 heading right on buffer solution. What is buffer solution? First of all, we need to understand this. See, there are few solutions, like we have some examples in this, which always tries to maintain its pH value, right? Like if you add some amount of acid or base in that particular solution, the pH change is not that great. We'll have some change, but the change is not that high. Very small change will be there. Like for example, if you see, if you look at the example of blood, correct, blood contains carbonate and bicarbonate buffer. Okay, let me write down this. Blood is an example of buffer solution. Don't write this way. It is a buffer of carbonate and bicarbonate. We'll have the combination of these two present, which forms a buffer solution. pH value of blood, if you see, pH equals to, we have 7.4 for blood. It is slightly basic, right? Slightly basic. So this combination, whichever way it works, so that the blood pH is maintained at 7.4. By any means, if the pH changes, right, you will have some health issue, like you'll get some fever or something like that. So you need to maintain the pH of the blood again. So for that, you have to take some, in that case, you need to take some medicine, right? So other examples also we have for buffer solution. Buffer solutions are the solutions which always try to maintain its buffer, its pH value. If you add some acid or base into buffer solution, the change in pH is not that great. It tries to, there will be some equilibrium shift, and it tried to maintain its pH value. I said that it tries to maintain, right? It's not like the pH change is not there, but the pH change would be lesser than the change that would have occurred had it not been a buffer solution. Okay? When suppose you have a normal solution, you have buffer solution, and if you add a small amount of acid or base into both solution, then non-buffer solution will produce more pH change, right? You'll see pH change in non-buffer solution will be more, but in buffer solution it is very less. That is what the meaning of this. Many examples here, like I said, buffer blood is also an example of buffer solution in shampoo that we use to wash our hair. Shampoo also, we have citric acid and sodium citrate shampoo. Like you see the example of shampoo because detergents contain some basic, you know, group or we can say it is slightly basic in nature. So shampoo, which contains citric acid, sodium citrate. This is the buffer we have in this. So it tries to maintain the pH of the shampoo, which is also slightly acidic. This is slightly acidic in nature. So we have other examples like enzymes, also we have all the baby lotions. They also have, you know, this kind of a solution so that the pH will be maintained, okay? In textile industry, if you see the drying processes use buffers to maintain the pH, okay? Basically buffer we use to maintain the pH of the solution, correct? There will be some change in pH once you add acid and base, but the change is not that great. So write down first of all the definition of it. Buffer solution, it is a solution which resist the change in pH, resist the change in pH when a small amount of, amount of acid or base is added to the solution. It's called buffer solution. Copy down this first, okay? Copy it, all of you finish this. I'll dictate you two points over here. Yeah, next line you write down. This does not mean that the pH will not change. This does not mean that the pH will not change. This does not mean that the pH will not change, but it means, but it means the change in pH but it means the change in pH would be, change in pH would be lesser than the change, lesser than the change. That would have occurred lesser than the change that would have occurred had it not been buffer solution. Yeah, I'll repeat again. Wait, let me finish this. That would have occurred had it not been a buffer solution. Okay, I'm repeating the whole sentence again. I said this does not mean that the pH will not change, but it means the change in pH, the change in pH would be lesser than, would be lesser than the change that would have occurred would be lesser than the change that would have occurred had it not been a buffer solution, a buffer solution. Copy all of you. Anybody want me to repeat again? Okay, I guess all of you have written. Why? This is the definition of buffer solution. Okay. Example, two examines I have given you can write it down. Now, there are three types of buffer solution. Mainly we have two, but they are totally that three types. Heading right down, types of buffer solution, types of buffer solution. Buffer solution, if you see, we have a three types total. The first one is acidic buffer, acidic buffer. It is the solution of right down. It is the solution of weak acid, and it's salt with strong base. Could you give me an example of this? Weak acid and it's salt with a strong base. Any example, could you give me? Yes, CS3-COOH and CS3-COONA. Now, HCl and NH4OH is not possible because HCl is a strong acid, and NH4OH is a weak base, but it is weak acid and it's salt with a strong base. Okay. So, basically, if you have this reaction, for example, I have taken a weak acid, CS3-COOH means the combination should be this. CS3-COOH and CS3-COONA. If this combination is present in the solution, then the solution behaves as a buffer solution. Yes, common ion is required. We'll discuss the mechanism one second. Okay. This combination, if present in the solution, then the solution behaves as a buffer solution. Okay. Listen to me very carefully, all of you. Okay. Here, you will understand that why in salt hydrolysis, we are taking equal equivalence. Okay. How do we get this mixture? We can get this mixture if you take a weak acid, CS3-COOH and a strong base, say NaOH. Isn't it? If you have this reaction, then this two forms a salt, which is CS3-COONA and water, H2O. Like this, only we'll get this combination, isn't it? You need to take this acid CS3-COOH with NaOH, isn't it? This is the way you should get that combination of CS3-COOH and CS3-COONA. Can I respond? Right? Now, you see the same reaction we had discussed in case of salt hydrolysis of weak acid in a strong base, isn't it? Same reaction was there. Correct? So first of all, how do we differentiate that we need to take the condition of salt hydrolysis or we need to take the condition of buffer? Are you getting this, the problem you are understanding, right? Because in the question, you need to analyze first. They won't mention all the time that this is a buffer solution. Yes? So if the same reaction we have in case of salt hydrolysis and buffer solution, then how do we differentiate the two conditions or two situations, whether it is an acidic buffer or it is in basic buffer, sorry, or it is in salt hydrolysis? So for acidic buffer, we know we must have this combination, isn't it? So this combination will be there when this is present in the reaction suppose takes place. This NaOH gets neutralized completely. We have some amount of acid left and some amount of salt. Obviously, it forms because the reaction is taking place. Right? So for this, the condition is what? The condition is the number of equivalents of acid here must be greater than the number of equivalents of base. So for this one, I'll write down for acidic buffer, for acidic buffer, the condition is NaVA should be more than NBVB so that this NaOH behaves as a limiting reagent. It gets consumed completely and after the reaction gets over, still we have CS3-COOH left in the solution. And obviously, when the reaction has been done already, some amount of salt is also present over there. So we have the combination of this and this in the solution and in that case, the solution is an acidic buffer solution. Is it clear to all of you? Is it clear to all of you? All of you please respond. Okay. Now you see if this is like the condition for salt hydrolysis is what? This two must be equal. If this is equal, then it will get neutralized completely. We don't have acid or base left in the solution. It is only salt and water. So that's why we have salt hydrolysis case always over there. But when we have this condition, then it is an acidic buffer. You need to apply the pH formula for acidic buffer solution. I hope it is clear with all of you. Isn't it correct? So if you want to find out the pH of this buffer solution, we'll have the reaction here CH3-COOH because H plus will get from this only. CS3-COOH and then CS3-COOH and here we have. So we have only this reaction which gives H plus. So we need to consider this only. Other one is salt. Other one also I'll write down. CS3-COOH and NA gives CH3-COOH minus and NA plus. So in this two we don't have H plus. So we cannot consider the second reaction to find out the pH expression. So from the first one, if I write down the expression of K, this would be concentration of CH3-COOH minus H plus divided by CH3-COOH. Remember, this CS3-COOH minus is the salt. It's coming from the salt. Right because this too has one common ion. So this will suppress the dissociation of this acid because of common ion effect and hence mostly this is present because of the dissociation of salt not because of acid. Because it is already a weak electrolyte, dissociation is less and then also we have one common ion. So this common ion also suppress the dissociation of this. So concentration of H plus if you get here, this would be K into concentration of CS3-COOH, concentration of CH3-COOH minus. If you solve this and calculate pH, so pH I'll write down the formula here. pH is equals to pKa plus log of salt by acid you will get, salt by acid. So this is the expression of pH. Once you got this thing that it is a buffer solution, you have to apply this formula. Correct? Second point, this value you see here, log of this term, this is the change in pH we have actually. Like I said, the change in pH is very less. So whatever the change, if they ask you to find out the change, you need to find out log of salt by acid. We will discuss one questions on this in the next class, not today because we have to discuss few more things. But one or two problems we'll see, you will understand how to do this. But always keep this in mind, acid, the original pH is, we'll get according to this K value. But this K value is not changing but because of the acidic buffer, we'll have little bit change in pH and that change would be this and this. No, this is, one second guys. Yeah. Yeah, I'll discuss about this one second. So this is the pH we have. See, this salt is CS3CO minus here. This is salt. Like I said, it is coming from the salt only and this is acid. Just you take minus log both side, you will get this expression. You can try it. Take minus log both side, minus log of H plus is pH. This is minus log of K plus minus log of this. So if you revert it, you'll get minus log means you'll get plus log over here. You'll get the same expression. Think about it, you'll get it. Yes, that's what I said. This salt dissociates like this and this further won't let dissociate this weak electrolyte because CS3COH is a weak electrolyte. So this won't dissociate much initially. So hence we say that the CS3CO minus mostly it is present because of the dissociation of salt not acid. So this CS3CO minus we are considering this as salt and this is the acid only. We get this. Correct. Understood. This equation, we call it as Henderson's equation. Not important, just a name. Henderson's equation. Okay. So this is the pH calculation you can easily calculate from this pH of the solution. The question is next that how this buffer solution works? Like I said, it maintains the pH of the solution, tries to maintain. The change is not that great. So what happens? You consider this equation one over here. Mostly we have the change in this equation only. Once you add an acid, acid you are adding means you are adding H plus. So once you're adding H plus, this H plus is consumed by the CS3CO minus and it forms CS3CO as the first reaction goes in backward direction. Right. And whatever extra H plus you have added that combines with CS3CO minus forms weakly ionized CS3COH. Hence the extra H plus that you have given it gets consumed and pH will be maintained. Further, the dissociation of this is not possible because this common ion effect to mine. Right. So what we can write here you see just two more points here on addition of acid which means H plus we are adding. The first reaction first reaction goes in backward direction and forms weakly ionized CS3COH which can't dissociate further, which can't dissociate further due to common ion effect. So what happens? We are assuming CS3CO minus is present because of salt and the reaction is going in backward direction. So salt concentration here decreases once you add acid and acid concentration increases. We'll discuss the question next lesson. As soon as you finish this theory. Okay. How to do the question? We'll discuss that right. Salt concentration will decrease because CS3CO minus is taking H plus and forming acid. Right. So this is the reaction here. If you add a base over here means OH minus on addition of of base OH minus again the first reaction goes in forward direction, goes in forward direction, direction, direction. Okay. So in this it is Ulta. Salt concentration will get more amount of CS3CO minus salt concentration increases. Acid concentration decreases. Okay. Copy this down first. Okay. So all the biology students you just wait for two more minutes. I need to talk a bit regarding the syllabus. Right. Don't go like any one of you just let me finish this first. Okay. But biology students hold on for five more minutes. Okay. This is done. I'll copy this. Okay. See here. So once you add base, so base OH minus will take this H plus and forms H2O. So this reaction goes in forward direction forms more amount of salt and acid concentration decreases. Okay. So we'll talk about it again in the next class when we discuss the question. Okay. Did you understand this? All of you? It's clear. Okay. So we'll continue with this next class buffer. A few more things we need to discuss. Okay. So those who want to leave you can leave now. Biology students is just I want to know from you that what is the, you know, your portion left in bio.