 Hello, good afternoon, everyone. Hello, everyone. Can we start now? Yes, sir. Okay. So guys, today we are going to start surface chemistry. Okay, and we'll finish this chapter today itself. And tomorrow or the day after we have, we'll have one more class. So there then we'll start P block in the next class. Okay, whenever we have First of all, let me Can you see now? Yeah. So Surface chemistry is the last chapter of physical chemistry we have. Okay, we are left with chemical kinetics In this physical chemistry portion. So that will do in offline class chemical kinetics. Okay. Organic we have almost done our minds. We have finished biomolecules. We have done Right. So there are a few chapters left in In organic chemistry that we'll focus on. So surface chemistry in this chapter. First of all, there are two, three things after is not that big. First of all, two, three things are very important here. And that is In J they have, they ask questions on this chapter. Okay, it's not like the chapter is small and not that conceptually vast. They won't ask, they ask questions from this chapter in J exam. The book you have to go through for this particular chapter is NCRT. They ask questions from NCRT itself. Okay, so you have to thoroughly read NCRT for this chapter. Okay, all those concepts which are there that we'll discuss, but NCRT you must go through. Okay. Okay, so let's start with the chapter we have the surface chemistry is what it is this actually this chapter deals with the Phenomenon that occurs at the surface or interface. Okay. So what we are going to study in this chapter that it deals with deals with the phenomenon, the phenomenon or chemical process phenomenon or chemical process that occurs at the surface, the process that occurs at surface or or we can also say or the interface or the interface of two phases. When two phase interacts, so that interface what chemical process is there, what phenomenon is there, what is actually going on that we discuss in this chapter. Okay, one type of process we have already familiar with, and that is absorption, absorption, absorption, we know this term properly. Okay, what is absorption and all the another term here, we are going to introduce in this chapter you must have heard about it, and that is adsorption. The basic difference of absorption and adsorption, you know already that adsorption is a surface phenomena phenomenon and absorption is a bug phenomenon. Okay. So what happens adsorption if I try to make you understand this particular process. The best example is suppose you if you take a chalk. Okay, suppose you have a chalk piece that we used to write on blackboard and all is the chalk piece and a foam foam sponge that we did. Now when we dip these two into a vessel, which has ink into it. This is suppose we have blue, black, whatever color ink we have into this, when we dip this chalk piece into this ink, then what happens around the, at the surface of this chalk, there is ink present. And this, this ink won't go into the bulk of this chalk. Okay, if you dip this for a few seconds. Okay. But this sponge of foam, it is completely dipped with or the ink molecule or particles is uniformly distributed in the entire form or response that you have, it is completely occupied with the ink. Okay, so this is two different process we have here the distribution of ink particle is uniform that we assume. And here the distribution of ink particle is only at the surface at the outer surface of the chalk piece that you have. Okay, so basically in technical term, if I say, in this particular process what happens, there is a difference between the concentration at the surface concentration of what concentration of ink difference between the concentration at the surface and the work of the chalk piece. Okay, concentration is different at surface we have more concentration, and in the bulk of this chalk piece, we have less concentration, or minimum or very small, the concentration is very low over here in the bulk of this liquid. So this kind of process is nothing but adsorption, where the particles get accumulated at only the outer surface of the molecule. Got it. And this is what, where the particles are there at the outer surface, as well as the inner surface that we call it as sorption. Okay, you let it be. Okay, this I'll just come to this a few minutes later. Did you understand what is adsorption? adsorption is what adsorption is the definition of adsorption you write down. It is the tendency of adsorption. It is the tendency of accumulation of, of molecular species, accumulation of molecular species at the surface, at the surface, right, this is adsorption. It is what since the accumulation of molecules takes place at the surface. So adsorption is a surface phenomenon, surface phenomenon. Okay. Now you see there are two types of molecule we have. If I talk about this surface here, suppose we have a surface like this, a molecular surface we have like this. Okay. In case of adsorption, what happens, the molecule which adsorb at the surface, here we have adsorption, right, these are the molecules which accumulates at the surface of outer surface of this particular molecule. This is adsorption. There are two types of molecules we have, the one which adsorb at the surface. And the other type of molecule is what the surface at which adsorption takes place. Okay, so to define these two molecule, the one which get adsorbed and the adsorption takes place on the surface. Okay, so two different molecule we have the molecule where adsorption takes place. On the surface where adsorption takes place is called adsorbent. Okay, so we define these two, you know, molecules by a term called adsorbent adsorbent. And the another term we use here is adsorbate adsorbate. Okay, adsorbent right down the definition of it, the material or the molecule, the material or the molecule at which the material or the molecule at which adsorption takes place. So, in short, if I write down the surface at which the surface at which adsorption adsorption takes place, the surface at which adsorption takes place are called adsorbent is called adsorbent. And the molecule which accumulates at the surface of adsorbent called adsorbent. Okay, so adsorbent are the molecules. So adsorbent are the molecules which accumulates, which accumulates at the surface of adsorbent surface of adsorbent. Copy down this. Done. You know, one second please. The engine cave is done. Sir, finished morning itself. How was it? Very bad for me. How about you, Gaurav? I don't know, sir, I think I did okay. Okay, copy down first. Okay, can we move on? Yes, wait. Kavya, Andrew, Sana, wait for a minute. Yes, sir, thank you, sir. Done. Okay. This three diagram you see, suppose this is a adsorbent we have adsorbent. Another adsorbent is suppose this and adsorbent is this suppose we have three different arrangement I'm taking here. This molecules are the molecules of adsorbent. Okay, the blue one is that adsorbent where the adsorption takes place. And this orange one is adsorbent adsorbent. So this is the two possibility we have. And last one is this where we mix the two possibility means the adsorbent molecule present at both surface and the bulk of this molecule. Okay, this this process where the adsorbent I'll write down here. This is adsorbent and the blue one is adsorbent. So if you see the difference in these three, the first diagram, it says that the adsorbent molecule present only at the surface. Second one, the adsorbent molecule present only on the bulk. It is not at all present at the surface and third to both kind of arrangement we have surface as well as the bulk of the adsorbent molecule. So this process the first one is actually adsorption. This one is adsorption where the molecule present only at bulk. This one is adsorption adsorption. And the last one is sorption. So practically the things that happens is sorption only sorption takes place. These two are the ideal condition we are assuming right. It is not possible that when you dip a molecule into the dip and adsorb and adsorbent into an adsorbent. Then the chances are very less that the adsorbent molecule are present only at the surface or only at the bulk, but this probability is very high. Actually, this happens. This is the two ideal condition we are assuming that when the adsorbent molecule at the outer surface, it is adsorption only in a surface absorption and both is there than sorption. Okay, so this actually happens practically this two are we are assuming. Okay, this is one thing. This process adsorption it is an instantaneous process instantaneous process occurs very fast very fast process. Okay, adsorption is a like I said it is a bulk phenomena bulk phenomenon. And comparatively slow in nature. Okay, sorption is a mixture of both adsorption plus absorption adsorption plus absorption. Okay, like example is what die on cotton fabric on fabric simply right on fabric. That is an example of sorption. Okay, for adsorption one technical thing also you have to keep in mind that we must because like I said we are assuming adsorption like in the first diagram I haven't drawn any adsorbent molecule present in the bulk of this molecule. Correct, but actually there are few molecules present here also in adsorbent. So what we define here that the concentration at the surface and in the bulk of this molecule there must be some difference into that. Okay, so concentration at the surface is high in comparison to the concentration of the bulk of the liquid. Okay, so for adsorption what we say there must be a difference in concentration difference in concentration of adsorbent adsorbent between the surface and the bulk of the molecule and the bulk simply right on this one. Another thing here you see write down the adsorption of gases on metal. This question they have asked an exam the adsorption of gases on metal on metal surface is called is called occlusion is called occlusion. Okay, for example H2 when present in the pore of palladium pallet platinum. This is an example of occlusion and the hydrogen which is present in this we call it as occluded hydrogen. So definition based question they have asked on this what is occluded hydrogen like this they have asked question. Okay, so H2 which is present here we call it as occluded hydrogen. This is one thing. Can I go to the next page? So just a second. Now the next we have to understand what is the mechanism of adsorption. So heading all of you write down mechanism of adsorption. See there are for driving force for this process adsorption is the two things we have to consider. One is one factor is residual force residual or unbalanced force. And the second one is thermodynamic factor. See I'm not dictating here anything to you. So whatever I'm writing it down just to copy this okay in your notebook properly and if you feel like because I'll say everything. So if you feel like this point is important you copy it down just write it down residual or unbalanced force. Okay, see what happens here. Suppose I'll take a water molecule. Okay, so assume this is the water molecule we have. This is the surface. This is the water molecule we have. Assume two molecules. I'm assuming two molecules here one molecule which is suppose this side we have all these are adsorbate molecule. Right if this molecule comes closer to this adsorbent surface is adsorbent. This is water adsorbate and adsorbate molecule. So when it comes closer to this. So you assume here suppose this molecule it is true for all the molecules here. If this molecule present here at the surface of it water which is the adsorbent. Okay, so the atoms which are close to this particular molecule they will have an attraction they will exert an attraction force on this molecule. So we'll have a force in this direction will have a force in this direction this direction this direction means the net force will be in downward direction. Okay, but you assume a molecule here which is in the bulk of this liquid and around this will have water molecule present or any other molecule it is completely surrounded like this. Okay, so all kind of force if you consider here which is acting in this direction this force is getting balanced by this this force is getting balanced by this this force is getting balanced by this. So here what happens in this bulk of this liquid if any molecule is present in the bulk of this liquid. There is no net force no net force net force is equals to zero that's why it is you know balanced but here what happens here. We have net force in downward direction in downward direction. So all those adsorbent molecule which is close to the surface of this adsorbent will experience a net force in this downward direction. Right, so because of this unbalanced net force which is nothing but the residual force unbalanced force unbalanced force the adsorbent molecule is attracted towards the adsorbent molecule. Obviously this force is not that sufficient then this will overcome the force of buoyancy here and hence the molecule won't go into the bulk of the liquid. So that condition we are not assuming adsorbent adsorption is only possible when this force is sufficient enough to keep this adsorbent molecule at the surface of the liquid. If it is high enough this molecule will go into the bulk of this liquid that condition I'm not taking we are not taking. So for adsorption the condition is satisfied here what that the net albinus force is just sufficient enough to keep this molecule on the surface of this liquid. Is it clear now. Right, so now you see what happens if you talk about in terms of bond here. So initially there were no bond present between this molecule and the adsorbent molecule. Now when this because this attraction force there is a kind of bond present between these two molecules and all these molecules adsorbent molecules are attracted towards the adsorbent. Correct and bond formation is what bond formation is in exothermic process. Right, so because of this attachment this bond some energy goes out in the form of heat. Okay, and that is why this process we call it as exothermic process. Am I clear with this. Yes. Delta H less than zero. Okay. So this is actually first of all this residual unbalanced force because of that only the molecule is attached to this adsorbent adsorbent molecule. And in this process some energy goes out in the form of heat. And that is why the process is how do you memorize this you can assume this as a bond formation and bond formation is always an exothermic process. Okay, now if I talk about entropy of the system when this attachment takes place entropy decreases or increases. Increases, right. Wait, no, no, no. Lesser than zero or greater than zero. I get it. What? See that now when the bonding takes place because of this unbalanced force of attraction. Then the adsorbent molecule is not free to move. to move. Its motion is now seized, hindered, right? So entropy should be what? Delta should be less than zero, right? So right down this point here, when a gaseous molecule, gas is adsorbed, when the gas is adsorbed at the surface, adsorbed, let it be, the movement of, the movement of gaseous particle, gaseous particle seized and hence randomness decreases, means entropy decreases. So delta S for this process is less than zero. So for two process what we can write that delta H is less than zero for adsorption, delta S is also less than zero. So if I write down Gibbs Helmholtz equation, that's delta G is equals to delta H minus T delta S. So for the process to be spontaneous, what is the condition we should have? Low temperature or what we can say the magnitude of delta H means the energy increases here should be more than the magnitude of T delta S. And for this, we need to decrease the temperature, okay? And we also say this theoretical question they ask. We also say that the adsorption is taking place by decreasing enthalpy as well as the decrease in entropy, write it down. The adsorption is taking place by decrease in enthalpy and the adsorption is taking place by decrease in enthalpy as well as the decrease in entropy, decrease in entropy, okay? So adsorption, mechanism we have discussed. Now there are two types of adsorption we have. Adorption there are two types. The first one is physisorption or we also call it as physical adsorption, physisorption or physical adsorption. And the second one we have is chemical adsorption, chemisorption or chemical adsorption, okay? The basic difference between these two adsorption process is in physical adsorption what happens, write down the adsorbent molecules, the adsorbent molecule attached with, attached with the adsorbent molecule with weak van der Waals forces. Sir, could you repeat it again? adsorbent molecule attached with the adsorbent molecule with weak van der Waals forces. There's a weak van der Waals force. And that's why we also call it as van der Waals adsorption, okay? So this kind of adsorption is possible because of weak van der Waals forces. And hence, we also call it as van der Waals adsorption, okay? There are two, three properties for this adsorption we have. Like first of all, here we have weak van der Waals forces. In case of chemical adsorption or chemical adsorption, the reason of, you know, the attraction between adsorbent and adsorbent is, is chemical bond, okay? Means the adsorbent and adsorbent molecule are attached together by chemical bond. So here we have chemical bond between adsorbent and adsorbent molecule. And here we have van der Waals forces, okay? Now you can easily compare these two. Like we have weak van der Waals forces. So we can easily overcome this force. One thing I forgot to tell you here, you see this diagram, this process, when you have this adsorbent molecule present onto the surface is adsorption. So if you remove this adsorbent molecule from the surface, it is the reverse process of adsorption. And we call it as desorption, okay? Reverse of adsorption is desorption, okay? Yeah. Hello. Are you there? Yes, we're there. So reverse of adsorption is desorption, okay? But this desorption process is not possible when chemisorption is there because chemical bond is comparatively stronger. It is very difficult to reverse the process, okay? So the second difference here is, first of all, the nature of, you know, bond is different. Here we have weak van der Waals force. Here we have chemical bond. The second difference is what? That this is a reversible process, okay? Since we have weak van der Waals force, okay? So we can easily overcome this force by increasing temperature a bit, okay? So we can easily overcome either by increasing temperature or by decreasing pressure. That's why it is reversible in nature, right? Down either by increasing temperature or by decreasing pressure. So this is weak van der Waals force. We can overcome it and hence it is reversible in nature. And this one is irreversible, irreversible. And since there's a chemical bond, so this forms unilayer. This forms multilayer, okay? Unilayer, multilayer. Can you tell me, we have already discussed that there is some heat evolve in this process, adsorption, yes? Can you tell me in which of these two processes the heat evolve is more? The amount of heat that comes out in this process, right? I think chemical adsorption. Biochemical adsorption? Bond is formed, so it's a strong bond, so more energy is released. Krishna? So strong bond, so more energy is released. I got Krishna there, no? Yes sir. Good, okay? Chemical bond is stronger, right? So more strong bond forms, it means, it means what? More energy comes out. So what we can say, the heat of adsorption here, it is more, more heat of adsorption and here we have less heat of adsorption. See white forms multilayer, you see this diagram here. Suppose we have adsorbent molecule like this. This is the adsorbent molecule we have, okay? This adsorbent molecule will have adsorbent present on its surface like this, okay? Since this is a weak Vendaval forces because of, and this happens because of charge separation. So when this attached to this, this will have some charge on it and this will also attract the another adsorbent particle, which is there present in the other layer, the next layer you can see. This will also exert with this and that's why it forms multilayer like this, okay? Because it is a Vendaval force, so the force of attraction depends on distance. For a certain distance, the force of attraction will be there and hence it forms multilayer structure. Here what happens, there's a chemical bond between the adsorbent and adsorbent molecule and once the chemical bond already formed, it forms a layer further with another layer, the bond formation is not possible because one bond is already formed. There's a bond between these two, chemical bond. So the another layer won't form into this because the chemical bond is already formed. It is not attraction force so that the other molecule also get attracted towards it. That's why we have here unilayer and this side we have multilayer. Got it? If I give you the value here, which is not, you know, that important to memorize, but in this case, we get 20 to 40 kilojoule per mole of energy releases into this and in this case, it is somewhere around 82 to 40 kilojoule per mole of energy releases. Okay. The easy option is not specific in nature. The another difference you write down, it is non-specific, non-specific in nature, but this one is a specific because it forms a chemical bond, right? So we know between two atoms, like chemical for chemical bond will have a certain condition to be satisfied. That's why chemical bond does not form between all kind of molecules, okay, among all kind of molecules. But since this is option is a force of attraction that only requires charge separation, right? That can also be possible with induced charge. Charge induction is also possible. That's why it is non-specific. It does not depend upon what kind of molecule we have. You just need charge separation, correct? So this one we call it as non-specific and this one is specific. One thing also you must take care of in physics option, the amount of gas that absorbed is directly proportional to the ease of liquefaction of that gas, okay? Here write down the amount of gas absorbed is directly proportional to the ease of liquefaction of that gas. Why I'm giving you this and there is no such relation we have here. Here we cannot say liquefaction and amount of gas that absorbed, the relation between that is not true here. But in this case amount of gas absorbed is directly proportional to the ease of liquefaction of that gas. It means what if I ask you there is NH3 and O2, two gases we have under similar condition. So which gas will absorb more? What is your answer? The one which is easily liquefied, correct? NH3, right? Yeah, NH3. Yeah, the one which is easily liquefied and liquefaction tendency how do we observe? Judged by the force of attraction. Force of attraction and that is determined by the Van der Waal constant, correct? And what is that Van der Waal constant? A. So A value is more for polar molecule that we know already. Gas's statement we have done it, revise it once. Okay, so with A value actually you can say that under the given set of conditions which gas will absorb more? Till now they haven't asked this kind of questions. But since they haven't asked they may be they may they may ask this question. Okay, so keep that in mind. The gas which has more A value has more adsorption tendency, physical adsorption tendency. Got it? So here the adsorption under similar condition of NH3 will be more than to that of O2. Got it? Yes. Yes, sir. Another thing which is very important here like I said it is reversible in nature and with increasing temperature we can this can go in backward direction. Okay, so can we say that that as temperature increases adsorption decreases for physical adsorption? Can we say that? So could you repeat? As temperature increases adsorption decreases physical adsorption. That's why I have written here reversible in nature and this nature we can achieve by increasing temperature or decreasing pressure. Okay, so graph of these two I will draw in the next slide. Can I go to the next slide? Yes, sir. Okay, okay, so physical adsorption the graph is this chemical adsorption the graph is this graph is x by m and this is temperature. This is also x by m and this is temperature x by m is what x is the amount of gas adsorbed. Okay, amount of gas adsorbed per unit mass x by m is the amount of gas adsorbed adsorbed per unit mass. The graph that we get here for physical adsorption it goes like this physical adsorption it goes like this at constant pressure as temperature increases as temperature increases the adsorption decreases the pressure is constant here for physical adsorption the graph is this first increases maximum value and then decreases. So the first graph is for physical option right this one is left side is physical light side is chemical okay here also the pressure is constant and constant pressure graph we have this graph we call it as adsorption isobar the both graphs we call it as adsorption isobar okay chemical adsorption what happens as temperature increases okay processes exothermic temperature increases so the amount of gas that adsorbed increases goes to a maximum value and then it is started decreasing because every bond you know it is it gets strong with the value of temperature to some extent if you increase the temperature then the bond becomes weak it can dissociate easily and hence the adsorption decreases the chemical adsorption this graph is experimental but with this graph we can conclude what that first the amount of gas that adsorbed increases goes to a maximum value then the bond becomes weak and adsorption decreases and hence the graph is like this okay so what we can say in chemical adsorption the magnitude of adsorption initially increases and then decreases the magnitude of adsorption increases initially initially goes to a maximum value and then decreases chemical adsorption is this here since we have vendor wall force so with increasing temperature that reaction becomes weak hence it decreases continuously okay can we move on next this actually the same thing we have for the factor affecting the rate of adsorption or adsorption the next topic we are going to discuss here is factor affecting adsorption factors affecting adsorption so the first factor temperature we have already discussed so I am not discussing it again okay temperature temperature we have discussed already okay next write down the surface area the surface area of adsorbent the surface area of adsorbent as the surface area increases as the surface area increases the magnitude of adsorption increases okay more surface area more adsorption okay and all these we are talking about physical adsorption must you take care of that this is physical adsorption right nature of nature of adsorbent you write down nature of adsorbent we have also discussed this that the gas which has more value of a the gases which are easily liquefiable write down like this the gases which are easily liquefiable get adsorbed easily more you know liquefaction convincing more will be the adsorption for the gases nature of gases this pressure you write down at constant temperature at constant temperature the magnitude of at constant temperature the magnitude of adsorption increases initially and then becomes constant at constant temperature the magnitude of adsorption physical adsorption increases initially and then becomes constant one the small thing you write down here which is not here factors affecting we are done see when you plot a graph write down one note here a plot of temperature versus pressure temperature versus pressure for a given amount of adsorption for a given amount of adsorption is called is called adsorption adsorption isoster so for a given amount of for a given amount of adsorption is called adsorption isoster okay so basically when you draw a graph between temperature and pressure for a given amount of adsorption the graph is called as adsorption isoster this adsorption isoster it is a straight line like this once they have asked question on to this like they have asked what is adsorption isoster so it is straight line graph drawn between temperature and pressure for a given amount of adsorption this you just keep in mind adsorption isoster okay like adsorption isobar when the graph is drawn excuse me drawn at constant pressure for a given amount of adsorption the graph of temperature and pressure is adsorption isoster okay and one more thing we'll see here that is adsorption isotherm this is most important out of the three write down the heading adsorption isotherm all these things we are discussing for adsorption of gas over liquid gas over solid where gas is what gas is adsorbent and liquid is adsorbent okay adsorption isotherm write down it is the variation of it is the variation of amount of gas adsorbed adsorbed with change in with change in pressure at a given temperature change in pressure at a given temperature okay the most important graph we have here and we call it as friendly adsorption isotherm write down this write down into this the graph of this the definition is this only the amount of gas adsorbed with change in pressure at a given temperature okay the graph here is this is x by m axis x is the amount of adsorbent m is the mass of adsorbent okay so this x by m is the is the amount of amount of the mass that adsorbed per unit mass of adsorbent is x by m and this side the axis we are taking as pressure so at constant temperature the graph that we draw here or we get like this like this friendly adsorption isotherm it gives us a relation of the amount of gas adsorbed per unit mass of adsorbent and pressure and this relation is given by x by m x by m is directly proportional to the pressure p to the power one by n it is just based on observation okay there is no proof of it the statement this is given by the scientist called friendlich where this n is n is always greater than one so one by n the value lies in this range zero to one okay and this graph is true only for this is option what is n n is the number like i said always greater than one number of what any number two three four anything so so for given uh physical option n will be defined right like for given me yes you don't have to actually calculate n but the point is the variation of the amount that adsorb per unit mass of adsorbent is not always directly proportional to pressure okay it is actually an observation okay like let me explain this first what we write here at very low pressure you can also you know discuss this at very low pressure it is found to be the amount that get adsorbed per unit mass of adsorbent x by m is found to be directly proportional to pressure okay and that is why you see here till this point till this point it is a straight line till here right it is a straight line so for this reason we define the relation as x by m is equals to some constant k into p but when you when you further increase the pressure okay the graph goes like this it makes a curve till here which looks like a curve here so for this graph what we can write for this reason x by m is found to be p to the power one by n and for this reason this since it is almost parallel to the x axis we have so at very high pressure what we can write x by m is directly proportional to p to the power zero which means it is independent of pressure so what we can say to conclude this discussion what we can say that at very high sorry at low pressure the mass that adsorb per unit mass of adsorbent is directly proportional to the pressure that we are using at moderate pressure at moderate pressure the relation is x by m directly proportional to p to the power one by n and at very high pressure at very high pressure the mass that adsorbed is independent of independent of pressure these three things you need to keep in mind take care one second let me know once you're done done okay right so this is the three thing they ask this question very direct friendly adsorption is important okay this is one of the thing that if you want to revise in the last five minutes this chapter you should go through this okay this is one of the thing the friendly adsorption is important you'll get some numerical question also into this okay these three condition you must remember another thing is if you when you have this for moderate pressure if you take log both sides then what happens we'll try to establish a relation between two at moderate pressure moderate pressure we can write x by m is equals to constant k p to the power one by n and when you take log both side log of x by m is equals to what one by n log p plus log k is it fine now can you tell me the graph of log of x by m and log p the graph will be like this it is a straight line yeah what is this distance log k log k the y intercept is log k and the slope of this line is what one by one by n sometimes they give you graph like this and they'll ask you what is the value of k what is the value of n all this is it clear yes okay one more thing that we have observed you know practically is when you draw a graph different different temperature all these graphs at constant temperatures we call it as adsorption isotherm okay constant temperature graph three different graphs we get here suppose one graph is like this the another one is this and one more it is around zero degree celsius this is around minus 29 degree celsius and this is minus 78 degree celsius okay now this x is x by m and this is pressure okay so for a given amount of adsorption okay suppose this for a given amount of adsorption this is the amount we have at this temperature minus 78 what is the pressure we have this pressure we have something suppose p1 and this pressure is p2 what you can conclude from this graph for a given pressure as temperature decreases adsorption increases temperature decreases adsorption increases adsorption increases for a given pressure one more thing i'll draw here this line you assume this line in this case we are getting different amount of gas that adsorb right so for a given pressure as temperature increases this is the temperature increasing right minus 78 to zero for a given pressure as temperature increases the amount of gas that adsorb decreases fine minus 78 degree celsius this is the amount of gas adsorbed for the same pressure minus 29 this is the amount of gas adsorb at zero this is the amount of gas adsorb the amount of gas that adsorbed at a given pressure right decreases with increasing temperature clear yes sir right and if temperature you are increasing for a given amount of adsorption this blue one i'm talking about if temperature you are increasing for a given amount of adsorption you have to increase the pressure also to maintain the same you know adsorption clear so on these two variations they may ask you theoretical question they may frame the question there are four options you need to think about it so best ways to keep this graph in mind okay and then you can conclude both the question you can do clear yes sir okay so this is the first part of this chapter we have adsorption adsorption we have discussed okay all these things that we have discussed i am not going to write this again i'm just giving you the similarity in this all these things that we have discussed so far it is the adsorption of gas on solid keep that in mind if you haven't written it write it down gas on solid we have discussed so far that's why we were talking about the liquefaction thing value of a and o okay similar thing we have when we consider the adsorption from solution phase okay adsorption from solution phase the only difference is what for a gaseous phase we have pressure in this this this thing that this uh expression contains this pressure when you are talking about the adsorption from solution phase initial of this pressure we have what we have concentration of solution is it clear adsorption on solid yes okay sir understood so write down this point adsorption from solution phase heading you write down just two three lines you write down we'll move on them adsorption from solution phase important one is this gas on solid okay but the similarity i'm just giving you write down the process of adsorption takes place from solutions also takes place from solutions also it is observed that it is observed that solid adsorbents solid adsorbents adsorb certain solutes adsorb certain solutes adsorb certain solutes from solution adsorb certain solutes from solution in preference to other solutes and solvents example you write down the litmus solution there are many things you must have done but you haven't observed this that is the process of adsorption example the litmus solutions when shaken with charcoal becomes colorless okay the example is the litmus solution when shaken with charcoal becomes colorless another example the precipitate of mg oh hole twice the precipitate of mg oh hole twice attains blue color attains blue color attains blue color when precipitate when precipitated in presence of when precipitated in presence of magnesium reagent m a g n a s o n magnesium reagent it is actually an indicator that we use not that important but it is a kind of indicator we use okay so the expression of adsorption the amount of adsorption in solution phase with respect to the friendly adsorption isotherm will write here x by m everything is exactly same will get k c to the power 1 by n where c is the concentration c is the concentration you know buttermilk yes sir buttermilk actually in villages what happens they used to sell this thing they used to know prepare this and sell per glass there are some 5 10 rupees is there so sometimes what happens the buttermilk if the amount of salt is very high or amount of salt is more over there to reduce the amount of salt into this they put two three pieces of coal into it in the mixture okay so that coal adsorb the solute that is adsorb the salt which is present into that buttermilk and hence the amount reduces and the test is comparatively better so that's solid on solid adsorption right yes that is sorry i'm giving i'm just giving one example that is solid and solid even in that's a part like you used to say when you cook something right and if the amount of salt is more by mistake you put one two three pieces of coal into it that will reduce the amount of salt and 30 is to put potatoes for it to adsorb potato is the potato we have starts present into that no so it produced some sweet to that uh mixture in so in that way the you know the amount of salt won't reduce but it gives some sweetness to the test no that's why it feels like amount of salt is left but there is an example actually that when you put that coal pieces into that uh buttermilk right so that coal pieces adsorb salt from that buttermilk and hence it reduces the amount but that's a different thing i'm just giving you this example so that you can correlate and keep that in mind okay so all these are examples of adsorption so anyways two three things are there friendly adsorption iso some of the most important whatever we've discussed so far okay they ask questions onto this numerical they may ask you onto this line graphical based question they can ask okay difference of physical and chemical adsorption is also important okay like i said multi-layer unilayer and you know the pressure relation reversible irreversible many things in board also they ask that what is the difference between physical and chemical adsorption all those things are important now the next thing we are going to discuss here is colloids what is this what are colloids you don't know i'll take here three different uh mixture one two and three in this three beaker i put water into it all these are h2o h2o h2o okay so what i do here i put salt nacl into it here stand and here mill what is the difference in these three in this solution what happens after sometime when you put salt into it it you you look at this solution you won't see any salt particles present into it because it dissolves completely okay here what happens if this becomes muddy right you can see the violet colored over here and this you cannot even see you cannot even understand that there is water also present into it when you mix mix this wilkin into it the point is these three are three different kinds of mixture we have okay so to understand colloids we have to understand first what is a true solution and from true solution how do we get colloids and then how do we get suspension okay to understand this colloid and suspension okay true solution is what true solution is defined for homogeneous mixture yes or no that we have discussed already yes the water and nacl forms homogeneous mixture homogeneous mixture are those mixture in which there is only one phase present and that is when you mix nacl into it you can see only water present into it and hence we can say only one liquid phase we have here only one kind of phase present mixture is homogeneous but that is not true into these these two cases okay here we have sand plus water and this another thing you can understand like for uniform concentration just tell me one thing you have one solvent here say water and when you put very small amount of solute into it which whose size is also very small when you put into this and in the second case you have you are increasing the size of the solute particle that you are putting in so what happens with very small size okay that tendency to get settled is less or more suppose i am taking two examples here both beaker has water present into it okay and here i have put two solids into it with very small size and here the size of solute particle is like this if i ask you in which of these two mixture the tendency to get settled is more the second one right the one right and why this settling takes place because as size of the particle increases the force of gravity also increases onto the solute particles and hence it has more settling tendency okay here what happens when the size is less force of gravity which acts onto this particle is also less and the liquid molecules the solute the solvent molecules that you have that also you know collides continuously with this molecule in all direction because of this collision it keeps on moving here and there in the mixture and hence the tendency to get settled is very less and that is why there are high chances for this mixture that it may form a true solution which is a homogeneous mixture but if i ask you whether we have the tendency for this mixture to form a homogeneous mixture the chances will be less because the size of the particle is less and it has more force of gravity experience and hence the tendency to get settled down is more over here right so what is the difference in these two mixture is the difference between the size of the solute particle okay so we must have a range of the size which forms a homogeneous mixture and then it when it settles down it forms another kind of mixture and then when again if you increase the size it gives you another kind of mixture so based on the size of the solute particles the mixtures are classified into three categories one is true solution next one is collides and next one is suspension okay so write down next thing here that based on the size of the solute particles based on the size of solute particles the mixture has tendency to form the mixture has tendency to form homogeneous or heterogeneous mixture right and on this way we define three types of mixture one is solution that is true solution and then when you increase the size of the solute particles it forms collides further if you increase the size it forms suspension so for solution the size of the particles must be less than one nanometer then it has high tendency to form homogeneous mixture homogeneous mixture when the size of the particles solute particle is less than one nanometer collides forms when the size of the particle is greater than one nanometer but less than hundred nanometer in this range of solid particles colloid forms for suspension the size is greater than hundred nanometer this is for suspension okay so when the size it is observed that when the size of the particle is more than hundred nanometer then the force of gravitation dominates and hence the settling takes place it settles down okay so we are now trying to put focus on collides okay we're trying to understand this collides the definition of collides you write down a colloid is a heterogeneous system i'll write down here it is a heterogeneous system heterogeneous system in which one substance in which one substance in which one substance is dispersed dispersed as very fine particles particles of another substance particles of as very fine particles of another substance another substance called dispersion medium it is a heterogeneous system in which one substance is dispersed as very fine particles of another substance called dispersion medium this is again as very fine particles in another substance not off sorry in another substance called dispersion medium so if you compare this with solution okay solution uh if you do this comparison solution there are two components one is solvent other one is solute okay similarly in colloids we have dispersion dispersion medium dispersed phase dispersed phase if you try to compare this with solution so solvent is equivalent to dispersion medium in colloids and solute is equivalent to dispersed phase in colloid got it okay so whenever we discuss about heterogeneous system then we won't use the term called solvent and solute but we use dispersed phase and dispersion medium dispersed phase and dispersion medium correct now you see like solutions are classified into nine different categories depending upon depending upon what the the phase of the solute and solvent like it may be solid liquid and gas like that okay so similarly this uh colloids are also classified into different categories depending upon the physical state of dispersed phase and dispersion medium okay so next heading you write down classification of colloids classification of colloids and this classification is based upon based upon the physical state of dispersed phase dispersion medium and dispersion medium okay so i'll draw a table here all of you draw this table we have dispersed phase dispersed phase and we have dispersion medium name of the colloids and then some example dispersed phase okay dispersed phase can be solid it can be liquid and it can be gas now when dispersed phase is solid dispersion phase okay so if this phase is solid phase means what the it is equivalent to uh solute over there medium can be solid can be liquid and can be gas solid plus solid the name of the soul that we have here we call it as the solid plus solid the name of the colloid that you get here its name is solid stone the example is gemstones we can you we can write we can also write some colored glasses gemstones colored glasses solid plus liquid we call it as soul this one is important this one is important soul solid plus liquid is soul example is we have glue starch we can have paints solid plus gas the name is aerosol and its example is smoke dust liquid with liquid we can have this has as solid so liquid plus solid we call it as gel liquid plus solid we call it as gel example is cheese butter etc liquid plus liquid the name is emulsion any example of emulsion liquid with gas there is paint and emulsion paints is an example of soul in ncrt paints they have given as emulsion in ncrt i guess paint should follow sorry which one should we follow i think because when you read some higher books paints is an example of soul okay it's not an emulsion so i think in school exam better you should follow i think you should follow ncrt only school exam you should follow ncrt only don't write paints as in soul solid plus liquid plus gas liquid plus gas the name is what name again we call it as aerosol liquid plus gas the example of this liquid plus gas aerosol is cloud fog mist that foam right foam is not foam is a this thing um foam is a gas in liquid okay foam is gas in liquid gas with solid we call it as solid foam solid form example of gas in solid we have okay gas in solid solid soul you write down not it is solid soul solid soul example is humic stones humic stone you can take foam rubber gas with liquid is foam example is leather cloth gas plus gas this form is not possible because this gives a homogeneous mixture homogeneous mixture okay so in this soul and this emulsion you must remember okay this is the classification of colloids based upon based upon the phase of dispersed phase and dispersion medium okay second type of classification which is again important and that you write down classification based on the nature of interaction all of you done this yes sir yes sir so now we're doing classification based on i'll write down classification based on the second type based on interaction between interaction between dispersed phase and dispersion medium how much more left there are few things we need to understand here today we'll finish this push on it's theory dude i think that was niranjan not me niranjan okay yes sir yes okay write down quickly write down depending upon the nature of interaction colloids are classified into two categories colloids are classified into two categories can you tell me the first one have you heard about lyophilic yes sir what is lyophilic uh favorable oils and basically non not water non is it non polar lyophilic colloids are those colloids which are attracted to what's the dispersion medium that's what is lyophilic another one is lyophobic okay so definition of this you write down these are the colloids these are the colloids which are attracted towards the which are attracted towards the dispersion medium dispersion medium means what it is equivalent to solvent that we have in solution dispersion medium write down these colloids can easily be formed these colloids can easily be formed by mixing of substance like by mixing of substance like by mixing of substance like gum gelatin no wait did you see gum like the chewing gum uh no not that gum that glue glue glue idea yeah i think anyone asked you okay gum uh what you write gelatin starch rubber etc sorry starch rubber in a suitable liquid in a suitable liquid see there are two things uh lyophilic like i said and other one another one is lyophobic okay lyophilic and lyophobic lyophilic colloids we don't have to do anything just you need to mix the the substance with the suitable liquid you'll get lyophilic colloids okay but lyophobic colloids it's not very easy to you know to get this lyophilic colloids we have some preparation method we have to have some add uh some different uh you know substance into it so to understand this lyophilic like as far as the importance is concerned lyophilic colloids are not that important lyophobic is more important okay so the next one you write down the next line in this the important properties of these souls the important properties of these souls means lyophilic colloids or lyophilic souls is the dispersion medium can be separate out the important properties of these souls is that the dispersion medium can be separate out from the dispersed phase by evaporation and hence it is reversible soul you got this point and hence it is reversible soul means what suppose gum and or starch if you put into uh any other liquid like suitable liquid the thing we have to keep in mind that the size must be in the range of colloidal solution which forms a colloidal solution right if that size is there starch you mix with liquids it forms a lyophilic colloids when you heat this little bit the dispersed phase and dispersion medium can be separated out easily okay and when you again mix this you'll get colloidal solution lyophilic colloidal solution so this thing is what this thing is reversible in nature okay so lyophilic colloids are reversible in nature this is one very important point we have here the next one you write down lyophobic colloids the second one lyophobic means what liquid which hates liquid okay so lyophobic colloids are not attracted towards the dispersion medium lyophobic colloids are not attracted to what these are the colloids which are not attracted towards the dispersion medium hence to prepare this hence to prepare this we have to use some special method we have to use some special method these colloids next line write down these colloids are easily precipitated are easily precipitated by addition of a small amount of electrolytes comma by heating or by shaking can you repeat what I said that these colloids are easily precipitated by adding by adding small amounts by adding small amounts of electrolytes by heating or by shaking and hence these are not stable okay these are not stable next line once once precipitated once precipitated they do not give back the colloidal solution they do not give back the colloidal soul by simple addition of the dispersion medium once precipitated they do not give back the colloidal soul by simple addition of dispersion medium hence they are irreversible souls hence they are irreversible souls okay so lyophobic colloids since these are not attracted towards the what towards the solvent or dispersion medium so we cannot mix the dispersed phase and dispersion medium to get these kind of colloids because the mixing is not possible okay to get this kind of colloid we have to have some special method of formation of this and that will discuss the preparation method of colloids okay difference you must know okay the first one lyophilic is reversible this one is irreversible the another difference if you see the viscosity of lyophilic skull is much higher than the viscosity of lyophilic skull is much higher than the viscosity of dispersion medium okay but in case of lyophilic colloids the viscosity is almost similar to that of the dispersion medium okay the lyophilic is higher lyophobic is higher lyophobic is close to the dispersion medium okay coagulation you know what is coagulation precipitation coagulation is the precipitation you know right the precipitate forms the same thing is coagulation also coagulation and flocculation I'll write down this thing later on okay lyophilic colloids are quite stable okay so write down just one last point in these two the precipitation of lyophilic colloids is difficult the precipitation of lyophilic colloids is difficult but that of lyophobic colloids is easier okay so this is the two classification we have based upon based on the interaction between the dispersed phase and dispersion medium okay one last type of classification you see the third one which is classification based on the type of particles present type of particles present in this we have three types of classification the first type we have I won't give you much theory into this okay it is not important the first two multi-molecular colloids just one line you write down into this multi-molecular colloids this forms when large number of atoms this forms when just one line you write down large number of atoms atoms or smaller molecules the size must be smaller see types of particle present so we are considering the size of the particles here overall the size must fall in the range of colloidal particles okay smaller molecules aggregate aggregate to form species to form species having size in the having size in the colloidal range colloidal range this is one thing not important at all i'm just uh moving off example just example write down sulphur soul sulphur soul consists of sulphur soul consists of thousand s8 s8 sulphur molecules s8 sulphur molecules this is multi-molecular colloids the second one in this we have macromolecular colloids macromolecular colloids okay in this the substance having large molecules okay so large molecules are dissolved in are dissolved in suitable liquid are dissolved in suitable liquid right this is the condition the suitable liquid condition is what overall that the size must fall in the colloidal range okay example of this is you know there are two things one is naturally occurring and other one is synthetic so naturally occurring macromolecular colloids are just example you must keep in mind this is them like i like i said it is not at all important okay starch cellulose protein enzymes starch cellulose proteins and enzymes are natural occurring synthetic one synthetic one is write down nylon rubber polythene etc nylon rubber polythene etc can you go to the next page yes sir yes okay one second one second yeah okay the third type t here which is important and that you must have heard about this associated colloids have you heard this associated colloids no have you heard this missiles missiles you must have heard right yes sir yes sir okay okay right or into this there are some substance there are some substance which behaves as this the third one is important okay which behaves as and behaves as a strong electrolyte electrolyte at low concentration low concentration but as concentration increases concentration increases this shows this shows colloidal property colloidal property behavior since they due to you know due to formation of due to formation of aggregates okay due to formation of aggregates this aggregates particles when this they combines together this aggregates particles are called missiles associated colloids now you see there are two things into this this you must remember only definition you have to memorize there are two things like formation of missiles due to formation of aggregates which is known as missiles write down the last thing which is known as missiles formation of missiles takes place won't take place at all temperature for that you must have one temperature you must have you know you the the whole process to form missiles you must have one minimum temperature okay so the two condition we have here that is temperature minimum temperature must require and minimum concentration also must require because what I said here no concentration it is an electrolyte but when concentration increases it behaves as in colloids missiles so what is that minimum concentration the minimum concentration we call it as CMC CMC write down it is critical missile concentration it is a minimum concentration above which above which aggregation takes place critical missile concentration CMC it is the minimum concentration above which aggregation takes place the minimum temperature we need here and that temperature we call it as craft temperature have you heard about this craft temperature that we write it as Tk it is a temperature sir can you repeat what the full form of CMC is critical missile concentration yeah craft temperature write down the formation of missile takes place above a particular temperature and that temperature is and that temperature is craft temperature okay sir if there's a lot left can we have a break small one you won't break now yeah there are things left into this we have to discuss anytime convenient you can give break can you give a break now my back is hurting for a wrong class this is not physics oh god see what tell me sir you given you want to get some time sir okay we'll take a break we'll start at 430 thank you fine can you just repeat that last point about craft temperature craft temperature is the minimum temperature above which the formation of missiles takes place CMC critical missile concentration there's a minimum concentration above which again formation of missiles takes place yes i got it thank you sir okay take a break 430 we'll start guys can we start yes sir yes sir okay so we discuss about the missile formation right see actually uh in missiles what happened uh how this missile forms the mechanism we have for example the soap we take right soap is nothing but what soap is the sodium or or potassium salt of potassium salt of higher fatty acids higher fatty acids for example if you take this uh the molecule formula C17 H35 POO minus Na plus this is the formula of soap okay now in water what happens this exists in the form of ions okay POO minus Na plus will be out so this exists this way suppose we have this CSP CSP and last we have here P double bond OO minus yeah i'm just uh no i'm writing this to make you understand okay this C17 S35 will be here and this is the ion you can this part CO minus we call it as hydrophilic part hydrophilic why i'm calling it as it is same as liophilic liophilic term we use when the solvent is not water okay when the solvent is water liophilic becomes hydrophilic right this is polar also so polar one is attracted towards the water molecule hydrophilic this one is non-polar and this part is hydrophobic okay we also call it as hydrophobic tail and this is hydrophilic head got it okay can i go to the next page yes so this soap has actually two part of it one is hydrophilic other one is other part is hydrophobic okay so when you put this into water okay so water we have suppose this thing so the hydrophilic part is into the water like this and hydrophobic part is out of the water means away from the water molecule away from the water molecule so i should write this as it's not a straight line this way again we have negative negative this all this negative thing is hydrophilic and this is hydrophobic part okay at cmc what happens cmc is what critical missile concentration at cmc all these anions are pulled into the bulk of the solution and they aggregate to form a spherical shape okay at cmc critical missile concentration anions are anions are pulled into the bulk of the liquid into the bulk of liquid and forms and forms a spherical spherical shape and forms a spherical shape with their hydrophobic part is pointing towards the center of the sphere a spherical shape in this the hydrophobic part hydrophobic part towards the towards the center of the sphere and then it then forms a missile so missile formation is this only so we have the diagram if i draw off it is like this this is the spherical shape we have here and all these ions okay it is this is the hydrophobic part pointed towards the center of the sphere all this is c o o minus c o o minus c o o minus c o o minus c o o minus c o o minus c o o minus c o o minus c o o minus okay so this alkyl group or the hydrophobic part it's pointed towards the center of this sphere and this we call it as missile or ionic missile okay the hydrophobic part it it has affinity towards the oil droplets or grease molecule that you have that dust whatever it is there so how it works because it is a soap right so we know the fabric has cross linking of polymers like this we have supposed in the fabric we have cross linking like this suppose we have some oil particles or grease particles here at this or any point we are here we have so what happens this missile this missile the hydrophobic part makes a bond with this oil or grease particle that you have here so around this what happens around this the hydrophobic part is towards this oil droplets that you have it surrounds like this like this here we have c o o minus c o o minus c o minus everywhere we have okay it makes a bond with this oil droplet and hence finally what happens with the cloth it takes this oil particles or oil droplets with it and washed away with the water okay with water that's how it works in the cleansing this is actually the cleansing action of soap okay basically you need a minimum amount of dirt to be washed away not minimum amount minimum if the dirt amount is less than you required less amount of soap or detergent even detergent also works in this way see you must have seen this if the clothes are very dirty you required more detergent to clean that okay if the number of clothes are more than it with with you know with in that ratio only required the amount of detergent okay so that's how it works basically it forms a missile and the hydrophobic part has affinity towards the oil droplets grease or dirt that you have just that you have there in the clothes it makes a bond with this oil droplets or grease and then it wash away with the water molecule okay in one missile these kind of missile it actually contains 100 such ions 100 such ions got it can we go to the next page yes sir okay formation of colloids like i said preparation of colloids there are two three methods we have for the preparation of colloids one is dispersion method other one is condensation method there we have exchange of solvent and all dispersion method there are one two things which are important okay dispersion method so it does write down preparation of colloids heading you put preparation of colloids the first one is mechanical disintegration mechanical disintegration in this what we do see whatever colloids we have to prepare okay it actually carries out in a machine called colloid mill okay in colloid mill what happens it consists of two disc steel disc okay and there is a gap between the two discs okay and they can rotate in an opposite direction you can assume one disc on the top one disc on the bottom there is a bit of space between the two discs and both are rotating in the opposite direction okay so we need to disintegrate the molecules and we have to get the size which is required for the collusion colloidal particles okay so our objective is what we have to disintegrate the molecules and get the size which is required to get the colloidal solution and to reduce the size we are using this colloidal mill right so what happens this disc is rotating in a very high speed okay now the solid material with which if you want to form the colloid that material will put into the gap between the two discs and the disc is rotating in an opposite direction so that so the solid particle that you put in it dissociates or disintegrate into the smaller particle okay and then we'll mix this with a dispersion medium right dispersion medium and we also add a stabilizer into this mixture which stabilizes the colloidal solution okay so right down into this we have this colloidal mill okay the solid particles write down the solid particles or material the solid particles or material is disintegrated with the help of colloid mill and then mixed with the dispersion medium so can you repeat the solid the solid material is disintegrated with the help of colloid mill and mixed with the dispersion medium to get the colloidal mixture to get colloids next line a stabilizer is often added to stabilize the colloidal solution okay but this method is not that useful the another one and the important a bit more important is the electrical disintegration this is mechanical disintegration here we have electrical disintegration and electrical disintegration we use the we use actually the potential difference we have to have a we'll have a electrode and that will connect with the pd for result we have we will connect with the with the voltage source basically electrical disintegration this rule we also call it as this method we also call it as bradyx arc method just two three lines you write down here bradyx arc method this method is used for the preparation of method is used for the preparation of preparation of colloidal solution of metals like colloidal solution of metals like silver gold platinum etc silver gold platinum etc okay what we do into this method that will do the we use the method of electrolysis actually the metal of which the colloidal solution has has to prepare okay we'll take that as an electrode for this purpose and corresponding to that we'll take the dispersion medium also here so this is connected to the external voltage source right and suppose we have to form silver colloids right so we'll take silver rod as the electrode here okay what we do when we connect with the high voltage source right it gives a very high amount of electric arc here electric shock you can say it produce so because of that some metal elements here the silver elements here it get vaporized okay because of that high electric shock you can say or electric arc you can say the metal elements here silver elements get vaporized okay and since it is it is kept into the cold water here chilled water also we use this is chilled water or cold water you can say okay so when it vaporize it is dipped into the water okay so as soon as this vapor silver vapor comes into the contact of this chilled water it get condensed and that gives you the colloidal solution here okay so what happens due to electric arc write down quickly into this due to electric arc electric arc some atoms some metal atoms converts into into gaseous form gaseous form and when it comes into the contact of chilled water it get condensed and when it comes when it comes into the contact of contact of chilled water it get condensed and that gives the colloidal solution of that metal one thing you must keep in mind that metallic sol means when you prepare a sol with metals metallic sol are negatively charged this charge you must have to keep in mind this is the most important part of this are negatively charged i'm coming to this charge part the charge thing now but you have to keep this in mind that metallic sol are negatively charged always because when it comes forms the vapor and then it condense it grabs some electrons also into this that's why it becomes negatively charged okay this is predicts arc method predicts arc method how to form colloidal solution that we are discussing but all of this the most important part is that the metallic sol are negatively charged okay there's one more method of preparation we have of colloids okay third one which is the most important out of the three the third one is peptization peptization it is defined as the process of process of converting a precipitate converting a precipitate freshly prepared precipitate into colloidal sol into colloidal sol so from precipitate we are trying to prepare the colloid in this method so for that what we do we and for this purpose we use an electrolyte i'll write down this in a symbolic way we'll use an electrolyte electrolyte which has one common ion which has one common ion so suppose for example if i take the precipitate as agi so from agi precipitate if you try to form colloidal sol then in this you have to mix one electrolyte which has at least one common ion okay so what we can do in this two way we can prepare the sol into this we can either use agn o3 or we can also use ki is it clear agn o3 either we can mix agi with agn o3 or we can mix agi with ki these two are electrolyte okay and to and in peptization the process like i said what is the process is the process of converting a precipitate freshly prepared precipitate into a colloidal solution okay and to do that we use an electrolyte the condition of electrolyte is what it must have one common ion so agi is the electrolyte suppose then we can take agn o3 as an electrolyte or ki as an electrolyte is it clear yes sir okay so what happens here you see the the property of this the electrolyte that you have the sorry the precipitate that you have agi okay it gets surrounded by the common ion here the common ion if you add agn o3 is ag plus so it is surrounded by ag plus like this ag plus ag plus ag plus ag plus and ag okay and this finally disintegrates into the colloidal range disintegrate into the colloidal range because for colloids we must have the range of the particle size must be there in that range okay disintegrate in the in the colloidal range and we get a colloidal solution here when you add ki into it then what happens will have agi precipitate and it is surrounded by what surrounded by i i minus i minus it is always surrounded by the common ion that you have i minus i minus i minus and i minus and finally in this also the same thing happens it disintegrate in the colloidal range right but when you add agn o3 and ki the charge of the colloidal solution is different since it is surrounded by the positive charged ion it is positively charged positively charged colloid and this is negatively charged colloid okay understood this this is the most important part of the of the entire colloidal discussion that we are doing negatively charged colloid or negative colloid is it clear tell me fast we don't have that much time we'll go a bit faster yes it's clear okay collides are i'm going towards the next thing see whenever you prepare like this or this is the peptidation method we have discussed even method is something else then because of some you know of collagen between the dispersion phase and dispersed dispersed phase and dispersion medium all the colloid particles will definitely have some charge okay it is always there thing is what the two points you need to memorize or keep in mind the colloids are colloids are always charged there will be some charge and it is not like positive negative both charges present it will be either positive or negative okay and we say why does Sravan become the host every time so uh so wait now what do we do he just takes the two minutes wait the governor the giant is not gonna say hey admin you a host you should know i just said better all hey Sravan what all can you do as host uh i can share screen and that's it i can't do anything extra even i can share screen yeah but yeah you can i can record what are we doing dude is his uh laptop day Sravan share your screen and show us what you're watching right now nothing i'm watching you're watching the thing i can even unmute people oh yeah the rich sir always does that so are we just gonna like sit here where do you have to go uh make me the host sir he's dying okay so the problem is if i leave it make someone else the host i don't know who it will make but i'll leave and show you i okay go ahead you know you can make someone the host yeah you can who's always a host you can you know make anyone the host anyways so we were discussing what we were discussing uh colloids are always charged okay when i say colloids are charged i am talking about colloids particle okay colloids particle means what dispersed phase not medium dispersed phase not medium okay all these colloid particles are either positively charged or negatively charged okay either positive or negative it cannot it is not possible that two three particles are positively charged and two three particles are negatively charged both not possible either positive or negative okay that's why you see this colloids are we also say that they are stabilized by repulsion or by repulsive force so right on the next thing colloids are colloids are stable through repulsion what do you mean by this stable through repulsion suppose you have a colloidal particles here in this vessel we have liquid molecules and colloidal particles and in this colloidal particles we have some colloids particles present which are supposed negatively charged okay negatively charged first of all the size is not that enough so that these particles get settled okay and since they are negatively charged so they repel each other continuously in all direction all these particles are repelling each other continuously in all direction that's why they move in zigzag manner in through the entire solution okay the reason is because of charge they are repelling each other hence they are moving here and there in zigzag motion second thing we'll have collision between the dispersed medium and dispersed phase also and that's why they continuously move entire in in in all direction okay and this movement we call it as Brownian movement okay so this is the property of colloids they have Brownian movement Brownian movement means what they'll move like this randomly in any direction this is Brownian movement okay why they are stable through repulsion because negative negative or positive positive charge repel each other that's why they are continuously moving into solution into the mixture and hence they are not getting settled understood this yes sir okay yes sir one thing you must take care of in peptidization the electrolyte that you are using that must have one common ion that is very very important if common ion is not there then colloid solution won't form okay now the thing is supposed by any means if you destroy this charge I'm moving to the next point if you destroy this negative charge then what happens then there won't be there is not any Brownian movement there won't be any repulsion right and then it started it is it starts settling down okay that is one property we have there but when charge is not there repulsion won't be there and they have tendency to come closer and aggregates are you getting it so none of this will happen if common ion is not there no what a first the first thing is what peptidization for peptidization we need an electrolyte which has a common ion so you get collides now okay and we know collides are stable through repulsion okay and why repulsion is there because colloid particles have same charge same kind of charge positive at the plus plus plus plus two at the plus two plus two plus two minus two minus minus minus minus two this so when you destroy this charge charge on the colloidal particles if you destroy this then all these colloidal particles have tendency to come closer are you getting it because there is no repulsion now so all these particles have tendency to come closer and they aggregates forms a large particle and that actually destroys the colloidal property of the mixture is it clear tell me yeah sir yes sir so when the charge when you destroy charge particles come closer aggregate the mass increases hence force of gravity also increases and hence there will be a tendency of settling correct this settling of charge particle we call it as coagulation flocculation or precipitation is it clear right when this coagulation precipitation or flocculation all three things are same right so write down the heading coagulation precipitation and what flocculation i'll write down it three terms we have which are the same thing coagulation precipitation or flocculation flocculation write down into this quickly write down that stability of liophobic souls the stability of liophobic souls is due to the presence of charge on colloidal particles the stability of liophobic souls is due to the presence of charge on colloidal particles hence sorry since all the colloidal particles since all the colloidal particles are considered to have the same charge same kind of charge even in magnitude also they have equal charge same charge hence they are stable through repulsion hence they are stable through repulsion by any means if the charge is removed by any means if the charge is removed the particles comes closer to each other comes closer to each other and form aggregates and forms aggregates forms aggregates and eventually this starts settled down due to the force of gravity and eventually this starts settled down due to the force of gravity okay due to the force of gravity next line the process of settling of colloidal particles is called coagulation the process of settling of colloidal particles is called it's called coagulation okay it's called coagulation understood this coagulation yes now this coagulation is possible by two three ways you don't have to don't need to go into that detail only one thing is important here that we'll see the first method by electrophoresis we can achieve coagulation by these four methods electrophoresis r e s i s electrophoresis in this what happens there is actually uh we we introduce a two electrode into it and then when you apply potential difference okay there will be movement of charged particles towards the opposite charge electrode okay electrophoresis is the phenomenon of movement of colloidal particles under an applied electric field okay so if you have the colloidal particles present in this vessel suppose positively charged or negatively charged whatever it is if you take an electrode here apply with a potential difference okay if it is negatively charged then it starts moving towards the positive electrode like this and it's accumulates here and hence the you know the coagulation takes place because a charged particle won't be there in the solution so electrophoresis not at all important the point is it is a phenomenon in by which when an electric field is applied in a colloidal solution then the charged particles present in the colloidal solution it starts moving towards the opposite charge electrode and hence the colloidal property is lost of the solution electrophoresis is this another way if you boil if you boil by boiling a lidon boil colloidal solution again you can achieve coagulation the third one is boiling we have done or suppose if positive charge colloid we have so by mixing of oppositely charged colloids by mixing of oppositely charged colloid did you understand these three yes charged collides if you mix opposite charged collides then they'll cancel out each other and there won't be any charge present and then it starts settling okay the most important method we have to achieve coagulation precipitation or flocculation is the addition of electrolyte on this they ask question in the exam addition of electrolyte so tell me if you have positively charged colloids okay then we need negative charge to destroy the positive charge our objective is to to achieve coagulation we need to destroy the charge present in the colloidal particles so if positive charge is there so we need some negative ion to destroy the charge if negative charge colloidal particles we have then we require positive charge to destroy the negative charge okay now to understand this we have a rule that we call it as hardy h a r d y hardy sol j rule s t h u l g z e hardy sol j rule according to this rule what we say that one simple thing you need to keep in mind it's very easy that you can easily understand it greater the valency of active ions right down greater the valency of active ions active ions we also call it as flocculating ion flocculating ions means what the ion that we are using took for the for this process coagulation flocculating ions greater the valency greater will be the coagulating part is it clear sir these ions are those that we add to the colloid right yes to destroy its colloidal property okay understood okay so can you tell me negative charge colloid if you have so we need positive ions to destroy the colloidal property correct so if i give you these three ions can you tell me the order by which they can destroy the post the colloidal property suppose we have k plus suppose we have m g 2 plus and a l 3 plus which of these ion provides maximum coagulation k plus a l 3 plus more valency more will be the colliding coagulation coagulating tendency so negative charge colloid if you have then a l 3 plus will destroy more this is the order of coagulating nature so just like magnitude of chance right yes yes magnitude only more positive charge more coagulation amongst a l 3 plus and then what's the next one there gallium something like that gallium is the same group no see you don't have to think much here only you see the valency that is what hardy sulje rule so what about n plus k plus uh cs uh rb plus etc see any plus k plus will have the same part it's just no no no we are just looking at the magnitude of it simply in you know layman language what you can say one positive charge will neutralize only one negative charge the two positive charge we need to utilize three will utilize three like that so if you have a positive charge colloids and i'm giving you suppose three ions which is suppose c l minus we have so for two minus we have and p o for three minus then which one will give maximum coagulation p o for p o for three minus right clear yes yes you just need to check huh you just need to check the magnitude of the charge over there okay but the thing is if you do not know what is the charge on colloid then how can you decide whether you have to take positive ion or negative ion are you getting me used to select these ions because they'll ask you this which will produce maximum coagulation okay they'll give you one soul suppose they'll give you a hydroxide soul okay fe o h whole thrice or suppose they'll give you metal sulphide soul like the question is for metal sulphide soul which of these ion will use for coagulation you should first know what is the charge on metal sulphide are you getting me okay so this part you need to memorize okay there are some general trend i'll give you like the positive charged soul first one you write down positive charged soul this one again very very important the coagulation power and all very important hydrated metal oxide you have hydrated metal oxide this much you remember you can do all the questions first condition is this hydrated metal oxides are positive charged soul for example if i give you fe two o three dot x h two o hydrated metal oxide positive charged soul if you have cr two o three dot two h two o hydrated metal oxide positive charged soul human blood human blood is also positive charged slope third one is ti o two it is also metal oxide positive charged flow negative charged soul negative charged soul is metal sulphides all metal sulphides are negative charged soul like as two s three metal sulphides souls of heavy metal like i said silver and all souls of heavy metal metal souls are negative charged souls colloids souls of starch gelatin etc so this two three information you must have which one is positive charge which one is negative charge once you know this charge of the soul you can easily find out which ions we should use positive ions or negative ions to destroy the colloidal property okay now if the order is given more positive ion more positive charge more will be the what we say coagulating tendency okay yes sir now the next thing in this because uh when you boil the colloidal solution it loses its colloidal property right to protect colloidal property what we should do so next heading you write down protection of colloids protection of colloids see for protection of colloids what we do liophilic souls actually liophilic souls are more stable more stable than liophobic because what happens in liophilic souls you have an uh electrolyte here and it is surrounded by the water molecule because it is water lovers so these are surrounded by the water molecules and when it is surrounded completely all those charged species won't have that the capability to attack onto this uh colloidal particles and destroy it okay so this is liophilic since it has a layer of water molecule here water molecule or you can say dispersion medium layer we have here okay so because of this layer and why this layer is there because it is liophilic attractive attracted towards the towards the um um dispersion medium okay so this we have a layer of dispersion medium here that's why the electrolyte has very less tendency or electrolyte is not enough powerful so that it can penetrate this layer of dispersion medium and then destroys the colloidal particle here that's why liophilic souls are more stable than liophobic now to make this stable to reduce the coagulation what we do we add liophilic salt into the liophobic soul okay so right down into this since liophilic souls are more stable hence we can add liophilic salt hence we can add liophilic soul to the liophobic soul to the liophobic soul to protect its colloidal properties to protect its colloidal properties so what happens into this next line right down the particle of liophilic soul the particle of liophilic soul surrounds the particle of liophobic soul surrounds the particle of liophobic soul hence coagulation becomes difficult then hence the coagulation becomes difficult and that is the reason liophilic soul is also known as protective colloid am i clear with it so can you repeat the first line once i'm sorry what is the first line the particle of liophilic soul surrounds the particle of life that's one yeah the particle of liophilic soul surrounds the particle of liophobic soul hence coagulation becomes difficult yes sir thank you sir okay now there is one more there is one more term here the last thing we have to discuss here is how to find out the strength of protective colloid we should know that which colloid is what is the strength of each and every colloid so that we can use according to their strength okay so strength of protective colloid write down this heading protective colloid okay the strength of protective colloid to determine the strength will use a term and that we call it as gold number okay it is the number of write down the definition of gold number all of you it is the number of milligrams of protective colloid it is the number of milligrams of protective colloid that will prevent the coagulation of that will prevent the coagulation of 10 ml of a gold soul that will prevent the coagulation of 10 ml of a gold soul on the addition of on the addition of one ml of 10 percent NaCl solution wait wait coagulation of 10 ml of gold soul on addition on the addition of one ml of 10 percent NaCl solution okay the reference is gold soul definition you again go through it is the number of milligrams of protective colloid that will prevent the coagulation of 10 ml of a gold soul on addition of one ml of 10 percent NaCl solution okay if i give you one protective colloid suppose we have protective colloid one protective colloid two for this for this protective colloid the gold number we have and which is 10 milligram is the gold number for this the gold number is 20 milligram can you tell me which one is a better protective colloid should one right the one the first one why because it needs it requires less of mass right less mass so it is this one is a better place less mass you require it means it has more you know power that's why the first one is a better protective colloid okay there are some molecules for which the gold number is given i'll just write down here you copy it down the first one we have gelatin its gold number is 0.005 to 0.01 hemoglobin 0.03 milligram egg albumin egg albumin 0.08 to 0.10 potato starch is 25 the worst starch 25 to 50 where the difference between potato starch and normal starch yeah even if it's about okay this thing you have to memorize now there's last few things we have to discuss is so we have to memorize all these no not like just you have this idea of like hemoglobin is a better you know gold is a better protein colloid than l albumin okay gelatin is also even better than this okay so at least two three like this some you know comparison you know value don't memorize because you never know i have seen this question in need exam they have asked which one is the best protective colloid like that they have asked okay that's for that purpose i have given yes but j e they are less chance that they'll ask this okay yes so last thing we have to discuss here is a tindal effect what is tindal effect it is the optical properties see brownian movement that i gave you is the mechanical property of colloidal solution okay optical property is the tindal effect write down this heading t y n d a double l tindal effect it is the optical property tindal effect is nothing but the scattering of light write down it is the scattering of light by the colloidal particles in a colloidal solution it is the scattering of light by the colloidal particles in a colloidal solution okay this is the question that they asked so far what is tindal effect one of the option will be scattering of light done but little bit more we'll discuss here next time you write down if a strong beam of light is passed through a colloidal solution a strong beam of light is passed through a colloidal solution placed in a dark place placed in a dark place the path of the beam gets illuminated the path of the beam gets illuminated so can you repeat this if a strong beam of light is passed through a colloidal solution placed in a dark place the path of the beam gets illuminated this illuminated path is called tindal cone this illuminated path is called tindal cone you must have seen projector right yes sir so in the dark room when the project when the when the projector if you see the light coming out from the projector you can see the path of the light beam correct yes sir that is the scattering of light from the dust particle that is present in the room that is tindal effect actually even if you have a dark room correct and you make a small small hole into the wall so that the light comes in from the outside okay you'll see the dust particle and you can clearly see the path of the light beam yes right that is also tindal effect okay so this is what they have asked so far what is tindal effect that is it one question that they may probably ask because they haven't asked yet is the condition of this tindal effect means what are the condition to be satisfied to show the tindal effect okay the first condition you write down just write on condition the first point the diameter of the dispersed particles diameter of the dispersed particles is not much smaller than the wavelength of the light used means the point is in like the short way what you can say the particle is the that right down the diameter of the dispersed particles is not much smaller than is not much smaller than the wavelength of the light used see why is scattering takes place that is only possible when the particle colloidal particles and the wavelength of the light particle size and wavelength of the light that you're using is comparable then only scattering takes place that is one condition second one is the refractive index of the dispersed phase the refractive index of the dispersed phase and dispersion medium must differ greatly in magnitude a refractive index of the dispersed phase and dispersion medium must differ greatly in magnitude done written yes so can you repeat that last point the refractive index of the dispersed phase and dispersion medium must differ greatly in magnitude sir it's not like the dispersed phase should be lesser or anything they should just differ ha that difference is not required means that if it is same then diffraction won't be there then the scattering won't be there that's why i just have a doubt i mean why won't so we're talking about scattering as in like refraction and all that right uh not exactly a reflection so why does it have to be why does why does a difference have to be there so it's just great difference have to be there that's my question see the thing is if the difference is not there okay yeah then suppose the we have two things dispersed phase dispersion medium so one will deflect the light in some different direction like scattering will be there because of that something like mesomeric compounds yeah like that only if you don't have much difference then that will nullify okay so and this condition you see the most important part here this condition is satisfied by a liophobic poloids got it liophobic color then there are high chances that they ask you which of these collides shows tindal effect liophobic or liophilic answer will be liophobic collides because in liophilic collides the difference in magnitude of refraction index is not that much it is almost to zero or very small difference is there okay so liophilic collides does not show tindal effect got it yes sir yes sir okay last two things we'll discuss the emulsion and all there's only definitions okay so i'm not doing that okay so you can go through ncrt it is given over there the definition definition of emulsion in example i'm leaving that okay because there are two more things i need to finish today because that's what i'm taking now yes okay see there is um well like i said um hardy suzerule you can apply once you know the charge on the collide okay so one thing is very important few examples i have given you when you take fecl3 this is very important you must remember fecl3 and you add excess of water into it h2o excess what you'll get you'll get feo edge whole thrice plus htn okay so this ferric oxides feoH whole thrice if water is excess water is excess then this one is actually gives this feoH whole 3 and it is surrounded by fe3 plus okay water if you are taking it is surrounded by fe3 plus and hence it is a positively charged soul this you must remember positively charged soul okay it is a positively charged soul when fecl3 with h2o we have but if you are taking fecl3 with naoH okay it again forms feoH whole thrice with nacl but this is now surrounded by oH minus oH minus in this case it is a negatively charged soul so this you must remember negatively charged soul okay with naoH and with h2o when you solve the questions also if you get some other soul which is not written here you must note it down okay because the charge you must know on the soul yes the last thing we have to discuss here is electro kinetic potential potential or we also call it as zeta potential zeta potential see if you have agi and electrolyte okay agi sorry it is a ppt we have precipitated and when you add ki and electrolyte into it then what happens this agi is surrounded by what surrounded by i minus common ion common ion correct so like this it is surrounded by the common ion agi with i minus agi with i minus and so on right so basically we have silver iodide precipitated surrounded by i minus like this i minus like this and since there is also k plus present in the solution okay so this i minus also attracts k plus towards this side possible i minus and k plus interaction okay so the first layer that you get here this layer because around this we have k plus if i write down this way this side we have k plus and k plus so this layer okay when the combination of two layers of opposite charge around a colloidal particle is called hem hose electrical double layer so this layer is electrical double layer or simply electrical double layer you can consider okay and in this the two layer are separated okay this layer the first layer that you forms here this we call it as fixed layer it is fixed and this one is diffused this layer that you form this side is diffused layer right and we always know this thing is always true when two charged particles are surrounded by right from distance there must have some potential difference correct the potential difference between the fixed layer and the diffused layer is called what zeta potential understood write down the definition between the fixed layer and diffused layer zeta potential is the potential difference between the fixed layer and diffused layer understood so just we have definition of it electro potential electro kinetic potential and zeta potential just you need to keep this in mind this is it for this chapter okay like i said ncrt you have to focus on okay they form questions from ncrt for these chapters okay so main focus on ncrt go through it completely properly okay and then for solving questions you can refer any other book i'll share the assignment also okay but we have discussed many things the important thing i'll tell you again physical chemical absorption the key point you must remember okay colloidal thing gold number how precipitation takes place charge on colloids all those things are important sir i have one doubt tell me how do we consider colloid as a surface phenomenon colloid is colloid is not a surface phenomenon then why do we start in surface chemistry no surface chemistry actually you see when colloid forms you see that it is not a surface phenomenon exactly but when you have that elect that precipitated agi and you put some electrolyte onto it then between i minus and agi there is some interaction right so when the surface when the two phases are there or at the interface what kind of interaction is there how they interact with each other that is what we are discussing so in soap what happens in soap there is again the interaction between the hydrophilic part and you know and oil and grease again two phase we have hydro sorry hydrophobic part and oil increase hydrophilic part with water okay so always you see there's the interaction between the two phase or particles we have so surface chemistry we study about when at interface or when interaction takes place what is the chemical change we have how energy change how you know the process or the system goes towards stability all these things we'll discuss over there yes sir so that's how it is and even you see in zeta potential we have interaction at the interface ions accumulate both sides so that will you know generate a potential difference that's how that's what it is zeta potential and electro kinetic potential yes sir okay so this is it we'll wind up the class here okay for next class we'll let you know when it will possible sir have we finished biomolecules or that nucleic acid we study by ourselves right nucleic acid if you want you can study i usually don't teach that okay because it's if you want i can take for half an hour it's not that big thing also we'll see next class we'll see what to do okay thank you sir yeah thank you thank you sir thank you sir no no that's because he already left but yeah what happened okay take care thank you sir