Suppose you are given two 2-L flasks and told that one contains a gas of molar mass 28, the other a gas of molar mass 56, both at the same temperature and pressure. The mass of gas in the flask A is 1.0 g and the mass of gas in the flask B is 2.0 g. Which flask contains the gas of molar mass 28, and which contains the gas of molar mass 56?

Video transcript

Welcome back everyone. We need to consider two flasks with a volume of one liter with one flask having a gas with a molar mass of 20 g per mole and the other flasks containing a gas with a molar mass of 40 g per mole. At 25 Celsius. The gas in the gas sample in flask A has a pressure of X 80 M. And a mass of two g at the same temperature. The gas in flask B has a pressure of 20.5 X 80 M. And a mass of two g. Identify the flask that corresponds to the given molar masses, 20 g per mole and 40 g per mole. So what we're going to want to recall is our ideal gas equation in which the pressure of our gas multiplied by its volume is related to the molds of our gas times R gas constant R times r temperature in kelvin. And we can interpret our moles of our gas as grams divided by the molar mass, which is then multiplied by r gas constant R. And temperature in the denominator. So with this outlined, we can see that pressure has an inverse relationship with molar mass. And so we would say that therefore, as our molar mass of our gas gets larger, then the pressure should decrease. And so based on what we're given for flask A We have a pressure equal to X 80 M. And then for flask B We have a pressure equal 2.5 times x 80 m. And so with this understanding, we see that flask B is exactly half of flask A. For the mass of Class A and B. We have the same mass being too gramps. But note that because flask B is half that of flask A as far as its pressure. And we understand that as molar mass increases, pressure will decrease. That means that flask B has a lower pressure than flask A. And so we would say that therefore based on our observation, the molar mass of flask B should be the larger one. So it would be 40 g per mole, which again is our higher molar mass. And therefore that means that the Mueller mask A flask A should equal g per mole. Since it would therefore have the higher pressure than flask B. And a smaller molar mass. And so for our final answers, we have our molar masses of flasks A and B highlighted in yellow. And this corresponds to choice be in the multiple choice as the correct answer. So I hope this made sense. And let us know if you have any questions