 So let's try this one. I like this one too because it puts together a lot of things that you've learned already. So it says a compound has the empirical formula SF4 at 20 degrees Celsius a 0.102 gram sample of the gaseous compound occupies a volume of 22.1 milliliters and exerts a pressure of 1.02 atm. What is the molecular formula of the gas? Okay, so let's go ahead and we've already written down everything the problem gives us. So remember, empirical formula is the simplest whole number ratio of the atoms of the molecular formula. So the molar mass is going to be the multiple of the empirical formula mass. So let's figure out what the empirical mass is. So, sulfur 32.7 plus 4 times 19 is 108. 07 grams per Okay, or, well, we're going to do molar mass anyway. So we'll say grams per mole. Okay, so it's going to be a multiple of 108.07. So if you get somewhere close to that, that's the number you're going to put, okay? So what are we going to use in this equation? We're going to use pv equals mrt. So the reason we're going to use that is because we've got values for temperature, volume, pressure, and remember, r is always given to us. So r we're going to write over here, 0.0821 liter, 8m per mole. So from that, we should be able to get, and we will be able to get, the number of moles. So let's rearrange this equation to solve for the number of moles. Okay. So number of moles equals pv divided by rt. Okay, but now when we look over at the values that we've been given here, right, t, well, that's supposed to be in kelvin. Okay, so over here it's in Celsius. So we're going to change it to kelvin. So t73, so that's going to be 293 kelvin. So this is in volumes in milliliters, so we're going to change it to liters. So 1,000 milliliters for every one liter. Everybody fine with doing that? Okay, so is everybody following me up to here? Okay, and remember plug in those values if you can't just see it right away. So let's go ahead and plug and chug and get a number of moles that we have here. So the pressure is in the right units, 1.02 atm times our volume, which is now in the right units, liters, 0.0221 liters divided by r, the gas constant, 0.0821 liter, atm per one mole, like that. I like to write it like that so we can remember to cancel everything out. And then multiply that by our temperature, which is 293 kelvin. So everybody follow me to this point? So let's go ahead and cancel our units, atm cancels with atm, liters cancels with liters, kelvin cancels with kelvin. 1 over 1 over moles is going to give us moles. And punch that into our calculator. So 1.02 Okay, so the number of moles I get, very small number, as you would expect it to be, 9.37 times 10 to the negative 4 moles of this gas. So does everybody follow me to that point? So the molar mass of the gas, right? So the empirical mass is the mass of the empirical formula. The molar mass is going to be, well, on grams per mole, right? So in this case, it's going to be mass divided by the number of moles, like that, right? So that's grams per mole. Does everybody understand what I'm saying? Yes. Do you get that? Okay, wonderful. So when we look here, do we have the mass in grams? Yes. Yeah, we do, right? So let's put that in there. 0.102 grams. And do we have the number of moles? We just solved it, right? Okay, so let's put that in there. 9.37 times 10 to the negative 4 moles. And remember molar mass is grams per mole. And that's what we're looking for, is the molar mass. So eventually we could figure out what the molecular formula is, right? So 0.102 divided by that number of moles. And I get a number that's one, so it's a three significant figures, 109 grams per mole. Like that. Okay, so 109 grams per mole. Remember, the molecular formula has to be a multiple of the empirical formula, okay? So our choices are going to be 108, then the next one up would be 216, right? So which one is this closer to? 108 or 216? 108, right? Okay, so we know that the molecular formula is going to be close to that number, right? And the only multiple of that is going to be SF4. So the molecular formula is the same as the empirical formula, because if we calculated that formula, it would be approximately 109, which is what we got on this problem. Okay, does that make sense to everybody? Does that make sense to you? Okay, wonderful. So good job guys. I know it's a little involved problem. Okay, so the thing is with this one does the answer doesn't have to be exactly, okay? It's just got to be close to that multiple. Where'd you get the .821? That's the ideal gas constant. So that's something that's always given to you. Okay. Thanks, Sam. Are there any other questions? Okay.