 Okay, so we had discussed this at 25 degrees Celsius, kW value is this at 80 degrees Celsius, kW value is 10 to the power minus 30. Okay, kW since it is a function of equilibrium constant, okay, so it also depends upon temperature. As temperature increases, kW increases, decreases, kW decreases because this dissociation is endothermic in nature dissociation of water, okay. Now you see, we have this relation, what is this? We have kW equals to, we have kW equals to concentration of H plus into concentration of OH minus, okay. Depending upon the concentration of H plus and OH minus, we can say the solution is either neutral or acidic or basic, okay. For example, you see, for neutral solution, what is the condition for neutral solution? The concentration of H plus should be equals to what? The concentration of OH minus. Now at 25 degrees Celsius, if I write down the concentration of H plus into the concentration of OH minus equals to 10 to the power minus 14, both are equal. So we can write the concentration of H plus square equals 10 to the power minus 14. So concentration of H plus is what? 10 to the power minus 7, understood this and it out, okay. So H plus concentration is this and hence OH minus concentration is what? It is 10 to the power minus 7 only. So pH is equals to what? pH is equals to minus log of H plus concentration. H plus concentration is 10 to the power minus 7, so pH equals to minus log of 10 to the power minus 7 and hence pH is what? Whenever we say pH equals to 7, right. So this 7 pH that we have, it is at what? It is at 25 degrees Celsius, which is understood, right. So it's not like the neutral solution will have pH value always at 7, right. It can be more or less depending upon what temperature you are taking here, understood? Right. If you take 80 degrees Celsius, then H plus concentration would be what? 10 to the power minus 6.5. Is it? We have 13 over here, no? You need to solve this, you'll get H plus concentration and accordingly you'll find out pH over there. 10 to the power minus 13, so root over of 10 to the power minus 13 you need to solve and then you will get H plus and OH minus concentration. So whenever we say pH for neutral solution is what? It's 7. It is understood, we are talking about, we are talking at 25 degrees Celsius, right. It's not like we always have pH 7 for neutral solution. We have to take care of temperature condition in that case, okay. This is one thing. Now if you talk about acidic solution, so what is the condition of acidic solution? If the solution is acidic, then we can have this condition that the concentration of H plus should be more than the concentration of OH minus, yeah. And hence we can say the concentration of H plus should be more than 10 to the power minus 7. If I take minus log both side, so minus log of H plus, less than minus log of 10 to the power minus 7, minus log of H plus is pH less than 7. This is the condition of acidic solution that you have done in 9, 10, 10 grade that for acidic solution pH is less than 7. Mathematical definition, derivation is this. If pH is 7, then POH is what? Gradle and 7. See like pH, you can explain POH also. POH is equals to minus log of OH minus concentration. Now you see for basic solution what we have. This is the condition we have. It means the OH minus concentration or if I take in terms of H plus, it should be H plus concentration is less than 10 to the power minus 7. If you take minus of log both side, pH is greater than 7 and POH is less than 7 for basic solution. Copy this down. So these are the three conditions we have for neutral for acidic for basic. What is the value of pH and POH? Okay. Again, you see one more thing here at 25 degree Celsius, we have KW equals to 10 to the power minus 14. So PKW if you calculate here, that would be 14 here minus log of KW. All the definitions are same. If you write on pH, POH, PKA, PKB for acid and base, we have similar formula for that. Okay. So we have this expression H plus concentration into OH minus concentration equals to 14, sorry, 10 to the power minus 14. If you take minus of log both side, minus of log 10 to the power minus 14, we can also expand this by log formula log of H plus minus log of OH minus and this side we have 14 minus log of H plus is pH minus log of OH minus is POH is equals to 14. So what we can write at a given temperature, if pH increases, then POH decreases and vice versa because the PKW value is fixed. Yeah. Okay. Now tell me one thing here. You know that association of water is endothermic, I'll write down this information here of water is endothermic, right? Okay. Now the question is what happens if you increase the temperature means what happens to pH, what happens to POH, if you decrease the temperature, same thing, what happens to pH and what happens to POH. Could you think? First, you just tell me the answer for the first one, but temperature increases and what happens pH increases, decreases what? Both decreases, yeah. So we know the reaction is endothermic and once you increase the temperature, the reaction will go in forward direction. So we have this reaction you see H2O, H plus and OH minus, tell me when the reaction goes in forward direction, the concentration of H plus increases or decreases, the concentration of H plus will increase and OH minus also increases, right? So this, when the concentration of H plus increases, pH will decrease because we have this, you know, relation, concentration of H plus inversely proportional to pH, right? And concentration of OH minus inversely proportional to POH, yeah. So both H plus and OH minus concentration is increasing, so pH will decrease and POH will also decrease. When temperature decreases, the reaction goes in backward direction, right? So pH and POH both increases concentration. Why can't we say this here, that if pH decreases, because the sum is pH plus POH equals to 14, if pH decreases then POH should increase, is it possible? Tell me, can we say that since pH decreases, POH should increase, isn't it? Yeah. So answer for this question is that here the temperature is not constant, right? KW will also decrease as you change the temperature, the value of KW is fixed at a particular temperature, right? So this is the relation we have at 25 degrees Celsius. The same relation will hold true for this one, pH plus POH equals to 13 at 80 degrees Celsius. You see the KW also decreases here, right? Since we cannot do by this way, right? If this increases, this decreases, because we are changing the temperature itself, that leads to change in KW also, correct? So this is true as temperature increases, both pH and POH decreases, as temperature decreases, pH and POH increases, okay? Okay. We have one more relation here for acidity. Write down the heading all of you, acidity. Acidity is what? It is the tendency to give, tendency to release H plus ion in the solution. More H plus, more will be the acidic, more acidic the compound will be, right? More H plus it gives, more acidic the compound it will be. Suppose we have a compound, we have an acid HA and when this releases H plus, we get A minus over here and H plus, right? So if you talk about the value of KA, the equilibrium constant for this reaction, A stands for acid. Equilibrium constant for this reaction for an acid, it is concentration of H plus, concentration of A minus divided by HA, this is the relation we have, okay? KA is what? KA is the dissociation constant, constant for acid or we also call it as ionization constant for acid. So you see what happens if KA increases, again we have one condition, if KA increases you can understand this KA as the equilibrium constant of an acid. So once this KA increases, we'll have forward reaction, forward reaction means the concentration of H plus increases, right? Concentration of H plus increases means what? PH decreases, concentration of H plus increases means PH decreases and acidity also increases. More H plus you give, more acidic the compound will be, right? Hence the relation overall what we can write? Overall we can write, overall we can write acidity is directly proportional to KA value because more KA, more H plus, more acidity, KA value and inversely proportional to PKA value. Is this fine? Yeah? KA and PKA are inversely proportional, how do you define PKA? PKA is equals to, like we did PH minus log of KA, exactly same definition we have. You must remember we have done GOC and in GOC we calculate acidity and viscosity. So sometimes they also ask you the order of KA, the order of PKA, they won't ask you this acidity they won't write, they will write order of, what is the order of KA for this compound? What is the order of PKA? So for all these kinds of questions you need to first find out acidity only and then you can arrange accordingly, okay? Then next you see basicity, basicity is the tendency to produce OH minus ion, tendency to produce OH minus ion, more OH minus ion, more will be the basicity, okay? Suppose we have a base and that is BOH, this gives B plus OH minus and for base we will write on KB, B plus OH minus BOH, KB is the same thing for base, dissociation constant for base or ionization constant for base. Again we can write on the same relation here, KB is the same thing for base, dissociation constant for base or ionization constant for base. We can write on the same relation here, if KB increases, forward reaction again, concentration of OH minus will increase, when concentration of OH minus increases, basicity increases but POH decreases, so overall what we can write, overall we can write basicity is inversely proportional to POH, sorry, inversely proportional to PKB I should write, PKB and directly proportional to KB, okay? All these relation they can ask you anything, PKB, KB anything they can ask you, okay? Now another term we have conjugate acid base pair, have you heard this name? Conjugate acid base pair, little bit you remember we have discussed this in GOC, right? Conjugate base conjugate acid isn't it, right? So all of you guys start revising GOC, that's why I have kept this in your chemon, next chemon because after this chapter we will be starting organic, so you must have the revision of GOC that we have done already, okay, must revise that, okay? So conjugate acid base pair, what is conjugate acid or conjugate base? Conjugate base, how do we get? Because you have an acid HA, right? And from this HA if you remove H+, you'll get A-, so this A- is the conjugate base, conjugate base of this acid, means any acid if you want to, you know, write down the conjugate base of that acid, remove H+, from there, simply, for example you see, HCl, what is the conjugate base of HCl? Conjugate base of HCl, Cl-, yes, what is the conjugate base of HNO3? Conjugate base of HNO3, tell me, NO3-, what is the conjugate base of HF, conjugate base of HF, F-, conjugate base of, conjugate base of, we can write H2SO4, what is the conjugate base of this? H2SO4, remove one H+, you'll be having HSO4-, conjugate base of HSO4- is SO42-, so simply you need to remove H+, from an acid, you'll get the conjugate base of that particular acid, okay? Suppose you need to find out the conjugate acid, so this is the, this is suppose the conjugate base we have, next is conjugate acid suppose, just opposite of it, conjugate acid you need to add H+, on the compound, right? For example, if we have NH3, this is the base, so the conjugate acid of this base is add H+, on this, NH4+, is the conjugate acid of this base, suppose we have HCO3-, conjugate acid is what? Add H+, H2CO3, suppose we have HSO4-, conjugate acid would be H2SO4, suppose we have OH-, conjugate acid would be H2O4, so like this we can find out the conjugate acid of a base or conjugate base of an acid, is it clear? Yeah, done? Okay. So in a reaction, you can identify on this basis that which is the conjugate acid base pair, for example, suppose if I write out at Cl+, NH3 gives NH4+, plus Cl-, could you tell me the conjugate acid base pair over here? What is the conjugate acid base pair here? So NH3 is the base and NH4+, is the conjugate acid of this base, so this one is the conjugate acid base pair, right? HCl is the acid and Cl- is the conjugate base of this acid, right? So this one is conjugate acid base pair, so you need to identify this, which is the conjugate acid base pair here, because based on this, we are going to understand a concept here and that concept is leveling effect, okay? So before that, one order just to write down the heading here, that is the relative strength of acids, relative strength of acids. This order just to copy this down, HClO4, HI, HBR, H2SO4, HCl, HClO3, HNO3, H3O+, H2C204, H2SO3, HSO4-, HClO2, H3PO4, HF, H2CO3, HC204-, CH3COOH, we have H2S, HClO, NH4+, HCN, H2O2, H2O, NH3OH-, done? Yes, guys, finished? Tell me, okay. So you don't have to memorize this, okay? The best part of this is what? You don't have to memorize the entire series, but at least the first line you should keep in mind. And all these, you know, acids are basically strong acid you can keep in mind easily, stronger than S3+, that is what you need to keep in mind, okay? Now, based on this, we are going to understand one concept and that concept is called the leveling effect, right down the heading, the leveling effect, okay? What is the leveling effect you see? First of all, we define this concept with respect to one particular solvent, okay? Suppose water you are taking or you are taking ammonia, any solvent, but with respect to the solvent, we have this. Let me just write down a few reactions you will understand with this, you know, examples. We have, suppose, HClO4 plus H2O, this gives H3O plus CLO4-, okay? One more reaction you see, HNO3 plus H2O gives, again, the conjugate acid of this H2O which is H3O plus, plus NO3 minus, HF plus H2O gives H3O plus, plus F minus. Now we will see this three reaction over here. Okay. So, HClO4 is the acid, right? In fact, it is a strong acid. It is a strong acid. This is also a strong acid. This one is not that strong, HF. HF is a weak acid. It's not that strong. So, actually, what happens, you have, suppose, a solution, water is present over here. So, here, suppose, we have H2O, water and HClO4 acid you have put in. So, actually, what happens, both water and acid that you are putting, and listen to me very carefully here, both water and HClO4, they have the tendency to release H plus iron in the solution like this. I'm just taking an example of this acid that is HClO4. They have the tendency to release H plus in the iron. So, both compete with each other. To furnish H plus iron in the solution, both will compete to each other. The one which is more powerful, that will release H plus iron in the solution. And most of the H plus iron present in the solution is because of the stronger one. So, which one is stronger? Which one is stronger? HClO4 or H2O? Obviously, HClO4. So, here, what we say, once you put HClO4 in water, the H plus that you get here, it is mainly because of HClO4, not because of this water. So, what happens in this reaction? HClO4 will release H plus, H2O will take H plus, forms H3O plus and CLO4 minus. Yeah, I said what? That we have H2O and HClO4 both have tendency to release H plus iron in the solution. So, the one which is more powerful, that will release H plus iron because both are competing with each other. It's like H2O is not that powerful. It cannot dominate HClO4. But HClO4 can. So, HClO4 dominates this thing, H2O and HClO4 is the acid which furnish H plus iron into the solution mainly. And we say most of the H plus iron which is present in the solution, it is because of HClO4, it is not because of H2O. Is it clear? Yes, tell me. So, HClO4 will release H plus and H2O will take H plus. So, this is an acid. This is behaving as a base, forms H3O plus and this. So, here you see if you can understand here, it is a base. And this is the conjugate acid of this base. And this is the conjugate base of this acid. Any doubt in this? Similarly, HNO3 is also a strong acid. So, same logic we have here also. And if you look at that series, if you look at that series, HClO4 is stronger than H3O plus, isn't it? Look at that series and tell me. HClO4 is stronger than H3O plus? Yes or no? Tell me guys first. Is it? HClO4 is stronger? Even it is the strongest one? So, hence, from strong acid to weak acid, it can go. The reaction can go. Hence, this reaction goes in forward direction. Look at the reaction. It has tendency to go in forward direction because it is forming weak acid. Similarly, HNO3 is also stronger than H3O plus. This reaction also goes in forward direction. This reaction, if you think of, it is a weak acid, right? And if you look at the strength of H3O plus, H3O plus is stronger than HF. Look at the series and tell me, is it? H3O plus is stronger than HF, right? Hence, this reaction won't go in forward direction because a weak acid cannot form a stronger acid than itself in any reaction, right? So, on the product side, we always have weaker acid than the acid which is there on the reactant side, okay? So, this reaction is in backward direction. So, this is one information or you can have with that series on the basis of the strength of strong acid or the acid which is there on the reactant side and the conjugate acid on the product side by comparing the strength of them. That is one thing. Now, another thing is what? You see, what happens here? Once you dissolve HClO4 in water, what acid you are getting? Could you answer? Once you dissolve HClO4 in water, what new acid you are getting? Yes, tell me. This reaction takes place between HClO4 in water and we get a new acid that is H3O plus. Yes, these two reacts and in the reaction, we don't have HClO4 present. It converts into H3O plus, correct? Yes, guys, all of you, tell me. It converts into H3O plus, yes? Yeah. Similarly, we have HNO3 also. It converts into H3O plus. So, what is actually happening in the reaction? If you look at this, we have dissolved two different acids in water, but both converts into one common acid that is H3O plus. Yes. So, the strength of H3O plus, whether you get it from HNO3 or from HClO4, the strength of H3O plus is same, will be equal. Hence, we say what? That these two acids in aqua solution, their strength becomes equal and that strength becomes equal to the strength of a new acid that forms, which is H3O plus, right? So, this is what these two acids of different acidic strength comes back, comes to this equal strength of H3O plus. This we call it as the leveling effect because two different strength of an acid comes at the same level of acidic strength once it dissolved in water. This we call it as the leveling effect of water. Two different acids, their strength become equal in aqua solution and that is equals to H3O plus. This is called the leveling effect of water. Did you understand this? Clear? So, if you look at this series, the relative strength that I have given you, in this series, you take HClO4, you take HI, HBr, H2SO4, HCl, till HNO3, till here. Whatever acid you take, you dissolve in water. Finally, what you will get? Finally, what you will get? When from HClO4 to HNO3, you dissolve in water. Finally, these acids converts into what? Converts into H3O plus? It releases H plus ion. Water will take H plus from these acids and converts into H3O plus. Yes. Right. So, what we say, the strength of all these acids from HClO4 to HNO3, the strength of all these acids becomes equal in water and that is equals to the strength of H3O plus. Since the strength becomes equal, it comes at the same level. It is the leveling effect of the solvent that we are using, which is water. It is the leveling effect of water. Tell me, is it clear to all of you? Could you respond? You know, we have three different batches. I'll tell you one thing. One is Kormangla 11th, right? Another one is yours batch, Rajinagar. And another one is YPR. And one more, we have HSR. So, HSR, Kormangla, YPR and R&R. Four different 11 batches we have. In this, in your batch, the interaction is minimum, I would say, relatively, if you see. I can see from the beginning, only three, four of you are responding. Not more than that. So, with this one, like, you know, it reflects only two things. Either you are doing something else on the other side. Okay, simply, you know, joining in the meeting and then you are doing something else. Or you are not paying attention to the glass. Because if you do not answer, if you do not respond, it means, you know, either you are getting everything. Or you're not, or you're not getting everything or anything. Or you're simply not there on the other side. Okay, so if you do not respond, you can type in, like, you can type in. And it's not like I'm talking about only for this class. This is the overall experience I'm telling you. When I take the class of HSR and YPR, no, they talk more than me. Which is also like, no, very much. But I'm not saying you people don't interact or you will don't, you know, study during the classes. But at least if you interact, it is a two way. If it is a two way communication, it will be better for you and me both. I will also understand, you know, properly what you are getting, what kind of problem you are facing. Then I can, you know, change things accordingly. If you do not interact, it will be, it would be very difficult for me and I'm not going to suffer in the last. Okay, it's you. So keep that in mind. Okay, whatever class you are having, like you're attending, whether it is, you know, chemistry, physics, maths, biology, you should interact. Right. So this you understood all of you. Correct. Leveling effect of water. One more thing you see here. Like I said in the beginning that it depends upon the solvent that you are taking. So with respect to water, these acids will have equal strength and shows leveling effect. But when you take ammonia, what is the conjugate acid of ammonia? That is NH4 plus means what from HClO4 to HClO4. To HClO, all these acids, if you dissolve in ammonia, their strength becomes equal in ammonia. And that is strength is equals to the strength of NH4 plus. And this we call it as the leveling effect of ammonia. I'll tell you, I'll tell you that once again. Okay. So I just said what that from HClO4 to HClO all these acids, if you dissolve in ammonia. Finally, all these assets will give NH4 plus. And we say the strength of these assets becomes equals to the strength of NH4 plus. Right. That is the leveling effect of ammonia. I have just given this bracket over here. Not required. Means from HClO4 to HNO3. If all these compounds you dissolve in water, finally you will get HClO plus. And this HClO4 converts into HClO plus. HI converts into HClO plus, HBR, HClO plus, H2SO4, HClO plus, HClO3, HClO plus. So whatever acid you put in water from this to this, finally you will have HClO plus as an acid in the solution. So what we say, HClO4 converts into HClO plus. So its strength equals the strength of HClO plus in aqua solution. Finally converts into HClO plus. So strength of HI equals to the strength of HClO plus in aqua solution. H2SO4 converts into HClO plus. So strength of HClO plus equals to the strength of HClO plus in aqua solution. So finally what we can say, all these acids becomes like have got the equal strength in aqua solution. And this we call it as what? The leveling effect of water. Because their strength comes at the same level. It becomes equal acidic. That is what the leveling effect of water. Sometimes I ask you this question, why HI and HClO4 having equal strength in water but not HF? HF's strength is different. Why? Because HF cannot produce HClO plus. HF cannot produce HClO plus because the HF is a weaker acid than HClO plus. So one which is weak cannot produce a stronger acid than itself in any reaction. It is always from a strong acid to weak acid. Stronger to weaker. Always. So since HF cannot produce HClO plus in aqua solution. That's why the reaction is backward and the strength of HF is different in water than the strength of HI or HClO4. Got it? Understood? The question is sometimes they say the strength of HClO4 and HI is equal in water. But the strength of HF is not equal to the strength of HI or to the strength of HClO4. For example, right? So what is the reason for that? I can give you four options on this. They can ask you and also one liner in your school exam. Explain this why this happens. Because HClO plus is stronger acid than HF. HF cannot form HClO plus but HI can. HClO4 can. Hence the answer is. Yes, understood this? Okay. Yeah. Okay. So guys next class onwards I'll tell you what we need to do. We have discussed about acid and base now. Like I said the entire chapter is all about acid base and pH. So we'll be starting next class pH calculation. So we have different different cases under which we need to find out pH. Okay. So what we need to do I'll tell you. You just have to focus on one small formula of pH which is pH is equals to minus log of H plus. So our entire objective is to find out H plus concentration. Whatever the condition is. If you find out total H plus concentration. Substitute it here. Calculate this. You'll get pH value. Okay. For pH value calculation. Some log value you must memorize. Okay. Sometimes in the exam they won't give you log values. Okay. If you log values you should know. For example, we have log 2. Log 2 value is 0.30 approximately will take exact values. I'll write down the exact value first 0.477 log 5 log 5 is 0.6 989 log log 235. You must remember if you keep this log 7 also in mind that would be better. But first three is must. Okay. For approximation we take this as 0.30. This one approximately will take 0.48. This one approximately will take 0.70 approximately and this one is 0.84 only. There's no approximation. The last thing with the help of this is the homework. You can do this with the help of this. A pH is given that is 2.1 and you cannot take help of calculator. You have to show your working also. I want to see how do you do this? Obviously with calculator you can do but you cannot use that. Okay. So 2.1 we have pH. What is H plus concentration here? This is what you need to find out. So try this and you can share your answer with me. No, you cannot use that. You can do this calculation with the help of these values. Okay. Try that. Okay. You can do it. Okay. You don't have to use anything else. Okay. Try this and once you're done, you got the answer. Share your answer with working the entire thing with me. Okay. Fine. So next class will start with pH calculation. Okay. I will share one DPP on you with you on this. Okay. That is acid base. Right. Okay. See you next class. Take care. Bye bye.