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Calculate the pH for each of the following solutions:(a) $0.10 M \mathrm{NH}_{3},$ (b) $0.050 M \mathrm{C}_{5} \mathrm{H}_{5} \mathrm{N}$ (pyridine).

a. 11,125b. 8,939

Chemistry 102

Chapter 15

Acids and Bases

Liquids

University of Central Florida

University of Maryland - University College

Brown University

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.

02:10

Calculate the $\mathrm{pH}…

04:18

03:56

03:08

05:23

09:57

Calculate the pH of each o…

10:50

session. We're going to be doing pH calculations that air involving week basis. And for this problem, we have to week basis that air referenced first and NH three ammonia, everybody's favorite and were given an initial concentration of zero point 10 Moeller. We're gonna work with that one first. Okay, so the first thing we're going to do is look up on a table and you could just type this in if you're looking, um, r k b for this one. If you're looking for you can just type in K B of ammonia on our book gives us 1.8 times 10 to the minus fifth as the K B. So our key be expression I'm going to. Right over here are KB Expression for ammonia will have unearned numerator the ammonium ion and the O H I on by hydroxide ion. And in our denominator, it'll have the molecular ammonia. Okay, so I know this value there's my k b and because this is such a small value, um, if I were to do a nice table on this, I would see that my equilibrium concentration for my NH three should be 0.10 minus some con quantity X. But since this is such a small value, we're going to say that this is approximately equivalent to 0.10 So we don't have to use the quadratic equation. My personal opinion. Avoid that whenever it's possible. Okay, so let's plug our values in 1.8 times 10 to the minus fifth equals now these two values we switched colors here. These two values are going to be the same concentration. So those air going to turn into an X squared for me X squared over 0.10 solving for X. Let me get a brighter color here solving for X. I get 0.0 0134 to That's our first step. Second step. We're gonna take the negative log of this concentration, and that's going to give me the p O. H. That equals the P O Age, which comes out to be 2.872 to 2.8 7 to 2. And then last but not least, our third step is to take 14 minus 2.87 to 2 and looking at sig figs, etcetera, etcetera. We can have two decimals in her pH. This is the pH for the first part of this problem. Okay, Our second situation were given a 0.50 Moeller solution of period in again. We're gonna look up the K B for period ing, and that equals 1.7 times 10 to the minus nine. We're gonna set this problem up exactly the same. Um, and this is even a smaller K b. So this the amount that associates is going to have even less of an impact on original concentration. So we're going to set this up the exact same weight. Whoopsie. He raised that. We're going to set 1.7 times 10 to the minus ninth equals X squared over 0.50 solving for X. I got I didn't write it down. Shoot. Hang on, Let me do this. Quick. Um, so I need to take on 0.7 times. 10 to the minus nine times 0.5 Enter, and then I'm gonna take the square rich of 8.5 times. 10 to the minus 11. Enter, I get 9.21 95 times 10 to the minus sixth. Okay, they're is Step one again. Step two will be taking the negative log of the concentration, which is 9.2195 times 10 to the minus six. And of course I need to do that now. Negative log of 9.21 times 10 to the negative six. I got my P o h of 5.35 So now, finally, I need to take 14 minus 5.35 And I got, um, running to two sig figs. I got actually, I took a little bit more on mine. I left. I'm gonna add a couple of numbers here because it's going to make a rounding difference. I didn't round until later, so I had 035 to 9. And so when I calculated my p o. H or pH, I got 8.96 and let me verify that. 14 minus 5.35 to 9. Enter. Yeah. 8.96 That's my pH. Okay, thanks for listening.

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