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what is buffer? The buffer is a solution that can resist the pH change by neutralizing the added assets or, at the basis. So, for example, ascetic acid and sodium as time. If I the soul sodium acetate, what I'm going to get is the sodium part and the estate part. And if I the soul well, it's not this solving. But if I make an acre solution with ascetic acid in water, what I'm going to get is going to be H 30 plus plus C two h 302 Now this estate missy is the same estate that we get from sodium estate. So what we have here is an acid and its conjugate base, but they both are present sufficiently enough that if an acid is added into the solution this base, the contract base is going to neutralize that acid. However, if a base is added into the solution, this acid now is going to be sufficient enough to neutralize that. For example, if you add sodium hydroxide into aesthetic acids, what we will have is going to be water plus the conjugate base. If we add an acid into the solution like HCL to the conjugate base part. What will happiness? It will give us the conjugate acid an assault. So the entire reason why we have buffers. ISS If there's a drastic change in a pH, like if he had a continued that had some solution in sight. If you dropped here, Cem HCL, this pH would drastically change towards left on the pH scale down seven because we're adding a C l and acid and nothing is neutralizing it. Whereas if we added base, for example, sodium hydroxide now that will shift on the right hand side. But in a buffer we have both the acid and its conjugate base together, So whenever a base is added, the asset is neutralizing it. And whenever and acid is added, the base is initializing it. Let's say we have the rest of the gas. It h see you too H three 02 And we just sold this in water. Resulting equilibrium is going to be H 30 plus, since it's an acid plus C two h three 02 minus. Now let's say I also have in this solution adding n a C two history all team Well, what happens is Since this is assault, we get an A plus that, say strong basis cat ion. So this is initial and we have C two h three 02 minus. And this is basic and I on since the country could off. This is the acid acetic acid. And let's say initially I had 0.1 Mueller off h c two h, b o t. And I added 0.1 off the salt. So all the salt is converted to acetate, so I'm going to get 0.1. Mueller, the reason why I'm doing this is this is creating a buffer so normally from the previous chapter, you would know if he didn't have any estate on the right hand side. What would happen is this 0.1 would decrease in in minus X amount and we would have a plus exam on over here. And this reaction would shift right. However, when I add the common ion that we call the common ion effect, what happens is this reaction is not shifting right anymore because according to delish Italia principle, we add the we increase the amount of the right hand side. So the reaction also shifts left, so this minus X semen is going to be reduced greatly. So just to make an example to teach this lecture better, I'm straight up going to start with the example. Initially, we have 0.1 Mueller off ascetic acid and sodium estate. Sodium acetate is just basically to tell us we have acetate in the solution and they're asking us what is the ph off the solution? So this is initially what we had. The change is going to be minus X plus X and plus X, and initially we had zero off ratio in the equilibrium. We'll have 1.0 minus x x. Um, that should be 0.1 my body. That's actually right. This whole thing again. 0.1 Mueller minus x and this is going to be 0.1 plus X now R k A is going to be equal to H trio concentration times C two h 302 Concentration. Do I buy h C two h three Oh team. So are K A, which is 1.8 times 10 to the power of negative five is going to be equal to a trio X see a situation 0 to 0.1 plus X divided by 0.1 minus x. Now what I'm going to do is per usual. I'm going to assume this exes are not important. So I'm going to find X to be equal to 1.8 times 10 to the power of negative five. Then I can just check my assumption 1.8 times 10 to the power of negative five. Divide by 0.1 times 100% would give me zero point 0 18 percent, which is acceptable smaller than 5%. So then I'm going to continue. This is going to be our H 30 concentration. Since it is the X 1.8 times 10 to the part of negative five, and I will say minus log off H 30 equals two minus log off 1.8 times 10 to the part of negative fire. So my Ph is going to be equal to 4.7 to 4, and the next video is What we're going to learn is that the Henderson and Hustle Bloch equations, which is going to make our lives very easier, so we won't have to deal with this, minus taxes and plus taxes in buffer solutions. Writing our general acid equilibrium for an asset h A. In water equilibrium goes we have a minus plus h 30 plus. For the previous question, we had the ascetic acid and sodium estate. What we had was a k a equal to the A minus. C two h tree 02 and h trio Do I buy h A. Now? If remember, we had 0.1 off the sodium estate and 0.1 off h A, so they would just cancelation. So what I would see would be, say, a equals two h g o concentration. Actually, a trio constitution equals two. Okay, because the K is a fixed value, whereas ratio is our kind of variable that changes 50 concentrations. So if I want to drive an equation for this, how can I show it? Let's try to show h 30 plus. Concentration would be equal to okay, h a divide by a minus. I'm going to take logarithms off both sides. Log H 30 plus concentration be equal to log K A. H. A concentration. Do I buy a minus concentration. Now, if you remember, um, this multiplication in the logarithms means adding, so viel how Look h 30 plus vehicle to log K A plus log h a divide by a minus. And from this, what I'm going to do is I just want to multiply both sides by a negative one. So I will have minus log off H trio on the left hand side, which means ph so minus log off h three or plus will be equal to minus log off K A minus. Log off H A divided by a minus. So from this step, I'm just going to write P h on the left hand side and on the right hand side, I'm just going to call this minus log as p k a. Because if you remember minus log, something means p something. So I have Pete, okay? And I'm going to say, Plus now, instead of using this minus, I'll use Plus because what I want to do is now this logo item inside off h A over a minus would flip how this works from math. If you can remember, log off extra pour off. Negative one equals two minus log off X. So if I get this negative value to the power off negative one that basically would flip my eggs basically log one over X would be equal to minus log X, so this will be log a minus and h A. So basically, this formula tells us pH value equals two PK value, plus logarithms off the contract base divided by the acid. When we add acid or a base into a buffer, the buffer solution resistance change. However, there is still a little bit of a change in the pH. So there are two ways to calculate that the first one is that still chemistry calculation. You basically are calculating how the edition changes state relative amounts off assets and the country basis. So, for example, if you have H plus and a minus that would give us our main acid H eight before edition off the acid. Let's say there's zoo and let's say you have 0.1 Mueller off the salt. Basically, just they are conjugate base, and we have 0.1 off the acid. Let's say I'm adding an acid, a strong acid like HCL, so Edition is going to be, Let's say I'm adding just your point. Israel 25 Mueller off this What happens is this is going to get consumed with a minus. So how that would happen is straightforward. After consumption, do you get back to zero and we're going to consume 0.0 25. So we'll have 0.0 75 off the conjugate base and we'll have zero points 12 and five off the acid. So taking this model is an example. Let's say I have equal Emma's off H A and a minus. If I add mawr acid inside, what will happen is the H A is going to increase, whereas a minus is going to decrease the amount that H A is increased. If I add O. H A Bays into the solution now, what will happen? ISS H A is going to decrease, and that was a bad block. Now a minus is going to increase the same amount that we added. Always in the next method, we're going to talk about the equilibrium calculation for such additions, off assets and basis from the previous still chemistry calculation. He had the hate H a plus the water in equilibrium. It's a minus plus h trio. And if you remember, what we did was we had the h A concentration. You had h 30 plus concentration and we had a minus concentration. So initially we had zero point 1 25 that we found from Stoke Geometric Calculation and we have zero off ratio and 0.0 75 off a minus. Now what will happen is since desire in a good re, um, these were going to be there's going to be a change off minus X plus X plus X And in the equilibrium, what I'll have is 0.12 and five minus x x 0.0 75 plus x. So if I want to write to K what I'm going to write? Yes, h 30 plus a minus. I don't know why I put a little Hey, Plus over here that is an A minus, and this is going to be divided by a change now that will be equal to X times 0.0 75. Do I buy to your 0.1 25 notice that we're canceling thes small changes. So my ex concentration would be equal to H 30 plus and that will be equal to say, a times 0.12 and five do I by 0.75 So if I knew the k value, I could find the HBO concentration. And what I want to do is I want to integrate this in Henderson Hasselbach equation. So how I can do that is h a concentration. Do I buy a minus? Concentration would be equal to now. Concentration means number of moles off H A. Divided by the volume multi container number of moles off a minus, divided by the volume of two container. So I can just castle the volumes. I can't just right and h a Do I buy and a minus. So in the questions, when we see our Henderson hustle back a question what we want to do is to basically just, uh, right this volumes instead of writing the total concentration. What we would have is our equation. P h equals to Pete. Okay. Plus log off a minus. Do I buy H A? So what I would do is to get these values from still killing mystery calculation and just write them in here For a it would be 0.75 and for HIV it will be zero point one 25 so far Previously. We learn how to calculate the pH changes that has an asset and its conjugate base as a buffer. So this time, instead of having some H A and A minus, I'm going to have the base and it's contacted Asset like NH Tree. And as a contacted asset, I'll have NH four c l And remember, this gives us NH four plus plus cell minus and R C. L is initial and I on because it is the base off the strong acid. So if we have a buffer contains the base and its conjugate asset, what do we dio basically going to do? The same exact thing that we did with Hustle Black equation. It's just let's remember what our hustle black equation was. P H equals two p. K A plus log off base. Do I buy the assets now? The problem we have here is we do not have the p k a value in the question. Instead, they're going to give us not to Pete, but decay be value because we're dealing with a base. If we were dealing with an asset, they will give us a K value. So what we want to do is the following. If you remember my que a times k B be equal to 10 to the power of negative 14. So if I take minus log off both sides, I would have minus log off she a times KP that will be equal to minus log to the 10 to the power of negative 14, which is 14. So minus log off K times K B in logarithms. If you have multiplication, we simply write them as additions minus log off K A plus minus. Log off K B equals to 14. So that means P K A. Because minus log off K S P K plus, my slog off KB is p K B equals to 14, so my p k A would be equal to 14 minus p k b. Now I'm going to get this value and substituted into my equation over here and sold the rest the way we already learned

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