 Okay, let's try this one, it's one of the more difficult problems. This one says, the decomposition of baking soda produces carbon dioxide gas. At 42.5 mils of wet gas is collected over water at 22 degrees Celsius and 764 millimeters of mercury. What is the volume of dry gas at STP conditions? And then it wants us to go look at the table to see what the pressure of water at 22 degrees Celsius is. And when we go look at the table, we see that at 22 degrees Celsius, water's partial pressure is 19.8. So from that, so that's what the problem is, okay? So from that, we're going to have to figure out, well, what's the partial pressure of the carbon dioxide gas to do anything? Okay, so remember it says, decomposition of baking soda, so like sodium bicarbonate, goes to something, something, something in carbon dioxide. Okay, this is what we're interested in, so we don't really need to balance the equation, we just need to know that there's carbon dioxide gas, okay? And that's going to exert some sort of pressure. So in order to start this problem, what we really need to figure out is, well, what's the pressure of the carbon dioxide gas? Like that, okay? So the first thing we're going to do is use Dalton's law to figure that out, okay? So remember, Dalton's law says the pressure total equals the pressure of partial pressure of 1, partial pressure of 2, so on and so forth, right? So we've got the partial pressure of carbon dioxide plus the partial pressure of water equals the total pressure, okay? So we just rearrange this formula to figure out, well, what's the partial pressure of carbon dioxide? It's going to be the partial pressure, or the total pressure minus the partial pressure of water. So when we do that, we get 764.0 millimeters of mercury minus 19.8 millimeters of mercury. So let's get our calculators out and do this problem, okay? Sorry to go around on your calculator. 764 minus 19.8. Okay, so when we do that, we get, I guess I didn't mean to do my calculator for that one really, but, 744.2 millimeters of mercury, okay? So are we fine with getting to that point? Yes. Okay, wonderful. Let's just write that down because we're going to have to erase all that stuff, okay? So 744.2 millimeters of mercury. So that's the carbon dioxide, and that's what we're interested in, but the problem asks us to be interested in. So is it all right if I erase all that stuff? Okay, wonderful. So now, remember it's asking us, what's the volume at standard temperature pressure? But if we look, right, what is standard temperature pressure? It's the temperature of zero degrees, right? But we're at 22 degrees Celsius, right? And it's a pressure of 1 atm, but remember 1 atm is 706, right? And this is not 1 atm, okay? So we're going to have to eventually figure that out, okay? But first, let's figure out, well, what would be the number of moles of carbon dioxide that we have right now? Okay, that's the next thing we need to figure out. The number of moles of carbon dioxide, like that, okay? So in order to do that, we have to use the equation, what equation are we going to use? PV equals nRT. Yeah, very good. PV equals nRT, right? So let's write that down to remind us, okay? So PV equals nRT. And remember, we're looking for n number of moles. So let's just rearrange this equation really quick, okay? So it's going to be n equals PV divided by RT. Very good, right? Okay, so number of moles of carbon dioxide, well, do we have the pressure of carbon dioxide? Yes. Do we have the volume of carbon dioxide? Yes. But what do we know about volume units? Is milliliters what we want to use in PV equals nRT? Liters. Liters, right? We've got to change it to liters, right? Yes. So remember what we do. We take 1000 milliliters, one liter like that, and then cancel, cancel, 0.0425 liters. Are you okay with that? Okay. So what's next? R, well, remember, R is just the gas constant that's given to us. 0.0821 liter ATM mole, okay? Yes. And so we know that, and then T, right? So that's the temperature of our carbon dioxide. Is that in the right temperature units? No. What do we want temperature units? Kelvin. Kelvin, very good, right? So what do we do? Add 273. Okay. So when we do that, we get 295 kelvin. And so now we have our units all in the correct standard units, right? Okay. So let's just plug them in and figure out what the number of moles of carbon dioxide is. Okay. So the pressure of carbon dioxide, oh, no, we don't have all our units. Okay. So what do we have to do here? Millimeters of mercury, 118. Okay. So 0.97918. Now we have everything in the right units, isn't that right? Okay. So pressure, ATM, we're cool. So 0.97918 volume in liters, 0.0425 liters divided by R, 0.0821 liter ATM per 1 mole kelvin, like that. Right? Yes. Okay. And then multiply that by 295 kelvin. Okay. So let's cancel out our units now. Kelvin cancels with kelvin. Leaders cancels with leaders. ATM cancels with ATM. And we're left with per per mole, which is mole. Right? Okay. So let's put it all in our calculator. So times 0.0425, divide that by 0.0821, and divide that by 295. And I get 1.72 times 10 to the negative 3 of carbon dioxide. Okay. Is that what you all got? Yeah. Okay. Wonderful. That's the number of moles of carbon dioxide at 22 degrees Celsius. Is that what the problem was asking for? No. It wants us to figure out what the volume is at standard temperature pressure. Okay. So what we did all that for is just to figure out this number here. Okay. So this is the moles of carbon dioxide. Okay. That's not going to change when we change the temperature or pressure. Okay. So now we're going to have to go back and do this problem all over again but backwards. Okay. So let's now erase the things that we don't need so we won't get too confused and keep the things that we do. Okay. So standard temperature pressure, what is the temperature of standard temperature pressure? Zero degrees. Zero degrees Celsius. So it's 172 degrees. Yeah. So if it's zero degrees Celsius then we're going to add 273 to that to get Kelvin. So it's going to be 273 Kelvin. Okay. The volume is going to change of course. We know that because that's what we're looking for. Okay. The pressure, well we don't need to do all this Dalton's Law stuff. Right. So what's the pressure going to be? 118. 118M. Right. So the pressure is going to be, we'll put 1.008M just so we don't forget our significant figures. Okay. So what do we got? PBN, we've got that now. Right. So let's write it a little higher up here. And the CO2 is 1.72 times 10 to the negative 3 moles. Okay. So let's try this again. P, we're looking for V in RT. Right. So we've got everything we just need to solve for the volume now. Okay. So can I erase this part here? Yes. Okay. So we're solving for volume. So rearrange this equation algebraically. It's going to be V equals N RT divided by P. Right. Okay. Wonderful. We're looking for volume. So N 1.72 times 10 to the negative 3 moles are 0.0821 liter ATM per 1 mole kelvin. Like that. T 273 kelvin all divided by P which is 1.018. Okay. So is everybody okay with that? Yes. Okay. Wonderful. So now what we want to do is cancel out our units. So moles cancels with moles. Kelvin cancels with kelvin. ATM. Very good. Cancels with ATM. So we're left with what? Leaders. Leaders. So let's go ahead and calculate this. And what I'll do, I want to convert it back to milliliters because in liters it'll be like 0.00. So we're going to convert it to milliliters to make it a more kind of easy number to think about. Okay. Anyways, so 1.72 times 10 to the negative 3 times 0.0821 times 273 and then divided by 1. So in liters, right, what do we get? 0.0385 liters, but like I said, we're going to put that into milliliters to make it a more reasonable number. 8.5 liters of carbon dioxide. So that would be the volume of carbon dioxide at standard temperature pressure. Okay. Yes. Any questions on that one? So it's a lot of steps, but it's all the steps you know, you just got to go backwards and forwards. Yes. Okay. And also use Dalton's law. So it kind of integrates a lot of things. Okay. Any other questions? Okay. Wonderful. Yeah.