We have a lab assignment that we haven't had a lecture on yet. It's the Pv=nRT. I had to graph 50 plus atm measurements & K temps on Excel. We are supposed to answer "# of moles of the gas in the 250mL sealed flask." I do not know where to go next?

1 Answer

So, #PV=nRT# is the Ideal Gas Law where "P" is the pressure (in the question it should state it. Maybe it says "at STP" or SATP" or just use each pressure measurement). "V" is the volume in litres , "n" is the number of moles, "R" is the constant 0.082 atmL/moleK, and "T" is the temperature in Kelvin .

Let's assume you're answering the question for SATP . First, the pressure (P) at SATP is 101.325 kPa or 1 atm , and the temperature (T) is 298.15 K . Sub these into the equation as follows:

P = 101.325k --> 1atm
V = 250ml --> 250/1000 --> 0.25L
R = 0.082 atmL/moleK
T = 298.15K

#(1atm)(0.25L)=n(0.082 (atm*L)/(mol*K))(298.15K)#

Now, do the inverse operation of multiplication (division) to isolate "n". Divide by #(0.082 (atm*L)/(mol*K))(298.15)# on both sides like so:

#((1atm)(0.25L))/((0.082 (atm*L)/(mol*K))(298.15K)) = n#

Cancel any units necessary, and you should end up with:

#n=0.01# (approximately) --> Therefore there are 0.01 mols of gas in the flask.

Since this was just an example, just sub in whatever temperatures and pressures you were given and solve! Hopefully this is what you were asking and hopefully you've understood all this! :)