 So, let's try another problem. We'll use Daltham's law to figure out the mass of an insoluble gas that we collect over water. Okay, so this would be like an experiment that you would do in the lab. So, let's try this one. It says calculate the mass of hydrogen gas collected over water if 156 mils of gas is collected at 20 degrees Celsius and 769 millimeters of mercury. And they give you the reaction equation that you're using to make your hydrogen gas. So, if everybody sees that hydrogen gas is coming off of this reaction. The reaction equation is just in there to kind of throw you off. It doesn't help you at all with this problem. Okay, so you're actually going to be using in this case, as you might imagine, since every problem in Chapter 9 had something to do with pv equals nRT, right? You're going to be using pv equals nRT. Remember, we talked about Daltham's law too. So, Daltham's law is partial pressures, okay? So partial pressure of A plus partial pressure of B, so on and so forth equals the partial pressure of the total, okay? So, it gave us the pressure of total pressure. It gave us the temperature on volume. So, if we're using pv equals nRT, then that means, well, we're going to have to use R. And of course, that's always going to be given to you, 0.0821 liter ATM per mole Kelvin. And remember, when we write that out, it gives us the idea of which units we want our units of all the other variables to be in. So milliliters, we're going to have to convert that to liters. Is everybody okay with that? Yeah. So when we do that, okay? So that's how many liters of hydrogen gas we have. So the temperature of the atmosphere, the temperature of the system is also going to be the temperature of hydrogen gas. So we can just take this 20 and convert it to Kelvin. So that would be the temperature of H2. So the pressure total, that's not the pressure of H2. Is everybody with me on that one? So we're going to have to use Daltham's law. So in this case, the pressure total is going to consist of two gases. What two gases would they be in these types of experiments? One would be what? Hydrogen. Yeah, definitely. But what would be the other one? Because it said you're doing this collection over water. So what would the other one be? Water would be the other one. But was the pressure of water given to us in this problem? No. So remember there's that table that I want you to look at. So everybody look at the table, tell me what the pressure of water is. Yeah, 17.5 millimeters of mercury. So that's where you get that pressure from. So that has to be given to us. So let's figure out the pressure of hydrogen gas. Is everybody okay with that? So let's do that before we convert it to ATM. Okay, so the pressure of hydrogen gas is going to equal the pressure total minus the pressure of water. So the total pressure was 769, let me know. Is anybody doing this one with me? Remember, like your rovers and stuff. I don't expect to lose weight if you don't do the rovers too. Okay, so this is correct for the partial pressure of hydrogen gas. Okay, but we want that into ATM. So how do we convert that? You guys can help me if you know. Again, if you don't know it's something you should know. So I get for the pressure of hydrogen gas, is everybody okay with doing that? Okay, wonderful. So I'm going to erase this portion of the problem. Can I erase that? Active this morning, huh? Okay, so what do we want? Out of this problem, if you guys remember, it's the mass. So we're going to have to first figure out the number of moles. So everybody okay with that? So let's rearrange this problem. So when we're talking about in particular hydrogen, we got to think about the pressure of hydrogen, the volume of hydrogen, the number of moles of hydrogen, and the temperature of hydrogen. So volume of hydrogen, yeah, we got that. That's going to be the total volume. Same thing. The temperature of hydrogen is going to be the temperature of the system. Well, the pressure of hydrogen, we got that. And well, we're looking for the number of moles now. Okay, so number of moles of H2 is going to be PV, the pressure of H2, times the volume divided by RT of H2. Like that. So pressure 0.98918 times the volume, 0.156 liters. Oh, we're not getting on the camera. Are we? Good. Okay, we got plenty of time. Okay. So R, remember I like to expand R so we can cancel our unit down. So 0.0821 liter ATM per one mole Kelvin, like that. Okay, and then the temperature of hydrogen is going to be, well, 293. Does everybody okay with doing something like that? 8am cancels with 8am, liters cancels with liters, Kelvin with Kelvin, moles goes up to the top. So, calculate that one together, 293. So the number of moles I get is 6.41 times 10 to the negative 3 moles. But it doesn't want moles, it wants the mass of hydrogen. So remember hydrogen is H2, it's diatomic. Okay, so it's not just one H like on the periodic tables. So the moles of H2 is that. So to figure out the mass of H2, let's just write it here. The mass of H2 is going to be 6.41 times 10 to the negative 3 moles H2 times 2.016 grams of H2 per every one mole of H2, like that. Well, so that would be 0.1129 grams. Let's do it in milligrams so it'll be a little more easy to think about. So how do we do that? Convert this from 1 gram, 1000 milligrams, like that. So when we do that, it should be 12.9 milligrams of hydrogen gas. That is how much mass of hydrogen gas you collect over your work. Is everybody okay with using Dalton's Law in conjunction with the ideal gas law? Okay. So watch that video if you need to. Any questions on it? Okay, wonderful.