Suppose you are given two 1-L flasks and told that one contains a gas of molar mass 30 and the other a gas of molar mass 60, both at the same temperature. The pressure in flask A is x atm, and the mass of gas in the flask is 1.2 g. The pressure in flask B is 0.5x atm, and the mass of gas in that flask is 1.2 g. Which flask contains the gas of molar mass 30, and which contains the gas of molar mass 60?

Video transcript

hi everyone for this problem we're told to consider two flasks with a volume of one leader With one flask having a gas with a molar mass of 20 g per mole. And the other flask containing a gas with a molar mass of 40 g per mole at 25 degrees Celsius. The gas in the gas sample and flask A has a pressure of X 80 M. And a mass of two g at the same temperature. The gas sample in flask B has a pressure of 0. X 80 M. And a mass of two g. We need to identify which flask corresponds to the given molar mass is 20 g per mole and 40 g per mole. Okay, so we're dealing with gasses here and we have two flasks. So we need to we need to think about our ideal gas law here, which tells us that pressure times volume is equal to N. R. T. Okay. And the problem tells us that we're at constant volume and temperature. Okay, so at constant volume and temperature, our pressure is going to be directly proportional to N. Which is our number of moles. And they tell us that we have two g. So we have an uh equal amount of grams. two for each one. Okay, so because our pressure and our N. Is directly proportional, we can see that a decrease in molar mass is going to lead to an increase and N. And P. Okay, so if we have a decrease in our molar mass that's going to increase our number of moles and our pressure. So that means flask A. is going to equal R 20g per mole, and flask B is going to equal Our 40 g per mole. So this is going to tell us given the molar masses. This is how we're able to identify which flask can corresponds to the given molar masses. That's the end of this problem. I hope this was helpful.