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Calculate the percent ionization of hydrofluoric acid at the following concentrations: (a) $0.60 \mathrm{M},$ (b) $0.0046 M,$ (c) $0.00028 M$. Comment on the trends.

a. 0,0400b. 0,25c. $0,76 y$

Chemistry 102

Chapter 15

Acids and Bases

Liquids

University of Central Florida

University of Kentucky

Lectures

03:07

A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, a liquid is one of the four fundamental states of matter (the others being solid, gas and plasma). A liquid is made up of tiny vibrating particles of matter, such as atoms, held together by intermolecular bonds. Water is, by far, the most common liquid on Earth. Like a gas, a liquid is able to flow and take the shape of a container. Most liquids resist compression, although others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly constant density. A distinctive property of the liquid state is surface tension, leading to wetting phenomena.

04:38

A liquid is a state of matter in which a substance changes its shape easily and takes the form of its container, and in which the substance retains a constant volume independent of pressure. As a result of this, a liquid does not maintain a definite shape, and its volume is variable. The characteristic properties of a liquid are surface tension, viscosity, and capillarity. The liquid state has a definite volume, but it also has a definite surface. The volume is uniform throughout the whole of the liquid. Solids have a fixed shape and a definite volume, but they do not have a definite surface. The volume of a solid does not vary, but the volume of a liquid may vary.

03:25

15.48 Calculate the percen…

07:19

Calculate the percent ioni…

04:39

02:09

Calculate the degree of io…

07:58

03:03

04:31

All right. So we are gonna need to find the percent ionization of Hydrofluoric acid. We got to do it. And with three different concentrations, a letter, A we're gonna find it with an initial concentration of 0.6 moles per leader and then for be well, do the same thing. But with a initial concentration of 0.0 for six malls per leader. And finally see, we got to find it with zero point 00028 moles per leader. Initial concentration. Okay, so we got a lot to do here. Um, so first letter A, um Now, let's make sure we understand we're gonna need when we do percent ionization. It's equal to the proton concentration over the, um that means the acid concentration. And it's the initial acid concentrations of that. Little zero means times 100. Well, we already have that 0.6 Mohler, but we gotta find this. That's what's gonna gradually work to find that one. So let's do it. So to find the proton concentration, we're gonna have to use the acid ionization constant for you can look it up in a chart or in the textbook. But it's for Hydrofluoric as a 7.1 times 10 to the negative four. That's the ionization constant. While that is equal to the proton concentration times, the an ion concentration all over the original acid concentration. But that's a equilibrium there. All the concentrations once it reaches equilibrium. So, um, let me start this way 7.1 times, right that again. And we don't know the proton or the anti and concentrations, but we do know they're the same. So we can do X Times X. Um, we don't know the acid concentration at equilibrium, but when you have a concentration and in our initial concentration, that's as big as this, which is one of the bigger numbers. You see, Um, if sound going to change much, so whatever it will be after they were equilibrium won't be much less than 0.6. So we'll just leave it as that which will make this problem pretty easy. Um, so, uh, we can just keep going here. Will do X squared over 0.6, and then we can multiply the 0.6 by the 7.1, Time said of the negative four. And we'll get we'll see what X squared is equal to. And that should be four. If you can try plugging it in the calculator. 4.26 times tend to the negative four. Okay. And then the last thing to do is square root to get rid of the square. And X equals two point old six times tend to the negative to So what is that we just found? Well, go back. It's the H plus. It's also equal to the an ion concentration. But the H plus concentration is what we wanted. So now we can go back to percent ionization, and we can use this as Rh plus on the top. So two point old six times, 10 to the negative, too divided by 0.6. So times 100 and you should get something. Um, 3.44 something. And I'm just gonna brown just two significant figures. Um, because that's what we started with. Ah, and that's the answer for later. A Let's keep track of these. Gonna go up here and I'll write our percents in green. So we got a nice small percent for that one. Okay, on to a letter B. So here we're starting with a 0.0 for six concentration. So we know what we got to do. We got to find that proton concentration. So let's do this acid ionization constant. We know that these are both going to be X. And, um, the thing that's going to make this one harder is 0.0 46 is a small enough number that we can't just use that as our equilibrium we have to take into account that it's gonna be this minus whatever exes. Um, what? You make the problem a little hurt, But just bear with me something you gotta do some time so we can still use that. That's always love Hydrofluoric acid concert. But now we're going to have Teoh um, multiply both of these numbers by the 7.1 soul. It's, um, get that figured out. First, let's the X Times X Let's just make that next square. And if you do the that's a 3.266 the 0.46 times a 7.1 and then you can just subtract, not just expert 7.1 times 10 to the negative four X you're distributing. When you multiply, you should know how to do that. Now, um, we're gonna turn this into a quadratic type of equation because it's gonna be set it up. So that 7.1, I'm sending the negative four axes, your second number, and then you can just subtract 3.266 times 10 to the negative six, and then that all equals zero. And yes, I'm really sorry, but you must do this quadratic equation. Um, I don't know how much practice you have doing this, but it's really just knowing what your ABC is and then plug in the numbers in. Unfortunately, we got some really big numbers plug in here. Um all right, So if case you needed that, that's the quadratic formula. So now A, this is your A is one B is a 7.1 time soon. Like Ford C is negative. 3.266 times 10 in the next six, and I just plug everything. So X equals negative 7.1 times 10 to the negative four plus minus, and we're gonna be squaring the 7.1 times 10 to the negative four minus four times, one times the negative. 3.266 times, 10 to the negative six. Okay. And that's all divided by two times one. Now, to save time, I'm going to I'm just gonna calculate all that. You should make sure you know how to do that, though. But let me jump to that negative 7.1 times 10 to the negative four. You should end up with a plus minus. If you did all that work that I just underlined, you should get three 0.6 bait times 10 to the negative three goodbye to all. Right now, because of the plus minus. Of course, you're gonna have to different answers, usually ones positive ones. Negative. So you just keep the positive answer. So this one's either gonna be one point for 85 times. Tend to the negative three War negative. 2.195 times. Negative. Three. So it's nothing hard when you see a negative. Just okay? Don't need that one. So that's what I'm using. So what is that that I just circled? It is your, um Is that before God? Concentration? All right. So let's get the percent ionization for that just abbreviate here. It's going to equal one point for eight. Five times, 10 to the negative. Free. We worked hard to find that number, and then we can use the original number. We were given 0.0 046 more times. 100 round 22 significant figures. And you should come up with 32 percent. All right, 2/3 of the way there. So let's keep track of these. So this one is equal to 32% you're seeing. It's a big jump from a to B. Um, so now stick with me. We've got letter C. So we're given 0.0 to a Waller. So another very small, even smaller initial concentration. So whatever x times the X divided by and this is so small. So we can't really use it as our equilibrium concentration. We have to subtract X, um, and that all equals 7.1 times 10 the negative four. Okay, so if you do it, we did. I let her be next up of the X squared equals 1.99 times 10 to the negative seven. Um, yes, and then minus 7.1 times 10 to the negative for X and then get it set up so we can give it the quadratic treatment. Plus 7.1 times 10 to the negative. Four X minus 1.99 times 10 to the negative seven all equal to zero. Uh, okay. I won't write out the quadratic equation again. Um, but look it up if you need to. But if we plug everything and we should have negative 7.1 times 10 to the negative four plus minus square root, uh, was make that long. Um, 7.1 times, 10 to the negative. Four squared minus four times, one times negative. 1.99 times. Tend to the negative seven. Okay. And that's all over two times one. All right. So, like, last time, try doing all this in the calculator, you composites. Um, see what you get. And, uh, I'm just gonna skip to that part plus minus 1.14 times 10 to the negative three, all divided by two So x, little equal to 0.1 five times to the negative four or a negative number. And of course I wrote that just so I can show you that you cross it out. But, um, now we know this all that work to get the proton concentrations at equilibrium. So let's go ahead then and plug it in. Percent ionization Well equal 2.1 five times. Turn negative. Four 0.2 h times 100 which will give you 77 percent. All right, finally. So letter C is 77 percent. So what do we say about this? Well, as our initial concentrations decrease, our percent ionization increases. Okay? And it's what you should expect because when there's, um, less so like, uh, here. I know this is already pretty long, but if you've got HF think of it this way. It's going from one particle to two particles each plus after negative. And if you start with a very small if this concentration is small, then um, it's gonna tend to lionize a lot more readily so to to make more particles there, there's like a need for more particles less You have. Um, but basically, it's obvious you concede that as long as you understand, that trend is initial concentration decreases percent, ionization increases, and you should be all set. All right. I hope that all made sense and good luck

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