00:01
So in this problem, we're given p total, i'll call it pt, as 745 millimeters of mercury.
00:10
And then we have the partial pressures of co2, ar, and o2.
00:16
And we want to find the partial pressure of the last gas in this mixture, which is helium.
00:22
And so our givens, our p, co2 is 125 millimeters of mercury, our p .a .r.
00:35
Is 214 millimeters of mercury.
00:40
Our p .o2 is 187 millimeters of mercury.
00:48
And our p -h -e, that is what we're trying to find, the partial pressure of helium.
00:54
And so p total is equal to the sum of the partial pressures of all the gases.
01:01
So p -c -o -2 plus p -a -r plus p -o -2.
01:06
Plus phe.
01:09
So if we rearrange this to solve for phe, we have p -t or p -total minus p -c -o -2, minus p -a -r, minus p -o -2.
01:25
And when we plug in these values on the left, we get that the partial pressure of helium is 219 millimeters of mercury.
01:35
And so now we want to find the...
01:40
Volume as well as the mass of this helium.
01:46
And so the way we do that is first we want to find the molar fraction of helium...