 that says your patient's oxygen tank contains 0.650 moles of gas at 730 dot millimeters of mercury pressure If you added oxygen until the final pressure was 1.15 atm How many moles of oxygen did you add to her tank? Okay, so how do we do this? Well, this hopefully you guys can tell gas law Expression guys if you don't mind gas law expression, right and in particular, it's Apagodros law So well the way I like to do these is to Take your PV equals nRT and we know that it's changing, right? So we're adding some moles to this and the pressure is changing Okay, so let's write down so well Well, let's write down the things that it gives us first and just confirm that information So it says that the original number of moles of gas Is 0.650 moles and it says the original pressure 730 dot Millimeters of mercury and then it asks how many moles of oxygen did you add to her tank? Okay, so that's going to be another series of problems that we'll have to do in a second But it tells you that the final pressure is 1.15 18 So hopefully you guys can see right that the number of moles is changing and the pressures are changing So that means plus you we're going to take PV equals nRT and divided by PV equals nRT So we put little ones at the top twos at the bottom remember R never changes so That cancels out in this case the temperature is stayed the same so that cancels out and Volume has stayed the same because it's in like a gas cylinder Okay, so the pressure has changed in the number of moles of change, so let's rewrite our equation P1 over P2 equals n1 over n2 And currently we're looking for n2 although that's not going to be the final answer Okay, so let's rearrange our equation n2 equals n1 P2 over P1 So do we have all of those numbers? Yes, but unfortunately we have these in two separate Pressure units, okay, so we're going to have to convert one of the pressure units to the other pressure unit I prefer to work in ATM, so Let's just do that Version would be given to you. It might be called four On ATM So we have the initial pressure final pressure and the initial number of moles ATM cancels, so Okay, so I got n2 as 0.778 Moles, okay, so the number of moles total this is the number of moles total that's in the gas But it asked how many moles did you add to her gas? Okay, so in order to do that, of course, you're going to have to take this number So which is the number of moles that's total and take well Remember this equation It's going to be the initial number of moles plus the number of moles that were added right, so in order to figure out the number of moles that were added right, it's going to be the total minus the initial and in this case 0.78 moles minus 0.650 moles and the answer would be 0.128 moles of gas or Opposite to where added Okay, so that's again one of those kind of problems that if you If you don't do everything I Don't think about what the problem is saying you'll get it wrong, okay? Yeah, are there any questions about this one? Okay questions