Equilibrium Constant

Alright, guys. And I want to talk about the relationship between the equilibrium constant and the PK. All right, so remember that in general chemistry, we were always talking about something called ph. Okay. And ph was used to measure. What do you guys remember? It was actually used to measure the concentration of hydro knee, um, ions in a solution. Oops. Not is in solution. Okay, so I know that's really specific, but it was used to basically measure how acidic a solution. Waas How acidic or how Basic. Okay, but it turns out that in organic chemistry, we don't care about the solution. It all. We don't care if it's acidic or if it's basic at all. What we care about is the actual molecule itself. And what I care about is how likely is that molecule to donate a proton? Or how likely is that molecule to accept a proton? PH doesn't tell me that Ph just tells me how maney H pluses are circulating in this in this test tube. I don't care about that. I care about the molecules inside. I care. How much are they likely to give away a proton? Okay, so that means that we're gonna use a different measure. We're gonna use the negative log of the equilibrium constant where the dissociation constant. Remember that dissociation constant has to do with how likely a bond is to break. Okay, so I use the negative log of how likely that is toe happen to figure out for the tendency of a molecule to donate protons. Okay. And that's what we actually care about. So that's why in in or go I mean, Jen can be used pH. But now, in Oregon, we're gonna use PK instead, okay?

So let's just talk about stuff that you guys should remember that strong acids are gonna have a high dissociation constant. That means that they're very likely to disassociate fully. Okay. And that means they fully associate in iniquitous solution. Okay, remember that weak acids are gonna have a smaller dissociation constant. And what that means is that they're only gonna partially associate in an aqueous solution. And that makes a huge difference, because that means that they're gonna have different P. K s. They're gonna have different tendencies to donate protons. Okay, now, let's remember what is PK? Well, p remember, stands for the negative Log base 10. Okay. All right. And then remember that K a stands just basically for products. Overreacted. Okay, Now, I'm not going to make you guys calculate every single thing, okay, but check it out. I mean, products in this case are just dissociating into h plus. Okay. And reactant are what happens before it fully associates. That makes sense. So the K is basically the ratio of how much of my acid is gonna actually become a proton can. That's what I care about. So therefore, if we're taking the negative log of this K A. What that means is that the higher the K A basically, the higher the chances of the molecule breaking apart and making ions the lower the p K. Is gonna be okay. So just like we had in Ph. Remember that your strongest acid was actually the one that was the lowest pH. It was close to zero. Remember that? Basically, Ph is on a scale of 0 to 14. Remember that down here was the very acidic solution. And then over at 14 was the very basic solution. Okay, remember that if it was very acidic, it would have a very low pH. And in the same way, Pekka is going to do the same thing. So your strongest acids are always gonna have the lowest numbers for Piquet. Does that make sense? And it's because we're using the negative log, not the positive. So it's always gonna be the opposite. Cool. So far awesome

now, I What I want to do is I want to go over the similarity of the pH scale and the PKK scale. So with for the pH scale, like I said, zero is very acidic. 14 is very basic, and seven was neutral. Remember that seven was just water, okay? And that was neutral is right in the middle. Well, for Piquet, we have something very similar, but for Piquet, it's just gonna be a different scale. And it's going to mean something different. So for Peak A about the lowest PK that you can get without being a crazy molecule is around Negative 10. And these were gonna be the most amazing acids. Okay, Remember that acids okay, remember that Piquet has to do with how much it wants to be an acid. Okay, so negative 10 is gonna be, like, the most amazing assets ever. And then it turns out that the scales about from negative 10 toe about 50. So 50 would be about the same thing as me saying like a really high number for Ph. And what I'm wondering is, what do you think 50 means? Do you mean that that means do you think that means that it's a very good base. And the answer is no. It has nothing to do with basis city because remember, all this is is we're just trying to see how likely is it to dissociate into an acid. So that means what is 50 50 is just going to be Pardon my French, but it's just gonna be your very, very shitty acids. Okay? It's the ones that are terrible, it associating. So basically, it's 50 doesn't mean that your basic it just means that you're really bad at being an acid. It means that you suck as an acid you're never gonna associate. Okay, then what is 16 16 is actually water and water is going to be kind of your neutral PK where basically anything above water, we're going to say that those were the good assets, and then anything below water. We're going to say that those are the bad acids. Does that make sense with 50 being the worst of all? So much so that I said she okay, does that make sense? So basically, when we're talking about PK is we're always looking at things that are lower than 16 as our strong or as our good acids. Okay,

So now what I want you guys to do is calculate the PKK's of the following acids using the dissociation constant. Okay, so in this case, I'm already giving you the dissociation. Constant. This is really easy. All you have to do is just take the negative log of it. So I'm just really like or go has very little math in it. But I just want you guys to practice this. You remember the definition of negative log. So in your calculator, what you should do is just type in and you guys can fall along with me. So maybe pause the video if you need to get your calculator. Okay. You guys all got it, or you have your iPhone on sideways. Perfect. Awesome. So what we're gonna do is we're gonna say 1.75 times 10 to the negative five, okay? And we're just going to take the negative log of that. So I'm gonna basically type in that number, and then I'm going to type in log based 10. If it says that, okay. And then I'm going to type in the negative sign. Okay? Remember that you have. You basically have, like, a positive. Negative button. Okay, on your calculator. So you're gonna type in the negative sign on your calculator. And what that's going to give you is a peek a of 4.75 Okay, so is that a good acid? What do you guys think? Yeah, that's actually a pretty good acid, because remember, I said anything below 16 is pretty good. So it turns out this is actually a carb oxalic acid, remember? Carb oxalic acid. So it turns out car oxalic acids are actually pretty good acids doll, right? That's why they're called Khar oxalic acids.

So let's try this next one. Notice that it has a dissociation constant of that slightly different. Go ahead and take the negative log of that number and see what you get. Snow you should have gotten is you should have gotten the number nine point two four if you round it. Okay? And that's the P K. So I wanna ask you guys, which of these is the stronger acid? Is acetic acid stronger or is ammonium stronger? And the answer is it has to be acetic acid. Okay, this is my stronger one, because the fact that it has a lower PK Okay, In fact, every time that you drop one in peak A, that actually means is ten times stronger because it's a log scale. So it turns out that acetic acid is actually like probably like, almost like a hundred thousand times better oven acid than ammonium. Isn't that crazy? Like the numbers get really big really fast when it comes Thio acidity. So I hope that makes sense. It's just a quick review. What's most important about this entire page is you guys knowing this trend right here where your lowest PK is gonna be your strongest acids, Your highest peak. A s are gonna be your worst acids. Never say that their bases, because PK has only to do with acids and not with basis city. All right, so let me know if I can clear that up for you in any other ways, But if not, let's keep going.