 Just because we have discussed about P.M. calculation we have done, no? Yes. Okay. Let's write down salt hydrolysis. Salt hydrolysis. Okay. Salt hydrolysis is what? Suppose you have an acid at A plus in the base BOH and the reaction it gives what? PA plus H2, where this PA is a salt. PA is a salt, correct? So hydrolysis of salt means what? When you mix water into this salt, the reaction should go in backward direction. Okay, that is what we are talking about. It is a neutralization reaction, acid base reaction is what? Neutralization reaction. Hydrolysis of salt is what? The reaction of salt plus water. Okay. This reaction goes in backward direction. So salt hydrolysis is what we can write. Let's learn into this. It is the reverse of, it is the reverse of neutralization process. Reverse of neutralization process. So the reaction of this is what? Suppose you have a base BA. The reaction is for BA plus H2O. This gives what? This gives? Okay. PA plus BOH. Yes. Yeah. Salt hydrolysis process. It depends. In general it is exothermic. Hydrated salt if you put, it is then endothermic. But in general, it is exothermic. Okay. BA gives you this. Suppose you have a cation here, B plus plus H2O. What is the product we get here? BOH plus H plus. And analysis A minus plus H2O. It gives A or HA plus OH minus. These are the two reactions possible in hydrolysis salt. Because salt is what? Like you see, NaCl. NaCl exists as what? Na plus and Cl minus. So when you dissolve water into this, this Na plus reacts with water or Cl minus reacts with water. So in these two reactions, when this positive charge ion and this negative charge ion of the salt reacts with water, it either gives you H plus ion in the solution or OH minus ion into the solution. So when it releases H plus ion into the solution, the solution will have acidic nature. When it releases OH minus ion, the solution will have basic nature. So here also we have to find out the pH of the solution. The pH of the solution. Understood? So the first case we have, here we have four cases possible. Strong acid and strong base we can take out. Strong acid and weak base we can take. Weak acid and strong base and weak acid and weak base. In all the four cases, we have four different formula of pH. The first possibility you write down of salt hydrolysis. Hydrolysis of hydrolysis of salt of strong acid and strong base. Strong acid and strong base. Strong acid, any example? HCl. HCl, strong base? NaOH. NaOH. So when HCl in NaOH reacts, it forms what? NaCl plus H2O. So hydrolysis of this salt is what? This gives you Na plus and Cl minus ion. Right? So hydrolysis of this salt means the reaction of Na plus plus H2O and this gives NaOH plus H plus. Okay? And Cl minus gives you HCl plus OH minus. Okay? This is the cation of the salt of strong acid and strong base. Okay? Cation of the salt of strong acid and strong base and ion of the salt of strong acid and strong base. Correct? So the hydrolysis of, write down this, this is very studio. Write down the hydrolysis of the cation of the salt of strong acid and strong base, strong acid and strong base and the hydrolysis of anion of the salt of strong acid and strong base. Hydrolysis of the anion of the salt of strong acid and strong base is not possible. Is not possible. Okay? This means what? Na plus reacts with H2O. It forms NaOH, right? So NaOH is what is a strong base. In the solution, it exists as Na plus and OH minus. Complete association will present. Right? That's why this reaction has very less tendency to go into forward direction. The reaction goes in backward direction. Okay? This reaction is not possible because if initially we have Na plus, if this forms also it exists in the form of Na plus and OH minus. So Na effect is not there. Okay? That's why we generalize what? That the cation of the salt of strong acid and strong base does not go under hydrolysis. Same reason we have here also. Cl minus, this also dissociates and forms. Cl minus because it is strong acid. So this reaction also has tendency to go in backward direction. Correct? So this kind of solution is completely neutral and PN of the solution is 7 at 25 degrees. Sir, even if we change the temperature of pressure or other... Then pH will change. Yeah. Then pH will change. It could have tendency to go in forward direction. It will be neutral. It will be neutral. The reaction overall is neutral. pH will be some other value depends upon the KW value of that. The temperature according to that what is the value of pH plus PO depends upon the pH value. But overall the solution will be neutral. It won't change because whatever effect we have here the same effect we have here also. Equal number of H plus and OH minus and we will get. Both will get neutralized. Okay? Overall the solution will be neutral. Let's write down the second one. Hydrolysis of salt of wheat acid and strong base. Salt of wheat acid and strong base. We can say for example CH3 COH strong bases and COH. What is the product? CH3, COO and A CH3, COO and A CH3, COO and A plus H2O. Salt is this and this is salt of what? Wheat acid and strong base. Salt of wheat acid and strong base. What are ions we have here? CH3, COO minus and A plus. This is the cation of strong base. Hence hydrolysis is not possible. No hydrolysis for this. No hydrolysis but this will go under hydrolysis. For this one hydrolysis is possible. One thing you consider here this reaction is reversible in nature. But this reaction is not reversible. I said there are four different possibilities. Strong acid is strong base, weak acid is strong base, weak acid is weak base and strong acid weak base. All these four conditions only the first reaction is irreversible. Because this reaction has no tendency to go into backward direction. Because hydrolysis of both ions is not possible here. Only this reaction which is the reaction of strong acid in strong base this reaction is irreversible in nature. But all the three reactions are reversible in nature. Because this CS3, COO minus may react in this H2O and the reaction goes in backward direction. Understood this? Okay this is one difference you must keep in mind. Now the reaction of this with water is not here. CS3, COO minus plus H2O and this gives CS3, COOH plus OH minus What is the nature of the solution? Basic. Basic. Because we are getting OH minus I is the solution. So pH value should be what? Greater than 7. Greater than 7. pH value should be greater than 7. So when you derive the expression for pH for this you will get more than 7 value. Which is logically correct. Right? Okay. Now the concentration of this suppose I am assuming C we are getting this is 0 and this is 0 initially and this becomes C minus C H H is similar to that alpha but it is degree of hydrolysis. There is degree of dissociation. H is degree of hydrolysis. This is C H and this is C H. Okay. Write down this H is Can you write down the expression for pH for this? C H. Concentration of C H 3 C O H Concentration of OH minus divided by the concentration of if I multiply with the concentration of H plus here and the denominator also if you write down H plus What is this term? It is K dot. What is this term? K. One by K Equilibrium constant is for acid is K so one by K is this. Okay. So K H what we can write? K H. So we will find out the expression of pH in terms of K W. This is one. Now again the K H expression here we can write this as concentration of this into this is C square H square and this is C into 1 minus H. Now I am using this expression. This into this by this minus H plus here is let it be. So we can write down this and this K H becomes What? K H is the equilibrium constant of an acid. Suppose when you write down H C H, this is my example of C S 3 C O of H this is the dissociation of C S 3 C O minus and H plus. So this is the equilibrium constant how do we write? Concentration of C S 3 C O of minus into H plus divided by concentration of C S 3 C O of H since it is an acid so 1 by K is C S 3 C O of H so C H is as this equilibrium constant for this reaction is what? So this into this divided by this so this into this by this is K A stands for acid. So 1 by K is that expression this divided by this into this is 1 by C. Now if I take this assumption 1 minus H is almost equals to 1 degree of hydrolysis is negligible what is H? H is equals to K H by C and root over of it K H by C root over of it why we are calculating H here degree of hydrolysis what we have to find out? Why H? H can see for you don't have to think about that actually when you do the derivation you take the degree of hydrolysis very negligible there is no condition of when we can neglect H like alpha when we neglect alpha when it is less than 0.05 like that we don't have such conditions but when you get this hydrolysis of salt you have to assume this the degree of hydrolysis is very negligible okay so the formula will get with this only so you have to take this always it's not like alpha when we have to neglect and when we have to consider you don't have to take that H is equals to K H by C root over of it why we are calculating H here what is the purpose? why we are doing all this calculation to find out where we are calculating P H only for P H what we need? H plus H plus so many but O H P O H to neglect and then P H we can find out so what is O H concentration? H we know then we can find out this C H root K H okay so this O H concentration is C H that is why we are calculating this okay so the concentration of O H minus is what? the concentration of O H minus is equals to C into H which is nothing but root over of C into K H and what is K H? K W by K A because this K and K K W you know already K will be given in that question okay so this is equals to C into K W by K A okay this is concentration of O H okay what is this? K H by okay now if you take minus log of which minus? both side will take log of what we get minus half of log of C into K W plus log of sorry I will take this minus log of K is it right? yeah what is minus log of K P K minus log of K is P K and this we can write C plus K minus half of log C plus or minus half of log K W minus P K log of K W is what? I had 25 degree Celsius K W is 10 to the power minus 14 I had 25 degree Celsius K W is what? 10 to the power minus 14 so we can substitute this here become 7 plus half is there half of P K multiplied I forgot to give write a bracket so this becomes what? 7 right? so can I write this as 7 minus half of log C sorry log C minus P K 7 minus half of log C minus P K so what is P O H minus log of O H minus is P O H P O H is equals to 7 minus half of log of the concentration of what? what is C here? C is the concentration of C S 3 C O minus means the concentration of what? concentration of acid that you get C S 3 C O what? second last step 7 minus half should be plus is it? plus 1 okay so I write down this 3 plus log this is the expression for P O H you see P O H is getting less than 7 when you substitute you will get less than 7 P O H what is P H then? 14 minus P O H 7 plus half of this 7 plus half of this too strong base is strong so it will make the solution weak acid and weak base we have to solve that weak acid we will do that also we will do that derivation we will see the expression what we will do is it here? one thing is very important here I will write down the reactions first the reaction was this C S 3 C O O H plus N A O H C S 3 C O O N A plus N A O H now in this you see if you take 5 equivalent or molar any concentration term you can write this as it and 3 equivalent of this base ok 5 and 3 equal equivalent we do not have the number of equivalents of acid is more than that of base then what is the number of equivalent of solid form here 1 reacts with 1, 2, 3 reacts with 3 and N O H won't be present in the solution then what is the limiting reagent here how can you fly limiting reagent when it's weak but N A can't get hydrolyzed no but it's like that and 1 equivalent should react with only 1 equivalent this reacts completely how many equivalent of this or concentration of this left 2 equivalent of this left and 3 equivalent of solid forms ok so what is the pH of this solution we cannot use this formula actually this formula we cannot use however it is a reaction of weak acid in a strong base because this solution is a buffer solution you know what is buffer solution buffer solution forms by the combination of a weak acid and it's salt with strong base what did I say weak acid and it's salt with strong base so this is a weak acid salt with strong base because in this solution you have this C S D C O H present and it's salt with strong base also present this solution is now behaving as a buffer solution so we can increase the acidity and utilize the acidity it has tendency to resist the change in pH of this solution when you add a small amount of acidity so next topic is buffer solution we'll discuss that over there but the point is you cannot randomly use this formula you have to check the concentration of acid and base that you are using if it is 5 and 5 okay if it is 5 and 5 if it is 5 and 5 then this and this reacts completely now there is no more acid present into the solution we have only salt then we can use the formula of salt hydrolysis so super if I have everything react completely then there is no buffer solution no it's not for buffer solution like I said there are three types of buffer solution one is when weak acid and salt with strong base is present that forms a buffer solution so when these two reacts completely there is no acid present but we have only salt then we use the formula of salt hydrolysis not the buffer solution formula how do you solve buffer solution buffer solution we'll discuss so this you must take care of you just cannot use the formula of this in when you see the reaction like this you have to check the concentration of acid and base and then accordingly you can apply the formula it's a question actually need maybe okay if you use this pH value pH formula you'll get an answer there option for the formula right so that's what I said in the beginning you have to identify half the condition and what formula you have to apply for pH okay wait sir if it was 3 minutes then what are we supposed to do if any of which was 3 minutes that comes in the buffer solution acidic buffer that is so we'll discuss in buffer solution separately after salt hydrolysis okay so that we let it be now