Day 3 | Chemistry 2 | EAPCET 2026 Online Classes | @srichaitanyagosala

Ajouté : 2026-05-12

[00:00:03]Good afternoon everyone.

[00:00:08]Last two days we have discussed two chapters. One is uh solid state and so and today uh we'll be discussing uh surface chemistry. Solid state and states of matter discussed already today surface chemistry means on the surface level. Okay. What are the phenomenon that we are going to see first? In that we'll see the concept of absorption.

[00:00:35]This is purely theoretical chapter.

[00:00:37]Numericals no you don't get numerical questions on that purely theoretical. So if you open NCERT there are lot of lot lot of content is there. It is difficult to manage within the few days for the preparation.

[00:00:50]uh so listen to the class I will focus on the important points what you need to remember so that you can handle the questions in exam mostly questions come in these areas only so listen carefully and uh I I also show you the important points in the NCERT in the underlined manner you can revise them later on also if you want so first we'll see absorption first understand what is the difference between absorption AB absorb Absorption and absorption. A d see suppose if I take a chalk piece and if I put this chalk piece in the ink bottle and keep it for some time and take it out. Now you will see suppose that is blue color ink bottle. You will see all the blue color on the chalk piece.

[00:01:38]If you break this chalk into two pieces inside if you look you don't see the ink blue color ink inside. Inside you will see the water. That means what? The ink the colored pigments of the ink only attached on the surface of the chalk piece but not penetrated into the bulk of the chalk piece. That means into the chalk piece. What is penetrated into the uh chalk piece inner portion of the chalk piece? Water which is a solvent in the ink bottle that is penetrated into the ink uh chalk piece. So whatever is gone into the bulk of the substance we say that is absorbed. Absorbed means it is went into the inside. What is attached on the surface of the substance that we say absorbed. So here in case of uh immersion of chalkpiece in the ink bottle scenario the colored pigments absorbed on the chalkpiece whereas water being absorbed into the chalk piece.

[00:02:42]This is the difference between absorption and absorption and today uh this chapter we are going to discuss on the surface phenomenon means absorption.

[00:02:50]We don't deal with the absorptions here absorption.

[00:02:55]Now the equivalent of molecular species at the surface rather than in the bulk rather than in the bulk means what? Not into the substance only on the surface of solid or liquid is termed as absorption. D and in this terminologies these are the terminologies we use. Uh suppose ina in the case of chalk piece on the chalk piece something has attached whatever is attached that means the colored pigments there right attached the colored pigments are called absorbate that substance is called absorbate and chalkpiece is called absorbent.

[00:03:40]This is the uh terminology which is accumulates on the surface that substance is absorbent. Uh the main substance which provides the surface that is called absorbent.

[00:03:55]Now for example these are the examples given if a gas like oxygen H2 CO etc is taken in a closed vessel and in that closed vessel you put a powdered charcoal.

[00:04:07]Powdered charcoal you keep it inside.

[00:04:10]Then after some time the pressure in the container due to the gas the pressure exhibits the pressure in the container comes down because some of the gas in the container go and attached on the surface of the charcoal material. So because of that the freely moving gas content will decrease. Therefore pressure in the container will decrease.

[00:04:33]That's what return pressure of the gas in the closed will decrease. Similarly another example in a solution of an organic dye. Organic dye. Dye means colored substance. Organic colored substance we say say methine blue.

[00:04:45]Methane blue we take let's say and there's a methane blue solution that means there's a solvent water and methine blue is mixed in that and you will see the blue color solution of this blue color. In this blue color solution we are adding animal charcoal. Animal charcoal when it you add after some time the blue color disappears and becomes colorless. Finally the solution that means what happened to this blue color the blue colored pigment that meanth blue materials which is responsible for the blue color that methyline blue particles will go and attached on the animal charcoal that's why the solution becomes colorless. So here this example deals with gas absorption on the solid.

[00:05:35]This deals with liquid absorption on the uh solid. So like that there are various examples. Air becomes dry in the presence of silica gel. If you take silica jelly something if suppose if you order some equipment uh materials in the Amazon or flip cart sometimes you see there are small packets they will send along with the mater objects you have ordered in that small packets if you open small transparent beads will be there you know what are those be beads those are the silica gel beads why they kept inside the ordered purchased objects because this silica gel L absorbs the absorbs the moisture absorbs absorbs the moisture.

[00:06:25]So and then and keeps the air dry.

[00:06:29]Otherwise what happens if moisture content is present in the air or in the air present in the packages then bacterial growth will be more that will that may cause harm to the objects. Uh so to prevent that they use the silica gel materials.

[00:06:47]like that. Next and removing. So attaching to the surface is called absorption. The opposite removing of the particles from the surface is called disorption.

[00:07:07]Absorption opposite disorption.

[00:07:11]Sometimes both absorption and absorption. Absorption. absorption both takes place simultaneously. In the case of chalk piece both took place simultaneously. So in such scenario we uh use the word absorption.

[00:07:26]Zorption means both absorption absorption together takes place. That's why we use the word in such cases absorption.

[00:07:36]And what happens in the case of absorption? Delta H will be negative.

[00:07:41]Delta S also negative. So remember when absorption takes place delta H is negative means exothermic delta S also negative.

[00:07:59]Why? Because when attractive forces are operating and bringing absorbent and absorbent together. And whenever attractive forces operate and bring the objects together potential energy decreases of the system means always it's an exothermic process. That's why we say in chemical bonding process also whenever attractive forces are operating to bring the things together energy will be released during that's why during chemical bond formation energy releases delta H is negative exothermic so delta H negative fine and what about delta S delta S is also negative because suppose a gas is there and it is absorbed on the solid What happens actually earlier the freely moving gas has more disorder but when a part of the gas is absorbed attached on the surface now it it has no longer a free motion free mobility therefore since its motion is restricted we say its randomness is less now so earlier more randomly moving gas has become less random now that means delta s becomes uh negative So both are negative remember and we know delta G is equal to what now this is negative and this portion is also negative because delta S is negative but in the beginning of absorption first part delta H is more negative that's why even if you subtract this thing the overall net value is negative only because it is more negative neative value. So delta G in the beginning is negative. So react process takes place.

[00:09:52]But after some time as process continues delta H which is more negative in the beginning as a process continues it becomes less and less and less negative and finally delta H value T delta S value will be equalized. When they equalized delta G becomes zero. That is the state we say equilibrium is attained means there is no further absorption takes place. After that there is no further change in the content.

[00:10:24]Uh till then absorption takes place.

[00:10:27]Once the delta G becomes zero we say equilibrium is established. Equilibrium between what and what equilibrium between absorbing molecules and the disorbing molecules. when molecules keep absorbing some of the molecules leave the surface. So in the beginning absorption attaching molecules are more compared to the losing molecules but after some time when equilibrium is attained suppose if n number of molecules attached per second same n number of molecules leave from the surface per second so there's an equilibrium that's what written also in the NCERT text delta s negative delta G is this as the absorption proceeds delta G becomes less H becomes less and less negative ultimately it equalizes to T delta S mean delta G becomes zero which is the equilibrium state absorption two types of absorptions uh this we have explained in class also because this part is there in the neat exam also we have explained bit physoption chemist option physoption physical absorption sorry this part is not there uh in the NET exam. Uh liophilic souls, liophobic souls part we have explained in class.

[00:11:46]Physoption chemist option is not explained in class uh because it is not there in the NET but it is there in MEC.

[00:11:53]Physoption chemoption means physical absorption chemical absorption. See if just Vanderval's forces bring the particles to the surface and attach that is physical absorption.

[00:12:08]If suppose an gas or liquid comes to the surface and attach due to the chemical bond formation between them due to the chemical bond formation they attach that is called chemical absorption. Now in this chemical absorption case more it is more exodmic because chemical bonds are forming there in physical absorption only vanderal forces bring the things together. So in case of chemical absorption where chemical bonds are formed, it is more exothermic in nature more energy will be released. First thing we will see all those points in the NCERT but listen first exothermic and secondly since chemical bonds are forming here activation energy is also more for the chem option. Physical there is no bonds so activation energy is less there. Chemical chemical option activation energy is more.

[00:13:04]Next chemical bonds cannot form between any two things only when there is a possibility it will between the materials then only bonds will form. So chemis option is highly specific.

[00:13:17]Physes option vanderval forces exist between any two substances you take.

[00:13:23]Yes. So in some between some substances the andos attractions may be more between some it may be less but they exist universally between any two substances but chemoption is highly specific.

[00:13:37]Next in case of physical absorption multi-layers will be formed. Suppose one layer is absorbed and again on the top of it another layer another layer another layer like that multiple layers will be can be formed.

[00:13:54]Just like if you take a magnet and put one nails one layer of nails and bring another layer that also you can form attractive force still operates.

[00:14:03]So like that uh physical absorption multi uh multiple layers can be formed but chemical absorption only single layer because only for the first layer only can form bonds with the absorbent material below. Once you bring the second layer, it is not in contact with the absorbent material below. So only single layer here. Now let's see the points.

[00:14:28]Weak vandrols forces operate in physical absorption. Whereas chemoption what is the what are the things present?

[00:14:34]Chemical bonds.

[00:14:40]I'll show you the uh summary of all those in the table formed. But first uh see this question. Which of the following is true for spontaneous absorption of H2 gas without dissociation on solid surface? Means when H2 gas without breaking into atoms when H2 gas is just absorbing on the solid surface. What is correct in that?

[00:15:04]When absorption is taking place when absorption is taking place delta H will be negative.

[00:15:12]Okay. So exodermic process always absorption is exo and also delta s also negative. See delta h negative delta s negative delta g also negative till equilibrium is reached. So easy to remember all negatives.

[00:15:30]So exothermic means delta is negative and delta s also negative yet positive they have given. So this is fine.

[00:15:38]This is the answer.

[00:15:41]Next let's see the differences between them in the form of table physes because of what vanderol's forces just now explained here chemical bonds here this is highly specific you cannot form bond with between any two substances you choose highly specific but here not specific and phys option is reversible in nature reversible forward motion is taking place backward motion also takes place both are taking place reversible and whereas uh this one chemoption is not a reversible process it is irreversible process this is also an important difference and it depends on the nature of gas it also depends on the nature of gas yes some gases absorb better through bonds or through vandals forces so definitely nature matters And enthalpy is low here because bonds are not forming. So energy released also will be less. But here energy released will be more. And here NCERT 80 to 240 given. But in some books those values will vary. Uh they may write about 300 400 also it don't focus much on that numbers but just remember physic.

[00:17:07]Next, low temperature is favorable and this is also another important point. If you maintain low temperature, physical absorption will be better. If you increase the temperature, then they easily leave the surface. Vander's forces can't hold them. So, they easily leave the surface molecules. So, higher the temperature, lesser the absorption, physoption, physical absorption. When it comes to chemical absorption, higher the temperature, higher the absorption, chemtion because it requires higher activation energy to form chemical bonds. So if you increase the temperature, more molecules cross the activation energy barrier and forms the chemical bonds. That's why higher the absorption, higher the temperature, higher the chemical absorption. But in physical absorption higher the temperature lesser the physical absorption. Very very important difference. And uh here no appreciable activation energy. Not a not a good activation value. But here higher activation energy involves. And uh when surface area is more it increases with surface area definitely here also when surface area is more more absorption.

[00:18:27]And here it is a multimolecular multiple layers will be formed multimolecular layers whereas here chemist option case only one layer that is these are the important differences which are the following is not a characteristic of chemoption.

[00:18:47]Absorption is highly specific. Yes specific chemical bonds can form between the uh possible substances only. Heat of absorption is see in NC it is given some around 80 to 2 240 like that but here it's different given but don't focus on those numbers three-digit number is fine we cannot some books have different values also so don't immediately judge from that decide from that go through the other options also first the process is irreversible this is also right for chemist option it forms multimolecular this is absolutely wrong only unilayer not much. So by looking at all the four options then decide if is there any absolutely incorrect one is there. If you don't find any such thing then you can select this number. So here in this case this is the incorrect.

[00:19:42]Which of the following is not correct?

[00:19:45]Again not correct also. Both physical and chemoption are exothermic. Yes absorption is always exo whether it is a physical or chemical. Physical absorption with decrease in free energy.

[00:19:58]Yes, decrease in free energy means delta G negative.

[00:20:02]Chem option occurs with increase in free energy. No, chemtoption also delta G negative only. Increase is wrong. So this is the wrong one. Physical absorption requires low activation.

[00:20:12]Fine. Chemical requires high activation.

[00:20:15]Just now we have discussed. Magnitude of chemical absorption increases and that of physical absorption decreases with rising temperature. Yes. In if you increase temperature chemistry option takes place better physes option will be decreased. So except B all are right.

[00:20:36]Next absorption is see isotherms means constant temperature. At constant temperature the graphs drawn are called isodms.

[00:20:53]So now see what and what graphs are drawn. See this is X by M. X is the mass of absorbed gas. M is the mass of the absorbent material. Absorbent material M absorbed gas is X.

[00:21:09]Now X by M of absorbed gas per unit mass of absorbent versus pressure. This is the pressure.

[00:21:20]Now if you see the graph X by M versus pressure see this graph is drawn at single temperature 195 constant 195 this graph is drawn this is one isma this is another isotherm at this temperature this is third ism so now if you look at this is is flot as pressure increases absorption increases and almost they become saturated after certain pressure they can't increase further they becomes horizontal that point you notice.

[00:21:54]Second, as temperature increases, just now we have discussed this is for physoption uh that is only the end of syllabus physical absorption. As temperature increases, physical absorption decreases. That's what we have uh just now seen. So see these are the temperature values. Higher the temperature the physoption y-axis value represents mass absorbed that will be lesser here at higher temperature. So these points you keep in mind and this is called friendly equation. This also you remember x by m is equal constant k into pressure power 1 by n. This graphs follow this equation.

[00:22:37]And if you apply log on both sides log x by m is equal log k + 1 by n into log b.

[00:22:45]So if you draw here suppose here if you draw a graph between these two this will be like y = c + mx form where slope m is 1 by n like that in a plot of log xm versus log p. Just now we have discussed log xm versus log p graph.

[00:23:14]This is yaxis. Log p is x ais. So it is like y = c + mx form where log k is the y intercept. 1 by n is the slope. Now see the question in a plot of log xm versus log p for the absorption of a gas and solid a straight line is obtained. The slope of that straight line slope is what? 1 by n is the slope. Just now we have discussed.

[00:23:44]So answer is first one.

[00:23:50]The flu absorption is varies with temperature according to the figure given below. Choose the correct option.

[00:23:57]See and we know that as temperature increases absorption comes down. So T4 must be the high temperature.

[00:24:06]This must be the highest. This must be the lowest. So among the options where is the T4 highest and T1 lowest? This is the one. So third option is correct.

[00:24:19]Like this you have to decide.

[00:24:27]Next in the surface chemistry chapter next is about the cat catalyst and um see you know catalyst decrease the activation energy and increase the speed of reaction but some substances increase the activity of catalyst they are called promoters promote the catalyst. Some substances decrease the activity of catalyst they are called poisons.

[00:24:53]So promoters means increase the activity of catalyst they will decrease. Suppose in hab's process if you take in hab's process this iron is the catalyst you know iron is the catalyst in hab's process and uh malibdinum is also used in that process.

[00:25:13]You know why malibdinum increases the activity of the iron catalyst.

[00:25:18]Iron catalyst activity will be increased. So malibdinum in this example we can call promoter catalytic promoter like that. Next homogeneous and heterogeneous catalysis.

[00:25:33]If catalyst and reactants are in same phase we call it homogeneous catalysis.

[00:25:40]If catalyst is in different phase from the reactants that is heterogeneous catalysis. For example, see here reactants are gases, catalyst is also gas.

[00:25:54]And here reactants are liquids, catalyst is also liquid. Therefore, homogeneous examples. These are aquas also means liquid only. Liquid state, liquid state, liquid again homogeneous. Heterogenous gas and solid different. So that is heterogenous. So how you will get questions on this direct which of the following is an example of heterogeneous catalysis. So look for the different phases here all are gases homogeneous hydrarolysis of aquas in the presence of aquas liquid liquid again homogeneous clearly visible one is liquid here reactant whereas catalyst is solid different so this is heterogenous. So like that you identify next enzyme catalysis. You know in biomolelecules chapter also you have seen enzymes are bio catalyst. Uh they increase the speed of reaction by reducing the activation energy. Now some important enzymes you must remember. In the next page it is summarized in the form of table. First see here invert is inverted you know cane sugar cane sugar hydraysis is called inversion of sucrose. So from that you can easily remember the enzyme name invertise and zyase glucose converts into ethyl alcohol and CO2 due to zyase and diastas is an enzyme act as catalyst to convert starch into malttos or in other words hydraysis of starch will give the maltos when we use dastage enzyme and after that again from the names you can tell easily maltos hydraysis to gluc Glucose is called maltis and ura conversion to ammonia uria hydraysis into ammonia and CO2 is catalyzed by uras and in stomach you know in stomach pepsin enzyme converts proteins into peptides and finally that peptides also break down into amino acids which is not given in here but and in intestine the trin from pancreas the trin enzyme converts converts proteins into aminosis. So in stomach pepsin and in intestines tryin these two both nature is same only they convert proteins into first peptides and then amino acids and you know milk into curd lactobacilli enzyme present in curd.

[00:28:48]Next These are all summarized here whatever is written in the above page. So which enzyme catalyzes what reaction and uh these are the other points related to enzyme. Enzymes there one enzyme catalyzes millions of reactants because catalyst participates and at the end comes comes back again and again can catalyze another reaction. Like that one enzyme can catalyze millions of reactant molecules. So small portion is sufficient for that. Next one catalyst cannot catalyst more than one reaction. So suppose zysey you take it is for only for glucose. Part if you take it is for malttos. It won't work for other reactions. So it is only it is enzymes are very specific in their reactions.

[00:29:44]Next optimum temperature. If temperature is too low also they fail to work properly. If temperature is too high also. So optimum temperature range is this. Optimum pH also too low pH fails high pH also fails. 5 to 7 is optimum.

[00:30:05]Next a collide is a heterogenous system in which one substance is dispersed and next next we will see the collides.

[00:30:12]Topic of collides. uh this part we have discussed in the regular classes for need syllabus a little bit at that time I explained we explained that there are three types of solutions true solution collidal solution suspension so they differ only in the size range of the solute particles if solute particle size is 1 to 1000 nanometers uh then we call that collidal solution that collidal is only there in our syllabus in surface chemistry we discussed So collide is a heterogenous system not uniformly distributed solute particles in which one substance is dispersed phase and another substance is dispersal.

[00:30:57]Say suppose if you take glucose in water we know glucose is solute water is solvent simple but in case of collides the same terms we use it differently there solvent the term solvent is replaced with dispersion medium in collides and solute is replaced with dispersed phase. So dispersed phase means solute only. Dispersion medium means solvent.

[00:31:32]One second.

[00:31:57]Okay. So, dispersed phase means solute, dispersion medium means solvent. Keep this in mind.

[00:32:06]And what is the uh size range of the solute particles means dispersed phase particles. What is the size range? So that we can call that solution collidal solution 1 to,000 nanometers.

[00:32:20]You know how to convert nanometers into meters in case if they give in meters.

[00:32:25]Next this is one table at least whatever colors colorized things are there at least you remember them at least although the whole table is important. So here suppose dispersed phase is solid means solid solute is present in liquid solvent. Solid solute in liquid solvent.

[00:32:49]Then what is it called? The such collidal solution is called sooul not soul.

[00:32:57]Solid. So solid solute in the liquid solvent and also gel. Next immediately remember gel. You know you must have been using toothpaste or in many forms of gels you must be using already. So gel is actually a liquid solute in the solid solvent. Liquid in solid this is solid in liquid. Liquid in solid. So both are quite opposite. One is called sole other is called gel.

[00:33:25]Now when we call the collide aerosol when solid is solid solute is present in gas solid solute is present in gas for example smoke black smoke we see now they're actually the solid particles black particles is present in the air gas so smoke is a kind of aerosol dust also aerosol Now next important one liquid and liquid milk. Milk is one important example uh where liquid fat is present in liquid water. Liquid fat is a solute. Liquid water is a solvent and such thing for example milk is called what? Emulsion.

[00:34:14]This type of collide name is what?

[00:34:16]Emulsion. So whatever color colorized things are there I'm explaining liquid in gas liquid and gas also solid in gas or liquid in gas. If gas is the solvent the name is same a resolve. Next gas in liquid.

[00:34:33]Gas is present in the liquid that is foam. You must have seen foam. Soap foams foams you must have seen that is actually what? Gas is the solute present in the liquid.

[00:34:46]So liquid solvent. So these are the different types of different types of collides.

[00:34:57]Next. See this is how you will get questions. Solid in liquid. Solid in liquid. Just in the beginning only we have discussed solid in liquid is what?

[00:35:07]So liquid in solid is called what?

[00:35:13]Gel. See this is so liquid in solid gel.

[00:35:18]Okay. Uh so liquid in solid is also there. the liquid and solid. So this must be gel.

[00:35:26]Then liquid in liquid milk example liquid in liquid is imulsion.

[00:35:33]Gas in liquid is called foam. Like this questions can be asked.

[00:35:42]Next All right. Next.

[00:36:17]Souls. One. Rest of the topic is about souls. That means solid solute in liquid solvent. That is only there in rest of the chapter. In this sole solid and liquid type collides there are two types again leophilic sole liophobic. This part I have we have explained regular classes. Leophilic means solvent liking uh collidal particles.

[00:36:41]Solvent hating collidal particles are called liophobic. Phobia means hating.

[00:36:48]Phobia means fear. Uh that kind. So here it it is meaning of solvent repelling or solvent hating is what liophobic and solvent liking or loving is called leopilic.

[00:37:04]Leophilic example biomolecular things for biomolelecular polymers example starch gelatin gum rubber all these are biop-olymers. Biopolymers comes under the liophilic case and liophobic see the example liophobic are metals metallic sulfides metals are liophobic liquid heating and here liophilic soles are more stable just add the solute and solvent since they like the solvent easily mix and solvent uh collidal solution is prepared. Now uh it is very stable. So uh you have we have to struggle a lot struggle a little bit more to separate them. But once you separate and mix them back again they easily form. So they are called reversible souls. We can separate and mix again to get back them. But liophobic are irreversible souls because first of all they don't like each other.

[00:38:02]Uh collidal particle and the solvent they hate. So they don't mix easily. So we have to re rely on a special procedures methods to prepare them to mix them. And after mixing uh if if you uh want to separate them there are many ways you can heat them or you can add some electrolyte. There are many ways to easily separate them. But once they separated collidal particles and the solvent again you cannot easily form them by mixing. Again you have to rely on the special methods only. So since liophobic souls after separating them they can't easily mix and we have to rely on special procedures. We call them as irreversible souls.

[00:38:54]So liophilic are reversible souls. We can create them easily.

[00:38:59]Leophobic are irreversible souls. After separating them we cannot create them easily by mixing.

[00:39:07]That's what written here. Next another classification collidal collides are further classified in this manner based on the type of particles.

[00:39:19]See if multi first one is multimolecular collides means many molecules come together and join uh and join and when they join uh the diameter of the particle size of the particle will increase. If that size falls in the range of 1 to,000 nanometers when molecules come and combine and gives rise to the size of the particle this multimolecular particle within the size of 1 to,000 nanometers.

[00:39:52]So then we call that as collidal solution. Which type of collidal?

[00:39:56]Multimolecular collide. Second one is macroolecular collides. Here sing single molecule only macro very big in size so that its size range falls in 1 to,000 nanometers single molecule generally polymers has very big molecule each polymer chain has very big structure. So that polymeric suppose imagine a polymer is wounded on itself and the size of the particle is so high that 1 to,000 nanometers we call it as macroolecular collides multimolecular macroolelecular see in macroolelecular all are polymeric only starch cellulose proteins whether it is a man-made polymer or natural polymers comes under these examples associated associated collides Means if you take the soap molecules for example this is a soap molecule very big molecule this soap molecule has one is polar head is there polar charge is there here other side no polarity no charge so we call it hydrophilic this tail is called hydrophobic tail why we call hydrophilic and hydrophobic this likes water. This does not like that's why. Now when these molecules of soap are present in water, what happens? All these molecules come together and they form this kind of shape structure. We see hydrophobic tails since they like each other. So they hydrophobic all are facing each other interacting. Hydrophilic heads will be interacting with the water. This hydrophilic heads interacts with the water. Imagine a ball. Okay.

[00:41:53]Inside the ball molecules are hydrophobic tails are facing. Outside on the surface hydroilic heads are there in the molecules. They like the water that's why they interact with the water on the outside. So this kind of structure shape particle shape when the size falls on the falls into 1 to,000 nanometers this is called a collidal particle. This is called associated collide. So I mean hydrophilic hydrophobic tails kind of particles when they come together and form this kind of structure we call them as associated colloidal particles.

[00:42:34]Soaps, detergents, they form something like this and oil or grease materials are trapped inside this and uh and they get removed by these particles and these particles are called misles.

[00:42:48]Associated collides are also called missileles.

[00:42:54]So this misile or mi.

[00:43:01]So this uh missile is trap the oil or grease materials uh with the inside portions and they take from the cloths.

[00:43:15]Next an example for hydrophobic soil among the following. Just now we discussed all biopolymers comes under the hydrophilic liophilic liophobic means metals and metallic sulfides. So if you see these are the biop-olymers the underlined ones.

[00:43:36]So they are liophilic metal sulfide is the liophob liophobic means hydrophobic disposal phase means solute medium called solvent.

[00:43:53]Nature of collidal solution liophilic or liophobic.

[00:43:58]See gold soul s sole whenever they say so soul immediately we can tell sole term is used for solid solute in liquid solvent. So solid and liquid where is that solid and liquid combination? Yes.

[00:44:12]Now this much we can figure out from the word soul. Now whether it is a liopilic or liophobic that depends on this one.

[00:44:21]This is gold metal.

[00:44:24]Just now we have discussed metals metallic sulfides they come under the leopobic biop-olymers come under the leopilic. So metal is given gold so leopobic. So this must be the answer.

[00:44:46]Next.

[00:44:50]These are the different uh properties of collidal solutions. One is tindal effect. Tindal effect means uh in movie theaters you must have seen when light falls uh when if if you uh raise your head you will see from projector room the light path you will see up to the uh screen and you see the dust particles also moving in that uh path of the light. So this uh is called tendal effect.

[00:45:20]The path of the light is seen by you because the dust particles in the air scatter the light. That's why you see that path. So the scattering of the light by the particles is uh is called the tendal effect. Now collidal particles can do that. So collidal solutions show the tendal effect. Next uh collidal particles scatter light in all directions in space. This scattering of light eliminates the path of the beam in the collidal. That means you will see the if you put the light in front of the collal solution torch light if you put you will see the path of the light in the collal solution because the collateral particles scatter the light that's why tindal effect and uh what are the conditions for tindal effect given diameter uh should not be much smaller than the wavelength just go through it next brownian motion brownian motion means what the uh random random movement of the particles. Collidal particles move randomly and the solvent molecules dispersion media molecules come and collide them. They move. Suppose if molecule solvent molecule come and collide solid particles move like this.

[00:46:42]If another molecule come and collide, it will move like this. So like this these colladal particles keep moving randomly due to the collisions from the solvent molecules. This is called Brownian motion because the first time the scientist Brown identified this that's why Brownian motions and uh the Brownian motion depends on the size of the particles. If size is small then the viscosity friction viscosity will be less. So molecules move freely move randomly. If molecular size is big then uh its motion will be random motion will be less brownian motion will be less.

[00:47:26]That's what is said. Lesser the viscosity means smaller the size lesser the viscosity means lesser the friction between solvent and the solute particles. So mo motion will be faster and collidal particles always carry an electrical charge. They always carry whether they carry plus or minus that's a different story but they always carry a charge and this charge is responsible for keeping the collidal solution stable because if this collidal particles have positive charges then the two collidal particles come closer because of the same like charges they ripple and move away. If there would have been no charge, if there would have been no charge, then what happens? When the particles come closer, they attach. When they attach, the size and mass will increase like this. If couple of times molecules, particles come closer and attach their size becomes larger and larger. Due to the gravity, they start coming down. So after some time all these collidal particles settle at the bottom means we say collidal solution is destroyed we say. So for the stability of the collidal solution uh this charges on them part on the particles will help.

[00:48:46]So charges is one of the reason for the stability of the collidal particles always carry charge and which charges depending upon their methods of preparation uh these things get the positive charges these things get the negative charges. So hydrated metallic oxides these are the hydrated metallic oxides.

[00:49:11]Sometimes you will see hydroxides also oxides and hydroxides they come under this category positive basic duffs example methane blue methine blue al methine blue comes under the positive hemoglobin all these comes under the positive souls. Next, negative charged souls. Negatively charged souls they contain. What are the important examples? One is metals and metallic sulfides. Leophobic souls. Do you remember that? Leophobic souls come under this metals metallic sulfides and acidic D stuff basic basic D positive acidic D and negative. And so of all the biop-olymers, liophilic souls also starch, gum, gelatin, all this comes under this category.

[00:50:11]Presence of equal and similar charges collateral particles are responsible for providing stability. Just now I have discussed that point how charges responsible for stability. We have given that And see the process of settling of collidal particles is called coagulation. Now see if colloidal particles uh if uh they come together and slowly they come out of solution this is called coagulation or precipitation.

[00:50:47]uh uh this coagulation or precipitation means the process of settling of collidal particles is called settling is coming out of the solution settling is called coagulation or precipitation and it can be done multiple ways. One is electrophorosis. Electrophorosis means just you conduct electrolysis on the collidal solution. If colonizer particles have positive charge they travel towards the cathode. If they have negative charge they migrate towards anode and settle there. So they come out of solution uh and they just deposit on that electron material surface of the electron materials they don't attach. So this is one coagulation method. Second mixing of two oppositely charged souls.

[00:51:39]Two oppositely charged souls. If you one is positive sole other is negative sole.

[00:51:43]When you mix them both neutralize each other once they they lose their charges we know particles easily coils and increase their mass and come down of solution due to gravity. So this is the second method boiling. If you boil third method, if you boil the solutions, then molecular speed will increase and they collide more uh high in number because of more collisions. Uh when the collision happens, then what happens? A rupture happens when the molecules the particles collide that collision what happens?

[00:52:22]They lose their charged layers. Whatever the layer of charge present on them because of the collision and the rupture caused due to it uh the they lose their charges and ultimately uh they combine because of no charges they can easily combine them and come down as precipitate.

[00:52:44]Next by addition of electrolytes. If you suppose collide a solution has positive charge. If you add electrolyte means ionic compound which contains a greater negative charge on the ion. Then this negative ions go and neutralize the charges and uh what happens when the electrolyte what you have added neutralize the charges on the collides. Once they become neutral they can easily precipitate neutralization lead to coagulation.

[00:53:19]Now here one point you remember in this neutralization point only see we are adding a electrolyte which neutralize the collidal charges and bring down as bring down the uh uh these collidal particles as precipitates in that hardy skull's rule which says higher greater the valency of fauculating ion fauculating ion means the ion responsible for the neutraliz izing the colladal charge and causing them to precipitate. That ion is called fauculating or coagulating ion that helps in coagulating the colladal particles. Higher the valency of that fauculating ion greater is the power to cause precipitation. What does it mean?

[00:54:09]For example, if I have collider solution has a negative particles. Collad particles are negatively charged. Now to precipitate them we have added some electrolyte.

[00:54:23]Three people have added some some moles of electrolyte. One first person added NaCCl. One mole of NaCCl. Second person added one mole of BC2. Third person added one mole of Al3. All three persons added electrolyte. They have chosen different NCl BC2 and Al3. But they have added. Then what happens if you add NaCCl in it splits in the solution first as Na plus Cl minus. Now in that Na plus ion go and attaches on the Na plus ion go and neutralize these particles. Na plus ion go and take out the negative charge from the collidal particles and they become neutral.

[00:55:11]Okay. And Al Cl3 when you add Al +3 ions because they have negative charges positive ion only can neutralize them.

[00:55:20]So Al +3 go and take out the negative charge from that and they get neutralized and then they can combine and cos and precipitate or coagulate.

[00:55:31]Now the question is which electrolyte is better includes one aluminium ion one aluminium ion can precipitate three can neutralize three negative charges one b to one berium ion can neutralize only two one na plus one so three units of negative charges 1 al plus 3 can take care but Na plus can take care one unit of negative charges in neutralization.

[00:56:06]So hard disk rule says higher the charge Al + 3 higher Na plus smaller higher the valency or charge of the fauculating ion higher will be the greater will be the coagulation or precipitation that is what the greater is the power to cause precipitation that's why L + 3 higher VA plus it suppose if our collidal soul is positively charged then whatever electrolyte you add the negative ion in that will go and neutralize them.

[00:56:38]So there also again rule is same higher the uh valency charge if negative ion is the fauculating ion higher the charge higher it is its power to coagulate. So just keep this in mind which of the following is the most effective in causing coagulation of feric hydroxide. Now see such kind of questions how to answer hydroxides oxides these are the the hydroxides and oxides come under the uh positive souls metals metals sulfides they come under the negative souls in the table form we have discussed that positive negative souls so oxides and hydroxides positive now positive sole is there here this positive soul which are the following is the most effective in causing coagulation of feric hydroxide. So since this is positive soul we know from the table we need negative ions to coagulate them to to neutralize them and thereby causing the coagulation. Now there are here negative ion CL minus here NO3 minus here SO4 minus2 here Fe CN6 - 3 these are the negative ions positive we don't bother here negative only can neutralize the positive sole we have taken so now which negative ion is better that is the question here most effective so we know according to hard disk's rule higher the charge or higher the valency better the ability. So answer is fourth option.

[00:58:20]Similar question you see which of the following is most effective in causing the coagulation of arsenic sulfide. See metals and metal sulfides both come under the which category negative souls.

[00:58:31]So this is a negative soul. Now this time we have to look for the positive ion which neutralize them. Here positive is K plus. Here positive is Al + 3.

[00:58:44]Mg + 2 K plus. How many are there? It does not matter. What is the ion? So K plus. Now so see which of them has higher higher valency or higher charge. Aluminium plus three. Therefore this is most effective.

[00:59:04]This is how we have to uh decide.

[00:59:08]That's it. So whatever points I have discussed first beginning absorption then what is the difference between physical absorption chemical absorption then is we have seen after that catalysis then different types of collides based on the solid and liquid dispersed phase and dispersion medium. Then we have seen souls sole category of collides divided into liophilic and liophobic.

[00:59:39]After that we have seen properties of this souls and then how to coagulate and precipitate them. Just whatever points I have discussed now just go through it once again. This is sufficient. Most of the questions you can answer without reading the entire text of NCERTT.

[00:59:58]But I mean if read if you can read NCERTT line by line it will be very good because uh they may ask question at any uh section also but since time is very less if you focus on most important areas where we frequently get questions that will be better. The rest of the time you can spend on the other known topics revising them better. Instead of reading the new topic, you can spend your valuable time on the other topics.

[01:00:23]Here just focus on the points what I have uh touched upon that is that is mostly sufficient.

[01:00:31]Okay. Thank you.