will lose its colloidal property. Correct. Because repulsion won't be there, it is not stable there. The particle will settle down. How coagulation? Coagulation is nothing but aggregation, flocculation, right? When the particles combines, okay, the small soul particles are there, particles combines, the size will increase, gravitational attraction will be more and the particle settle sounds, it loses the colloidal property, right? So coagulation you can achieve when you destroy the charge on the soul, yes or no? Because like I said, the colloidal soul are stable because of repulsion, correct? Once you destroy the charge, then there will be no repulsion. No repulsion means the particle will settle down and hence it will lose the colloidal property, correct? Got it, guys? Yes, sir. Yeah, so the thing is coagulation or flocculation, right? We can achieve in two, three different ways, okay? By adding some impurities, even the electrolyte which is present there in the colloidal solution, we must have a requisite concentration of electrolyte. If you have the concentration of electrolyte more in the solution, it also leads to coagulation. So for any colloidal solution at any temperature, we must have a requisite amount of electrolyte present into this. More amount of electrolyte also leads to coagulation, correct? So we also need to maintain the concentration of electrolyte present in the colloidal solution. If it is more, we have to remove them. So basically more amount of electrolyte is the, what is the impurities? It behaves as an impurities. Similarly in blood also we'll have some impurities, right? And we used to remove the impurities with the help of some membranes, okay? That we use in osmosis also, right? What is that term we call it as? Semi-permeable membrane. Semi-permeable membrane. Similar kind of thing also we have here, right? So to purify blood, the function is done by, now we know the work is done by kidney. So if the kidney is not working properly, so we need to do it from the outside, right? We use that device to purify the blood in order to remove the impurities which is present in the blood. We do dialysis, right? So we'll have the membrane from which membrane, electrolytes particles can pass through, colloidal particles does not pass through. So these impurities passes through the membrane and we'll separate it. We'll get the pure thing, but also we'll get pure. But blood also will get pure. But again, you have to remove this impurities continuously. In dialysis, we have to clear the membrane after some time. Otherwise, again, when the other side of the membrane, if the impurities concentration will rise, it can again go back into the blood. So that will again cause damage over there. So that's the process of dialysis we have. Dialysis works on this thing only, right? Because human blood is also an example of a positive colloidal solution, okay? So this is the second example we have. Solution of TiO2 is also an example of positive charge soul. The charge is very important. You should know that charge on the soul, correct? If you get some other examples also, you just write it down and mug it up, okay? There's no other way. You have to memorize the charge on this. Negative charge soul, negative charge soul. Let me just check any other example we have. Oxides of TiO2, we have some more examples. I'll write it down, wait a minute. Hydrogen metallic salts we have in written. Basic diastox, okay, this is the term written. Basic diastox. So we don't have much example over here. Three, four, five examples we have that you need to keep in mind. Okay, like methylene blue soul. In this only it is methylene blue soul. Example of basic diastox. All these are positively charged soul. Negative charge soul, we have the example. All metal soul that we have, copper soul, right? Silver soul, gold soul, all are negative charge soul. Metal souls, gold, copper, silver, all these are negative charge soul. Metallic sulfides, metallic sulfides are also negative charge soul, AG2S3, CDS, right? AS, SB2S3, sulfides are negative charge soul. Here we have basic diastox. So here we have acidic diastox. Diastox are negative charge soul. Souls of starch, gum, charcoal, gelatin, et cetera, are negative charge soul. Okay, we know the reason of this charge. That is the adsorption of common ion. Okay, we have other reasons also given, but this one that I have told you, the adsorption of common ion in general is the most accepted reason one, right? Why the soul has this kind of charges, okay? Now, the positive charge soul of AGCL, we used to write like this, AGCL, right? And we have AG plus like this. This is the positive charge soul, AG plus surrounded this AGCL. If you have AGi is surrounded by i minus, we used to write this as the negative charge soul. Negative charged soul. So you must understand how to write this. Is the positive charge soul. Okay, this is one thing. One more example you write down to this. FECL3 is added to excess of hot water. A positive charged soul of hydrated ferric oxide forms. FE2O3.xH2O, a positive charged soul of hydrated ferric oxide forms. FE3 plus get adsorbed on the surface. We'll get a positive charged soul. Okay, so this is the positive charge soul of AGCL. This is the positive charge soul of AGCL. This is the positive charge soul of AGCL. We'll get a positive charged soul. However, we have FECL3 ferric chloride. And if you add NaOH on this, sodium hydroxide. See, we are adding water here, excess of hot water. Excess of hot water we have. And here we have NaOH, right? NaOH, if you add into this, NaOH to FECL3. So if you have FECL3, we have added to this. So it forms ferric oxide. So we have this. In this, what we get? We get a negative charged soul, which is other way. We are having NaOH. And in NaOH, we are adding this FECL3. Okay, so in this also, we get an hydrated ferric oxide, which is FE2O3.xH2O. But it is a negative charged soul surrounded by OH-IM. Because if this OH-IM is present over here, FECL3 we are adding to it. So negative charged soul it forms. Now in this only, we have one more term. Like for example, you see, we have AGI, right? AGI, like this, the precipitate we have. And all these precipitate, we know it is surrounded by the common ion, which is IE-, right? So we'll write down IE- just next to it. IE- IE- I'm taking this example. It depends what you are adding into it. AGI NO3 you are adding, or KI you are adding. If you add KI, negatively charged. If you add AGI NO3, positively charged. I'm just taking an example of negative charged electrode, right? So we have this. Now in this, we got a layer like this. We have AGI and then IE- above it, like next to it. So this layer, we call it as fixed layer. This layer that we have, one after this, it is fixed layer. And since we have IE- present here, so very next to it, very next to it, we have K plus present here. See this? Very next to IE- we have K plus present here. K plus, because we have positive negative attraction, so K plus will be nearby only. But this is not very strongly attracted, right? It is just movable, right? K plus can move here and there. So this layer that we have here, we call it as mobile layer. All these are observations we have. Okay. Mobile layer. K plus can move here and there. Right? So we have two layer here with different charges. So obviously we'll have the potential, you know, developed between the two layer, between these two layer. This potential, we call it as zeta potential. So here I done. The potential developed because of the two opposite charge. The potential developed is called zeta potential. Zeta potential. Another name of the same word, zeta potential is electrokinetic potential. Electrokinetic potential. Okay. This definition you must keep in mind. Two more points we have to discuss over here. Heading right down. Coagulation. On this, you will get the question. Okay. What is coagulation? No, how do we prevent coagulation? What is the method for that? This is important. So whatever we are discussing now in the half in the last half an hour or 15, 20 minutes on this portion in J. They ask questions. Okay. This is what you need to understand properly. There are a few things. Obviously you need to memorize coagulation. We also call it as precipitation. Precipitation. Or it is also known as flocculation, flocculation. All three terms are same. Definition. First of all, you write down. So isn't flocculation just a special case when it floats out in the top? When it floats up to the top. No, it's not float. It's nothing to do with the floating. Flocculation is. Then so there is a term then right for that that starts with F. That is a different. That is the floating nature, right? You're talking about when the floating is different. It is flocculation. Flocculation is aggregation of particles and settling. The flocculation is aggregation, which results into settling. And then in turn it loses the quality. Okay. So flocculation is different. Loading is different, which there is at the surface. Okay. So right on precipitation, you understand. No. That is a formation of precipitate. Same thing. You can understand coagulation and flocculation. Same time we have. So right on the definition here, the process of settling. Of colloidal particles. The process of settling of colloidal particles is called. Is called coagulation. Or precipitation or flocculation. Okay. So simply what happens when the particles aggregates. Right. Combines. Then it settles because of its mass. That we call it as coagulation. In coagulation, what happens? The particles or solution or mixture loses its colloidal property. Correct. Next point right on coagulation of lyophilic soil. Coagulation of lyophilic soil is very difficult. Coagulation of lyophilic soil is very difficult. Coagulation of lyophilic soil is very difficult. Since it is attracted towards water molecule. Since it is attracted towards water molecule. Which forms a layer around it. Around its particle right now. Which forms a layer around it. Around it means around the particles of the collides. And hence the coagulation becomes difficult. All these yellow circle that I have done. This is water molecule you assume. Water molecule. I'm talking about lyophilic now. Lyophilic. Okay. See coagulation you try to understand this way. Assume like we have a colloidal solution. We have a colloidal solution. So in the colloidal solution, we have obviously some charge. Correct. So I'm suppose that we have a positive charged colloid. So we have everywhere we have positive charge present. And then we have repulsion, which does not let the particles settles down. And hence the colloidal solution is taken. By any means, if you are able to neutralize the charge, then coagulation is possible. No. Yes. See, we all know that collides are stable because of repulsion. If you remove the repulsion by any means. It won't be stable. And then it settles down right precipitates. Correct. So how can we achieve this coagulation by neutralizing charge on it? Isn't it? Right. Right. Yes, guys. Tell me. Yes. So how do we do it? One way is what we add excess of electrolyte here. Excess of electrolyte. So if you're adding excess of electrolyte, that is what I was talking about that. We must have a requested amount of electrolyte present in this. If you have excess of this, then the negative part of the electrolyte will neutralize this and then coagulation takes place. Right. So one way is what excess of electrolyte you add. Another way you boil it. Another way electrophoresis. Another way is what by persistence dialysis. So there are many different ways. I'll tell you two, three points we have. I'll tell you what it is. So we were talking about first, lyophilic salt. So lyophilic salt, what happens? The point we all come to this conclusion now, that till we have the charge present, it is stable. You neutralize the charge, it becomes unstable, coagulation takes place. So in lyophilic salt, what happens? Suppose it is a positive charged soul. Water molecule is attracted towards it. So water molecules forms a layer on its surface. So because of this layer, the negative charge electrolyte, if you have any, which you are adding here in order to neutralize the charge, this CL- is not powerful enough to penetrate the layer created by water molecule, goes into the bulk of it and neutralize a positive charge. So it could not, it, actually it cannot, you know, penetrate the layered forms by the water molecule. Hence it is not able to neutralize a positive charge, which makes the soul stable, lyophilic soul stable. So this is a reason for the stability of lyophilic soul. It is water loving, forms a layer, which is not penetrated by any oppositely charged ion. Hence we say that lyophilic soul is quite stable. But this does not go, you know, go with lyophobic salt, because it is water repellent, right? It, water does not form a layer. You add an electrolyte over here, NF, excess of electrolyte, it will neutralize the positive charge and coagulation takes place, right? So how do we prevent the coagulation of lyophobic soul? Right, that is also one case we have. First of all, you see, the right or next point, the coagulation of lyophobic soul can be carried out by, can be carried out by boiling, just point-wise right now, nothing, you don't have to write down the entire theory over here. Can be carried out by boiling. Second one, by mixing two oppositely charged soul, oppositely charged soul, third one by electrophoresis, electro, P-H-O-R-E-S-I-S, electrophoresis. Electrophoresis is similar to electrolysis, in which we have electrolyte, we allow this to pass through that device in which the electrophoresis is taking place. So all the positive charge particles moves towards the opposite charge electrode and there it gets, you know, reacts with the water like oxidation reduction and it gets discharged over there. So electrophoresis is that. So these three, where we have, by which we can achieve coagulation of lyophobic soul. Lyophilic, it is difficult. I have explained you the thing, okay? Yeah, tell me. So what is the spelling for the last word, electrophoresis? Electrophoresis, electrophoresis is this, electrophoresis, electrophoresis, electrophoresis. And say, I think we have to read this. Basic concepts is similar to electrolysis. Ions, whatever ions we have, if it is positive charge, move towards the negative electrode and it will get discharged over there. So our objective is to neutralize the charge so that we can achieve or we can get coagulation, right? So electrophoresis is similar to that. One, the important one, the fourth point to write on, on which in J they have asked question, what is that question that also we'll see, kind of question, write down by addition of electrolyte, by addition of electrolyte. In this, you write down, when an excess of electrolyte is added, when an excess of electrolyte is added. Wait a second, is this under coagulation? Sorry? Is this under coagulation? That is what we are discussing. We are discussing, what are the ways by which coagulation possible? Oh, okay. Right, so three points I have given you. I've given you by mixing two oppositely charged ions, souls, electrophoresis, boilings, right? Fourth point is by addition of electrolytes. Yes, guys? Yes. Fourth point right now, when excess of electrolyte is added, the colloidal particles precipitates due to neutralization, due to neutralization. Next slide. The ion which is responsible for coagulation is called coagulating ion, or no, flocculating ion, anything you can say. The ion which is responsible for coagulation is called coagulating ion or flocculating ion. If you have a positive charged soul, what could be the coagulating ion? Negative or positive? Negative. Negative, opposite. If you have a negative charged soul, positive ions are the coagulating ion, common sense. Now, which, you know, we have in this, we have a certain rule, right? Which depends upon the coagulation capacity of electrolyte right? This rule, we call it as hardy suzerule. Okay, the name is weird, but yes, this is the name. Hardy, very simple, easy. S-C-H-U-L-Z, hardy suzerule. Okay, write down, write down the coagulation capacity is different for different ions, different electrolytes, sorry, coagulation property is different form for different electrolyte and it depends upon the valency of the active ions. Active ions means you can say coagulating ion, same thing. And it depends upon the valency of the active ions. Repeat it once. Yeah, I said it depends upon, from the first line you said, first one you have written? No sir, I missed that. In the beginning you can write down the coagulation capacity is different for different electrolytes, is different for different electrolytes and it depends upon the valency of the active ions or better you write coagulating ion. Next slide, continue. According to this rule, greater the valency of active ions, greater the valency of coagulating ion, greater will be its coagulating power. So this rule says what, that the coagulating power, coagulating power is directly proportional to fourth power, fourth power of the valency of fourth power of the valency of active ions. Relation is not important. You just need to know more valency, more will be the coagulating power. So what kind of question they ask? They will ask you questions like this. We have a soul of AS2, S3 for example. They can ask you the coagulation is possible with what electrolyte? They'll give you four options, A, B, C, the ions they will give you here. Or which one will give the maximum coagulation for this electrolyte? For example, we have ALCl3 present, AL3 plus we have, Mg2 plus we have, Na plus we have. And one more, what we can write. NaCl, which one will give maximum coagulation? AS3 plus. Obviously, so for this, what information you should know? If you know the charge of this soul, correct? That is the only thing you should know. If you know this, you can do this. That's why I said charge you have to memorize. And on this only JK point of view, this particular thing is very important. So questions B, you will solve the question, you will get the questions on this. Only one information you need, the charge on the soul. That's why whenever I have given you four or five examples, when you solve the questions, if you see some different soul is there, charge is mentioned, just write down in your notes. If you know the charge, four marks will never go anywhere. So very important, easy questions you will get. So we know the charge on sulphide is what is negative charge soul it is. So negative charge soul will get, you know, coagulated by the positive charge electrolytes, right? So positive electrolytes is more, positive charges more, more will be the coagulation. Obviously it is AL3 plus, right? So this kind of questions you get, right? So this is the coagulation of collides. And then what are the, you know, how do we know that coagulation takes place for which electrolyte, what ion should be there and which one will give the maximum coagulation. Now, how do we protect the collides from coagulation? Right? How do we protect the collides? So protection of collides, right? Next heading, the last point we have in this, protection of collides from coagulation. One way is what? The addition of lyophobic soul I'm talking about, okay? Protection of collide because lyophilic soul is already stable. So we are talking about lyophobic. So if you want to stabilize lyophobic soul against the coagulation, you can add lyophilic soul into this, add lyophilic soul. What it does, this lyophilic soul, it surrounds the particle of lyophobic soul, right? It surrounds the particle of lyophobic soul, which, you know, which, which does not let the opposite charge ion on any electrolyte attack onto the lyophobic particles. Correct? So one way is what? One way we can add lyophilic soul into lyophobic soul. Write down, add lyophilic soul. This is only write down. Lyophilic soul are extensively solvated. Lyophilic soul are extensively solvated, which does not let, which does not let the electrolyte to attack onto the lyophobic particles. Sir, could you repeat that? I said what, that this is due to the fact that lyophilic collides are extensively solvated, extensively solvated. It does not let the electrolyte and it does not let the electrolyte to attack on, to attack on the lyophobic particles. And that is why lyophilic soul, we also call it as protective soul. Lyophilic soul protects lyophobic soul. What I have written, lyophobic. This is not done. Lyophobic soul, now I have written state. One second. Lyophobic soul, yes. That's why lyophilic soul, we also call it as protective soul, the other name of this. It protects the lyophobic soul from coagulation. Now, if you need to find out the capacity of a protective soul, that is lyophilic soul, how capable it is. If you want to understand the capability of lyophilic soul, that to what extent or how, to what extent it can protect the lyophobic soul from coagulation. We have a number for that. We have a term for that basically, yes. And that term, we call it as gold number. So gold number actually defines the capacity of lyophobic soul, that is protective soul, that how it can, to what extent it can protect the lyophobic soul from coagulation. So heading right down, so in this only, you write down the next term, gold number, definition right down. So it basically, express the strength of lyophilic soul, that is a protective soul. It is the number of milligrams, I'll write it down. It is the number of milligrams of protective colloid, protective colloid that will prevent, that will prevent the coagulation of, coagulation of 10 ml, 10 ml of a gold salt, of a gold salt on addition of, on addition of 1 ml of 10% NaCl solution. So if you have 10 ml of a gold salt, right, and you are adding 1 ml of 10% NaCl solution. Gold salt is positive or negative? Negative. Negative, right, you are adding NaCl. So Na plus will, will try to flocculate the soul, right. 10% NaCl you are adding, 10 ml of gold salt we have. Then the amount of protective salt is required to prevent the coagulation of this. That we call it as the gold number for that particular soul, right. Done. So suppose we have one protective colloid, one protective colloid and its gold number is randomly I am assuming it is 10. It says the number of milligram, means 10 milligram we have gold number, right. Gold number is 10, I should write down 10 only because it only says number of milligram. So it automatically means 10 milligram. Protective colloid one we have and we have protective colloid two. Its gold number is suppose 15. Tell me which one is a better, better protective colloid. One. One because it requires one is better because the gold number is less. Lesser amount can prevent the coagulation of the 10 ml of gold salt, right. So power if you see capacity if you see capacity or power of colloid one is more. So what we can conclude gold number is inversely proportional to protective, the power of protective colloid. Can we say that? So some compounds and its gold number and just write down here. So do we need to remember these numbers? Sorry. I have seen a couple of questions on which they have asked this question like which one is a good or better or the best protective colloid for this particular soul, right. It is given. So sometimes what happens, you can identify this with the charge if AL3 plus MG2 plus NA plus we have so obviously if the colloid is negatively charged you can say AL3 plus is the best one. But yes, when the question is all about when the charge is same then you have to go by gold number, right. So that AL3 plus will, what it does it will coagulate. NA plus will coagulate the least among the three. So NA plus we can go for that if the question is like that. But if the question is directly also one question I have seen they have asked which one has the maximum gold number like this or which one has the maximum protective path these kind of questions you have to do by gold number. So you don't have to memorize it I don't see it as that important because only couple of time I have seen this kind of question they have asked. So it is not important, but yes one or two example you should keep in mind that this one is the best one this one is the least one like that. I'll give you some examples you can gelatin you see the gold number is 0.005 to 0.01 if you talk about hemoglobin the gold number for hemoglobin is 0.03 so which one is better in this too. That gold number is least of a gum Arabic gum Arabic 0.15 not important at all. Egg albumin this kind of question they ask in CET kind of example. Okay so once you prepare for CET so this chapter and then polymers biomolecules also like the protein related questions those kind of portions you must revise. Egg albumin its gold number is from 0.08 to 0.10 Potato starch 0.25 okay starch only 0.25 to 0.50 so basically in general you can just keep this in mind that gelatin is a very good you know productive colite starch is not a good product. But yes when you prepare for exams like CET and all this kind of these portions are important they ask questions directly from this. So we are done with this chapter this is what we need to do. Apart from this we have some more things like gels emulsions like those definitions you can go through emulsions you already know milk is an example of emulsions right. So I'm not giving you those things and everything we have covered in this we have done in so detail. Just go through the questions once okay you will have the idea of the important portions in this chapter. You don't have to revise this chapter on any basis but yes before the exam like I said you will have the RDSSUSA rule right charge of the colite okay and absorption absorption graph comparison graph that you had those things plus this one the last half an hour that we discussed these things are important for GE so you can revise these things before the exam correct. So we'll start next the practical organic chemistry qualitative quantitative analysis that is salt analysis correct salt analysis the radicals you know just a second


I've been in for 20 years, obviously the Marine Corps has afforded me many opportunities and I didn't realize that this was something that was available to us. Being able to participate in this course while I'm on active duty, being able to spend the last six months of my career transitioning into another field. For the past 18 weeks, I've received an incredible amount of guidance that allowed me to go in there and just rocket. My resume would have never gone through to even get me in the door, so this academy takes us and puts us way ahead of the pack. Out of our course, about 19 students, all of us were able to get a job through this. They're looking for your soft skills and your aptitude to learn and as long as you have those, this program will get you set up for success. Thank you.


Hurray! It's time to learn to edit. You'll make today a movie project and learn how to import media into iMovie. So what you're going to do is you're going to look for the purple star in your doc and double-click it. So we've got three buttons at the top of the screen that opens in iMovie. There's media, there's projects, and there's theater. Let's start with projects. And if you would create new, and when you press on that, it asks you if you'd like to create a movie or a trailer. Click on Movie, and you'll see that it created a movie. It's called My Movie. Here it is up here. They've named it for you. Well, we don't want it to be called My Movie. Let's click on Projects again, and let's call it Injects Drone. Okay? And click OK. So now we can see there is our project, and if you click on it, it brings us to this window. Now you won't have this information here, but you will in a minute, I promise. But if we look at Engineering Drone or Injects Drone in that window, or if we click on the word under Project Media on the far left, Injects Drone, it will ask us to import media. So go ahead and click on that arrow, and up at the top, it's going to ask you where you want to import the footage to. What we want to import to is something called Injects Class. So go ahead and type in Injects Class. It's not having me type it in because I've created it before. So go ahead and list that. And then you are going to look for the media to import. Now there's many ways you can import media, and I'm going to show you all of the four ways for media that's on your computer. So the first thing, the first method to import footage is to go up to your menu bar, which is at the top of the screen, press File, File, Import Media. And this is called the Import Window, and it will ask you to find the footage that you want to import. It happens to be on the desktop, and it's in a folder called Injects Media. So double click on that, and you'll see the same thing that's on my window right now. And what you want to do is come over here and say Import All. So that's one way to import media, and that's going to be in our Injects Class event. And we can see that here, Injects Class. So we have the event, Injects Class, and we have a project, Injects Drone. So that's one way you can import. But there's actually three additional ways. You can press the Import button, which is at the very top of your screen. It's the arrow. If you click on that, there is our Import Window again. So just know you can import by using that. You can also drag and drop, which I just love. And I'm just going to take this. It's already there, but let's see. Drop it. And there it is. And I can say import that. But if you were just to drag and drop, you'd click Import Selected right here. So that's a third way. So what's the fourth way? When you use iMovie for quite a while or any software, there's something called Keyboard Shortcuts. So this is a keyboard shortcut. This little symbol with the letter I. And that stands for Command I. So you can actually go to Command I, and you'll get the Import Window. And then you can import from there. So those are the four ways that you can import footage. And here they all are. Here's all the footage we imported. And we'll be looking at that shortly. The footage files are copied into iMovie and also into what's called the Movie Library. iMovie basically makes a copy of your files when you import anything. And it places them in a separate folder called iMovieLibrary. So in actuality, we don't need to save the engineering X folder on our desktop. We can actually delete that. And video takes up a lot of space.  We do, however, want to back up using a hard drive. And we'll be doing that as well. So I only showed you here how to import footage from files that are already on your computer. But you should know that there are other methods. What if you have footage on a video camera? And maybe it's an older camera that has a tape drive in it or a camera that has a hard drive in it. Or maybe it's a newer camera that uses memory cards. How do you get that in your computer? Well, if that's the case, what you have to do is use the ports on the side of your computer and cords to connect your cameras to your laptop and bring footage into iMovie that way. So you did it. You've seen four ways to import footage. And those four ways are what? Who can tell me what they are? We're going to stop here. We're going to let you play and feel free to ask questions. And we'll talk a little bit with the coaches as well.


Hello, everyone. Welcome to a video lecture on frequency reuse. I am K. R. Biradhar, assistant professor, department of electronics and telecommunication engineering, Vulture Engineering Stop Technology, Saulapur. Let us start with the learning outcomes first. At the end of this video, you will be able to design cellular system with minimum signal to interference ratio. Cellular systems, some of the basic concepts. Before discussing the frequency reuse, let us see some of the basic concepts of cellular system. To begin with, high capacity is achieved by limiting the coverage of each base station to a small geographical area called a cell. Same frequencies or time slots or codes are reused by specially separated base stations. This factor of being reuse allows you high capacity so that large number of customers more revenue from the system. A switching technique called handoff is used here to enable the call to proceed uninterrupted when one user moves from one cell to another. Neighboring base stations are assigned different group of channels so as to minimize the interference. What do you mean by channels? We have seen earlier certain frequencies or time slots or codes and they form the channel. Therefore, neighboring cells must not use same frequencies but we have to use it after some definite distance so as to minimize interference. By systematically spacing base stations, the available channels are reused as many times as necessary. As demand increases, the number of base stations may be increased thereby providing additional capacity. So, there are ways and means today to expand your services. If your number of customer increases, you can scale up your system. So, this reuse factor and certain other advanced techniques will allow to continue providing services to a more and more number of stations. Even though you are not asking for extra bandwidth, cellular system design fundamentals to solve problems of spectral congestion and user capacity, replacing a single high power transmitter with many low power transmitters. Neighboring base stations are assigned different groups of channels so that the interference between base stations is minimized. Fixed number of channels to support a large number of subscribers. High network capacity is achieved by keeping same cell reuse distance high so that the interference caused is kept sufficiently low. Frequency reuse, the procedure of allocating the channels is called frequency reuse. In other words, the design procedure of allocating channel groups for all of the cellular base station within a system is called frequency reuse or frequency planning. Large distance to keep co-channel interference within limit. By design of antennas, the same area is limited within the cell and the same group of frequencies is reused to cover another cell separated by a large enough distance to keep co-channel interference within the limits. Why a large enough distance because you want to keep a co-channel interference which is generated by cells using the same frequency under control. Intelligent allocation and reuse of channels, cellular radio systems rely on intelligent allocation and reuse of channels throughout the coverage area. Each base station is allocated a group of radio channels to be used within the small geographical area of its cell. Concept of frequency reuse, the figure shows the concept of frequency reuse. There are seven cells which are represented by different letters A, B, C, D, E, F and G forms the one cluster. These are also called adjacent cells use different frequency band to avoid interference. This cluster is replicated all over the geographical area. In the diagram, same cluster replicated after some distance forms cluster 2. Note that the cell A present in the first cluster is repeated in cluster 2 with same letter as cell A. The distance between these two cells is called reuse distance. It is interesting to know you cannot have any random number of cells in a cluster. You cannot have a cluster size of 5 cells. One more thing is if the cluster size is small say for example 4, reuse distance will go down, capacity will increase but at the same time interference increases. Capacity of cellular system here S denotes number of duplex channels available for use or total number of duplex channels. Small key represents number of channels assigned for a cell. Capital N represents number of cells sharing S channels that is also called the cluster size. Therefore, S is equal to small k into n. C represents total number of duplex channels with frequency reuse. M is a number of replica of cluster. Therefore, C is equal to m into k into n. k in already you know that is equal to S. Therefore, C is equal to m S. Let us see one example. Given total available bandwidth is 30 megahertz, channel bandwidth is 50 kilohertz for duplex channels. Each cell has how many channels for 7 cell reuse? First the video and write your solution. First the video and write your solution. First the video and write your solution. I think you might have written the solution. Let us see here. The total available channels for given spectrum is 30 megahertz divided by 50 kilohertz is equal to 600 channels are available. k is equal to 600 divided by 7 that is 85 channels are available in each cell for n is equal to 7. Here k is the number of channels in each cell and n is the cluster size. Identify number of cells in a cluster. In order to identify the number of cells in a cluster we use the formula capital n is equal to i square plus i j plus j square. Take for example, i equal to n j equal to 1. Therefore, n is equal to 2 square plus 2 into 1 plus 1 square this is equal to 7 cells. In a cluster as shown in the diagram identifying the core channel cells. In order to identify core channel neighboring cells consider this figure having n is equal to 19 cells reuse and having i is equal to 3 and j equal to 2. Move i cells along any chain of hexagons in this example it is 3 turn 60 degrees counter clockwise and move j cells that is 2 in this diagram. In this way you can identify the core channel cells. These are the reference I referred to prepare the above presentation. Thank you. Thank you.