Weak Base Strong Acid Titrations

we continue our discussion of acid based high trey shins, but in this case, we're now dealing with weak bases and strong acids. Remember, when we react a week species with a strong species, we have to use an I C F chart. Remember, that is initial change final and again, remember, when we're using an I C F chart, the units will be in moles. In this example, we have ammonia NH three, which represents a week base HBR represents a strong acid. Remember, what do assets do as its donate H plus that's gonna create NH four positive, which is guinea one h plus. So this is our conjugate acid, and we'll have br minus as the leftover ion. Now also recall that when it comes to the terms of weak base and conjugate acid they're interchangeable with, instead of saying conjugate acid, weaken, say weak acid. Because, remember, this is a positive, possibly charged nitrogen compound, which represents a weak acid, and we're moving on a trim. It gives us an H three, so this could also be the conjugate base. Okay, so just remember, these terms are interchangeable. This year represents our typical acid based titrate in equation between a week based and a strong acid. Now that we've seen this, click on to the next video and take a look at the different steps in terms of titrate shins dealing with the equivalents point.

So here we're dealing with calculations before the equivalence point. Now recall or before the equivalents point. That means they're weak. Species is greater in amount than our strong species in this case are weak based will be greater amount than our strong acid. Here we have 250 moles of our conjugate base, which is also our weak base. And let's say we have here 200 moles of the strong acid. Remember, in an I C F chart, we only care about three things the strong species, the weak acid and it's conjugal base. The fourth one we ignored here we have initially zero of our weak acid, but there are times that we could actually have something there. Remember, Look at the react inside. The smaller moles will subtract from the larger one. That gives us 0.50 moles of our contact base remaining zero bar strong acid. Here we have the addition of 0.200 moles at the end of this, what do we have left? We have weak acid remaining. We have conjugal based remaining. So we have a buffer that's left. So we have a weak acid left and conjugate base because we have a buffer. We can use the Henderson Hasselbach equation. So remember, that's just ph equals P K, which is the negative log of K plus log of conjugate base over weak acid. So that would be the negative log of what of r. K is of the weak acid plus log of our conjugate base. Over are weak acid. What? And that would help us get our pH. So again, before the equivalence point has been reached, our weak species is greater in amount. We still have a buffer, and therefore we can utilize the Henderson Hasselbach equation, click on to the next video and see what happens after the equivalence point.

after the equivalence point, we will say that our strong species, which in this case is our strong acid, will be greater an amount than our weak base. So here we could have 500 moles of our strong acid. Remember, we only care about are weak acid, its conjugate base and the strong acid. Um, let's say here, in this case we have some of our weak acid present here. Doesn't matter, because remember, we look at the react inside, only we're gonna take the smaller moles and subtract them from the larger moles. So here will have zero left of our weak base or conjugate base. We'll still have our strong acid remaining here. We add to 50 to the product side at the end here. What do we have? We have strong acid remaining and we have some weak acid remaining again. We look at Onley, the strong species, because it has a greater impact on the overall pH. So are strong acid is what we're concerned with. And because we have strong acid remaining, we would take its moles left divided by the total volume used to find the mole Arat e of our strong acid because it's a strong acid. We could take the negative log of that concentration to help us find pH. So remember, after the equivalence point, are strong species will be great on amount than our weak species. Click on the last video now to take a look at what happens when we're at the equivalence point.

at the equivalents point, we now have an equal amount of weak base and strong acid. At the equivalence point, they're always gonna have the same moles. Let's assume here that are weak acid is zero. Initially again, we ignore the fourth species at the equivalence point. Both my week, based on strong acid completely destroy each other. So at the end, they're both zero. Do the law of conservation of Mass. We're gonna have this amount being added to our product. So at the end of this, all we have left is weak acid. Now, remember, with a weak acid or weak base in order to determine Ph, we need to use a nice chart. So we would take the most left of our weak acid divided by the total leaders used in order. Determine the concentration because we're dealing with a weak acid would use the K of that weak acid, help us isolate X, and from there we determine what our concentration of H 30 plus would be. And from there we determine what our PH value would be. So remember, when it comes to an acid based filtration, we have to keep in mind the three places in terms of our titrate shin is that before the equivalents point after the equivalence point or at the equivalence point, those three places entail using different techniques to figure out what our final Ph would be.

Ah Buffer contains 167.2 MLS of 0.25 Mueller Prepon OIC acid with 138.7 MLS of 0. Mueller sodium pro panna Wait. Now here it says find the pH after the addition of 150. MLS off 0.56 Mohler HCL here, the K of propane OIC acid is 1.3 times 10 to the negative five. All right, first of all, we know that propane OIC acid is an acid from the fact that acid is in the name. Next, we should know that it's a week oxy acid from the rules that we have learned before. And even if you don't remember those rules, we know it's a weak acid because it's K. A value is less than one. Remember, if an acid has a K less than one, it's a weak acid. If a base has a K be less than one, then it's a week base. So we have a weak acid here, sodium Prepon await looks similar to it, except it has one less hydrogen that has been replaced by a metal because it has one less hydrogen. This represents the conjugate base. Finally, we have HCL hydrochloric acid which is a strong acid. So you have two weeks species reacting with a strong acid. Remember, when we have a weak species reacting with a strong species, we have to set up in I C f chart Remember, in the I C F chart, whatever a strong has to be a reactant. So hcl here is the reactant because it is an acid, it will react with the conjugate base. So we write down the conjugate base Now remember, what is an acid do an acid donates h plus over to the base So we wind up getting as our products are propane OIC acid plus n a c l also remember now since we're doing an I C F chart, we only care about three things the weak acid, its conjugate base and whatever is strong. We have initial change final remember In a nice CF chart, we need moles as the units moles air is equal to leaders times more clarity. So we're going to divide the Emil's by then multiplied them by their mole Arat ease to get our moles here. We don't care about this compound. So when I take all the leaders, I multiplied them by more clarity. I'm going to get the most of each for my conjugate base. That would give me 0.583 moles For my strong acid, I would have 0.84 moles. And then for my weak acid, I would have 0.48418 moles. Now remember, look at Onley the reacting side. At this point, the smaller moles will subtract from the larger moles. So we're gonna subtract than by the smaller moles here, which comes from our conjugate base. So what I'm gonna have left at the end of zero conjugate base. I'll still have some strong acid remaining. Do the law of Conservation of Mass. Whatever happens on the react inside, the opposite happens on the product side. So I'm adding this many moles at the end of all of this. What do we have left? Well, we have a strong acid remaining and we have a weak acid remaining. Remember, when we're comparing them to one another, the strong ass will have a greater impact on the overall pH. So we're gonna focus on the strong acid, so we're gonna bring it down and find out what its concentration is. So we'll take the molds left of my strong acid here and divided by the total volume. What's my total volume? It's each one of these and leaders added up together. Okay, So take each one of those leaders, add them all up together on the bottom. So when we do that, we get our concentration of 0.563 Moeller for HCL at this point, realize that what do we have left? We have the concentration of a strong acid because it's a strong acid. I can simply take the negative log of the concentration and I'll have my pH. So take that concentration, which we just isolated and plug it in. And that gives us 1.25 as the pH for this solution. So remember, we're doing the same thing we've been doing. We're basically setting up our I c F chart. Whatever strong has to be a reactant, it will react with its chemical opposite because it's a strong acid, it will react with the conjugal base. From there, we determine What do we have left at the end To figure out what our Ph will be now that we've seen this example attempted to the practice question left on the bottom. If you get stuck, don't worry. Just come back and see how I approach that same practice question.

calculate the pH of the solution that results from the mixing of 75 MLS of 750. Mueller sodium acetate and 75 MLS of 750.150 Mueller acetic acid with 0.25 Mueller of hydroponic acid. Here we're told, the K of acetic acid is 1.8 times 10 to the negative five. So we have acetic acid here based on the rules that we know for oxy acids, we know it's a weak acid, and even if you don't remember those rules again because it's K is less than one, it is a weak acid. So we have a weak acid, we have its conjugate base and we have again a strong acid. Here we have weak and strong species reacting. Therefore, we're gonna do a nice CF chart. Whatever strong has to be a reactant. And here if since the strong acid is going to react with a conjugate base, it reacts with its chemical opposite, which is a base now, remember again, what is an acid do and acid donates H plus over to the base. So we're gonna get here. As a result, arsenic acid being formed plus an a b r. We have a nice CF chart. So that's initial change. Final? Yeah, we only care about the weak acid, its conjugate base and whatever strong the fourth species we ignored. Now remember, we need moles which is just leaders times molar ity. So divide this by 1000 and divide this by 1000. Multiply them by their polarities to get the moles hbr We already have it in moles so we don't have to do any types of conversion. Just plug it right in here for the conjugate base, it'll be 0.75 moles and then for the weak acid, it's 0.1125 moles look at the react inside Now the smaller moles will subtract from the larger moles. So at the end we'll have 0.50 zero Here on the product side, we add because of the conservation of mass Now we look at the end and see what we have. At the end of this we have conjugate base remaining. We have weak acid. Remaining conjugate base plus weak acid means we have a buffer. Therefore we use the Henderson Hasselbach equation, So pH equals P K plus log of conjugate base over weak acid. Remember, P K is just the negative log of K A plus log of conjugate base amount, which is 0.50 moles of sodium acetate divided by 0.1375 moles of acetic acid when we plugged that in this part is gonna give me 4. Plus, when we take the log of everything in here that's gonna give me negative 0.4393 added together, it's gonna give me 4.31 as my final pH. So remember, this one is a bit different from the one we saw earlier, because here we still have a buffer present. As a result, we use the Henderson Hasselbach equation. Remember, we have a buffer present before you reach the equivalence point in our acid based hi, Trish. In therefore, use the Henderson Hasselbach equation to get our final answer. So remember all the steps necessary when we're dealing with a three spots in a tight trey Shen is a before an equivalence point after an equivalence point or at the equivalence point