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Determine the pH of (a) a $0.20 \mathrm{M} \mathrm{NH}_{3}$ solution,(b) a solution that is $0.20 \mathrm{M}$ in $\mathrm{NH}_{3}$ and $0.30 \mathrm{M}$ $\mathrm{NH}_{4} \mathrm{Cl}$

a) $\mathrm{pH}=11.28$b) $p H=9.60$

Chemistry 102

Chapter 16

Acid-Base Equilibria and Solubility Equilibria

Acid-Base Equilibria

Aqueous Equilibria

Carleton College

University of Central Florida

Drexel University

University of Toronto

Lectures

00:41

In chemistry, an ion is an atom or molecule that has a non-zero net electric charge. The name was coined by John Dalton for ions in 1808, and later expanded to include molecules in 1834.

24:14

In chemistry, a buffer is a solution that resists changes in pH. Buffers are used to maintain a stable pH in a solution. Buffers are solutions of a weak acid and its conjugate base or a weak base and its conjugate acid, usually in the form of a salt of the conjugate base or acid. Buffers have the property that a small change in the amount of strong acid or strong base added to them results in a much larger change in pH. The resistance of a buffer solution to pH change is due to the fact that the process of adding acid or base to the solution is slow compared to the rate at which the pH changes. In addition to this buffering action, the inclusion of the conjugate base or acid also slows the process of pH change by the mechanism of the Henderson–Hasselbalch equation. Buffers are most commonly found in aqueous solutions.

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Determine the $\mathrm{pH}…

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Calculate the $\mathrm{pH}…

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Find the $\mathrm{pH}$ of …

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What is the pH of a soluti…

Hey, everyone. So what we're gonna work on today is finding the pH of the 0.2 Mueller ammonium ammonia solution. So this is a lot of text. It can look a little intimidating. I'm just gonna encourage you to follow my green pen and I will lead you through this. I will get together. There's no worries. So the first step of this reaction is we're going Teoh, make a rice table. Start with our start with the reaction right down the balanced chemical equation of the given chemical that you have. So in this case, we have ammonia is gonna balance out with water for an equilibrium with ammonium and hydroxide. So what we're gonna do is we're gonna make note that we're only gonna pay attention to the quickest solutions. Anything that it's solid or liquid does not get counted in our rice table. So for initial concentration, we know that we have 0.2 Moeller of ammonia. We've got zero Moeller of ammonium zero Moeller of hydroxide. We're gonna change. We're going to shift to the right shift to the right so we know that we're going to subtract some number of polarity and we're going to add some number of polarity on this side on the right side and then just for simplification, we're gonna make a little equation based on those changes. Step two, we're gonna look at the K B. And that's the ionization constant of the base or acid for we got be we're gonna do base because ammonia is a weak base, the constant this is a constant value. So any time you have ammonia, you're always going to have a K B of 1.8 times 10 to the negative that so we can plug that right in and substitute the values for our equation. Here, Here's our k B. Um, we know based on our rice table that this is the concentration of our ammonium concentration of our hydroxide. And this is the concentration of Harmonia. Now, since we have a K B, that's pretty small. It's to the negative fifth and we know that our initial concentration of ammonia is 0.2 Moeller. This is pretty large compared to RK be so we can predict the X is going to be small. So what weaken Dio is cancel our X because we know that the significant figures will not change much if you don't include this. If you do include it, you have to do the quadratic formula for simplicity and time of this video. We're just not going to do it. And we're simplifying here. Um, and if you plug it into your calculator, I got approximate X is approximately 1.897 times 10 to the negative third. So that's a pretty small X. And if you look back, Step three, look back at your rice table and you plug in the X that you've got. You can see that there's not really a significant change from our X value here. You could probably around 20.2 bowler if you want to, but just so you could see the difference in the numbers, what we're looking for is the concentration of our hydrogen hydroxide ions. So we're going Teoh, take this over to our step four. Our step four is just telling us that the P. O. H. Is You can find it by finding the negative log of the concentration of the hydroxide ion. So we're gonna plug in what we found, um, in our data here on. We're gonna plug that into our calculator. And R P O. H is 2.72 and then we know that since ph. Is on a scale of 14 that whatever is not on the pH scale is going to be on the P o wage scale. So we know that we could always subtract the Pio age from 14. Do that, We're gonna subtract 2.27 or 2.72 Sorry from our pH and get 11.28 as our final pH of r 0.2 ammonia solution. So that's our part one. And we have a part to for this problem, and luckily, it's very similar. So I copied and pasted most of this. But just so you can see the difference on highlight the differences for you Um, the difference is that we're gonna have 0.3 Moeller of ammonium chloride. So that means in our rice table we're gonna have, um, uh, some value to plug into the initial value and that we know that for our equation, we're gonna have 0.3 Moeller plus X instead of just plain. That's what that's gonna dio. It's not going to change our K B because that is a constant, but it is going to change. Our values here will plug that in. So again, we're gonna look at our KB or KB A small are relative. Initial concentration is relatively large by that night itude of four. So we're gonna assume that X is small and not do the math for that because it's not going to significantly change are significant figures at the end. So here is the equation again. We can cancel this because we know that it's not gonna change our values much. We're gonna plug it in here on I got X is approximately 4.0 times 10 to the negative. When we put this into our final data table, you can see that X is very small. It barely changed the numbers at all, Um, and that we have our concentration of hydroxide ions here. We're gonna plug that into our step four like that number right in here on. We're gonna get a P o h of 4.40 for our, um, last equation. And then we're going to subtract that number that we just got 4.4 from 14 to give us our final value for R. P. Ages 9.60 p eight for our buffer solution. So this looks like a lot of text and looks like a lot of math. It's not a scary if you practice. Just keep practicing your rice tables. Keep practicing your buffer solutions and this will become second nature to you and it will not be scared, so good luck.

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