Here it states in this example question, an unknown gas with a mass of 0.1727 grams is placed into 125 milliliter flask if its pressure is 0.833 atmospheres at 20�C. What is the identity of the gas here? We're given different gases and we need to realize here that they're giving us our grams, which is Massachusetts. They're giving us volume, they're giving us pressure, and they're giving us temperature.
With this, we'll be able to find the molar mass of our unknown gas, and then all we have to do is see which one has that molar mass as their actual weight. So we're going to say here molar mass equals RTPV. We're going to plug in the mass of our unknown. We're going to plug in R, which is 0.08206 liters times atmospheres over moles times K. Remember, temperature has to be in Kelvin, so add 273.15 to this number to give us 293.15 K divided by our pressure, which is 0.833 atmospheres and then our volume.
We convert those milliliters into liters, so that gives us 0.125 liters. Here we look and see what units cancel out and we see all that's left is grams over moles, so we have molar mass. When you plug that in, you get approximately 39.90g per mole. All we have to do now is see which one of these gases has a molar mass closest to our answer.
So here N2, the two nitrogens, comes out to 28.02 grams per mole. Argon, from the periodic table, is approximately 39.95 grams per mole. Oxygen is 32g per mole. Neon is approximately 20 or so grams per mole according to the periodic table. And then chapter 4 is roughly around 16g per mole. Our closest answer would have to be argon. It's the one that's closest to this 39.90g per mole.
So here we've just utilized the molar mass version of the ideal gas law to find the molar mass of our unknown gas.