00:01
Hi there.
00:02
In this question, we have a vapor or a gas, and we are trying to, first of all, determine how many moles we have.
00:09
And then once we know that, we need to calculate its molar mass.
00:14
So to determine how many moles, we see that we have a volume, we have a temperature, we have a pressure.
00:21
So that means that we can use the ideal gas law equation to determine the number of moles of this gas that we have.
00:28
So that's pv equals nrt.
00:30
If we're trying to solve for n, that means we will divide both sides by rt to isolate n.
00:38
And we see that n equals pv over rt.
00:45
Okay, so let's pull out the values from the problem.
00:49
For tor, for pressure, we have 784 tor.
00:59
The gas is going to take up the entire volume of this flask.
01:04
So let's talk about volume for a second.
01:06
When we have a 125 milliliter flask, it's usually marked with a maximum being somewhere around here.
01:17
But if we have a gas, it's going to fill up all of this space.
01:20
So we need the total volume of this flask because the gas fills to expand or expands to fill its container.
01:27
So we see that that entire volume is 152 milliliters.
01:33
We could figure that out by filling the flask all the way with water and then pouring the water into a graduated cylinder to measure it.
01:40
So we could determine the volume of this flask, but we would like to have that in liters to plug it into our pv equals nrt equation.
01:47
So i want to convert this 152 milliliters to liters by dividing by 1 ,000.
01:55
That gives me 0 .152 liters.
01:59
So volume is 0 .152 liters.
02:07
R is the universal gas constant.
02:09
I want to select the one that has tore in it.
02:12
So that one is the 62 .36 liters times tor over mole kelvin.
02:22
Notice temperature has to be in kelvin.
02:25
So that brings us to our next issue here...