Ka and Kb

Hey, guys, In this new video, we're gonna take a look at the acid and base Constance. So as you guys can know from looking at the rules for identifying compounds as either acids or bases, you should realize that there's a lot more weak species out there than there are strong ones we need to realize is thes week. Species have constants associated with them, so we're gonna say here, consider a week mono product H a acid mono product just means it has one h positive. And here we're looking at how it ionized is in water. So basically, H is the acid, so it's gonna give away in H positive to the water. The water accepts the h positive. So that's how it becomes H 30 plus the acid loses an h positive, and that's how it becomes a minus. Now what we're gonna say here the equilibrium expression equals products overreact. It's remember, we've talked about the equilibrium expression before it looks at all phases of matter, except for liquids and solids, so liquids and solids will not be included. And here we have a liquid. So we're gonna ignore it when we do the equilibrium expression. So it's simply gonna become a minus times H 30 plus over H A

Now we're gonna say that K represents our acid association constant. And it basically measures how strong or weak acids are. And we're gonna say weak acids use K a week basis. Don't use K A Instead, they use K B. So this is our based association constant. What we're gonna say here is their relationship to each other. K and K B can be expressed by this formula. K w equals K a times K B. And as you realize this K w is the same k w we saw earlier in the earlier times, we saw it as K w equals h Positive times O H minus. It's the same exact kw. And we're going to say in general, the higher the K value than the stronger the acid, the stronger the acid, the greater the concentration of H plus. Now we're gonna say related to K is PK. And remember we talked about what p means. P means negative log. So PKK means negative log of K here. We're gonna say there's an inverse relationship. It's actually the lower the PK, the stronger the acid and the stronger the acid, the greater the H plus concentration now we're gonna say here is when it comes to a weak acid, we're gonna save weak ass. It tends to have k value less than one and a peek a value greater than one. Just realized we set inverse relationship. So okay, and pkr opposites. If one is up, the other one is down strong acids. Though strong acids tend tohave, Pekka is much greater than one. I mean, not PKs with K is much greater than one, and they tend to have PKK's lower than one PK that are negative. And remember, we should be able to establish a relationship between K m p k A. In the same way, we've been able to establish a relationship between H positive and pH because here we could just simply say K equals 10 to the negative p k. We could also say the same thing for PKB. P K B equals negative log of K B and therefore K B equals 10 to the negative PK. Just remember these relationships and how they affect the acidity of our compound. As long as you can remember these few quick, easy calculations, you'll be able to go from one to the other and one last thing. We could say here that the relationship from Peak to Peak A and P K B can be established by looking at this equation here by taking them negative log of K W K a n k b. We say that the equation becomes 14 equals P. K plus PKB Now that we've seen all these types of new variables and new types of equations attempt to do the practice question on the bottom here, I say If the KB of NH three is 1.76 times 10 to the negative five, what is the acid dissociation? Constant off the conjugate acid conjugate acid is a term we learned earlier. A few videos back, but here we were giving KB or has to find the acid association constant. So it's a simple conversion from one unit to another. So once you're done with that, click back on the explanation button and see how I approach this problem. Good luck, guys.

Hey, guys, In this new video, we're gonna put to practice some of the concepts you learned about K and K B. So the first example says, knowing that HF has a larger or higher K value than ch three C O h, which is acetic acid. Determine if possible, in which direction the following equilibrium lies. All right. So we learned earlier that the higher your K value, the stronger you are as an acid. So HF has, ah higher K value. So it's a stronger acid than acetic acid is. So we're gonna say H f is the stronger acid. And again it's stronger because it has a higher K value and it's the stronger acid, so the acetic acid on the product side would be the weaker acid. Now we have to say on which side is the equilibrium lie. All you have to realize here is weaker means more stable in chemistry. Weaker just means less energy. Less energy means you're more stable, and the equilibrium will always lie on the side with the weaker acid. Because the weaker acid is the more stable acid, so are weaker. Acid is on the right side here, so we're gonna say that equilibrium lies to the right. It's a simple is that first you have to know that higher K means stronger acid and then just figure out which side the weaker acid would be on. Wherever the weaker ass it is, that's where your equilibrium will lie.

now that we've seen Example one. Let's look, at example too now example to is gonna talk about our equilibrium constant when we're given different acid association constant and what we need to realize here. This is blending Hess's law with acid base chemistry. Remember, has his law. They give us known amounts for certain equations and then they ask us to find the missing Delta H or care, whatever it is for another equation. So he was saying, What is the equilibrium? Constant? So what? It's k for this for this equation cake for the following reaction and determine if reactant or products are favored. Alright, so here I tell you that the K A or acid association constant of H C N is 4.9 times 10 to the negative 10. So here we're gonna say of this equation, it's equal to K equals 4.9 times 10 to the negative and then the acid association off. We're going to say that this is called Cloris Acid HCL 02 course acid has a k off 1.1 times 10 to the negative, too. All right, so we're gonna have to manipulate the ones with known K values. So they match this top equation here. So remember, in Hess's law, what we're gonna do is we're gonna go compound by compound and see what we find them. Here We have HC n as a reactant and there's one mole. If we look down on the other two bottom equations, here goes eight. CN also has a reacting. They both look exactly the same. Which would mean you don't wanna do anything to this equation right here. You leave it alone because this h c N already matches up perfectly with this H c n Next we're gonna look to see where do we see Cielo? Too Negative. It's a reactant here. But over here it's a product. So what does that mean we do? That means we have to reverse the reaction. Your reactions become products and your products will become react INTs, So reverse it. So this becomes Cielo to minus a quiz plus h +30 positive. A quiz gives me a check Cielo to a quiz plus h +20 acquis. And when we dealt with Delta h of the past, if we reverse the reaction that would reverse the sign for Delta H. But now we're no longer dealing with Delta H. We're dealing with K. So here it's not the same operation here. When we reverse the reaction, we actually get the inverse for K. So now the new K is going to be 1/ 0.1 times 10 to the negative, too. So that's our new answer this guy manipulated. So it is gone, and then we'll notice if you keep going, See? And negative is right here. Matches up perfectly. H C l 02 matches perfectly with this HCL 02 So we're done. What we have to do next is we have to get rid of intermediates, intermediates or compounds that look alike. Except in one reaction. It's a reactant. And in another reaction, it's a product they cancel out. So here we're gonna say who are intermediates while we have H 30 plus here as a reactant. And it cancels out with this H 30 plus over here. That's a product. Okay, so they're gone. Who else is an intermediate here? We have water as a product here. We have water as a reactant. They cancel out then, are you going to do is bring down everything that didn't get canceled out. So the HCM comes down, the Cielo to minus comes down, the CN negative comes down and the HCL 02 comes down just and it doesn't matter to the order. I write them as long as they're on the correct side. And look, we just regenerated the equation we're looking for. And since we're gonna need a little bit more room, guys, I'm gonna actually remove myself from the image just for the last minute or so. All right. So as you notice, we just regenerated the equation we had up here, so we know we did it correctly, but now we have to find its equilibrium. Constant. Are you going to stay here now is the equilibrium constant just equals this k A value times this k value. So we're gonna say cake equals 4.9 times 10 to the negative times 1/1 0.1 times 10 to the negative, too. So equals 4.45 times 10 to the negative eight. So that will be our equilibrium. Constant. So we've answered half the question so far. So what's the next part. The next part is I ask you are reactant or products favored. So remember this is gonna require us remembering a few rules that we saw several chapters back. So remember, we're going to stay here if your cake is greater than one than products and the four direction are favored. But here we have the opposite. Here are cake is less than one. So that means reactant and the reverse reaction are favored. So those are the things that we can say. And if K e q equals one, they're gonna say products and reactant air both favored, and you're at equilibrium. Okay, So again, this takes a little bit of Hess's law and applies it to our new concepts of K in K B. So just remember, if they give you an equation with an unknown K value, you have to manipulate the other ones so that they give you that same equation you're looking for in the first place. That's all we had to do here, match things up, cancel out intermediates, then multiply the case. If you reverse the reaction, then that becomes the reciprocal for K. So just remember those principles You go to guide yourself two questions like this

So here we have to determine which of the following solutions will have the lowest pH. So lowest pH here really means strongest acid. If we take a look at all of these compounds were gonna realize that all of them having them hydrogen oxygen and a non metal So they're all oxy acids. So what we have to do first is figure out how many oxygen's we have remaining in all of them. The one with the most oxygen's remaining would be the strongest oxy acid. So here we have to oxygen's and one hydrogen. So we have one oxygen left when we subtract them here, we have a child. Four. So we have four oxygen's in one hydrogen. Subtract them. We have three oxygen's left, three oxygen's and six hydrogen is we have no oxygen is left here. Three oxygen's to hydrogen. So one oxygen left and then four oxygen's and one hydrogen. Three oxygen is left. So we know that we're gonna be looking at We're gonna be looking at B and E because they have the most options remaining. Now, remember the final one here It has a negative charge, so it has ah, hydrogen and it has a negative charge, which means it acts as an AMFA Terek species. Remember, it can act as an acid or base because of this anfo Terek species where you will not consider being strong acids. So here it's week, so it's eliminated here. H I 04 is a strong acid that's given. So it is our answer here. Okay, so since it's the strongest acid, it will produce the lowest pH out of the choices given.