00:01
Okay, so at 20 degrees, the vapor pressure of ethanol is 45 tor, and the vapor pressure of methanol is 92's tor.
00:17
And so we want to know what the vapor pressure is at 20 degrees for a solution prepared by mixing 33 grams of methanol and 56 grams of ethanol.
00:25
So what we need to do is to find the total pressure of a solution or of a mixture.
00:31
You take the mulp fraction by and multiply it by the pressure of one, or the vapor pressure.
00:38
Of one and then take the mole fraction of the other and multiply it by its vapor pressure.
00:48
So you can do e for ethanol and m from ethanol.
01:00
So we have the vapor pressures for both 45 and 92, but we need the mole fraction of each one.
01:05
So in order to find the mole fraction, we need to see how many moles altogether we have and then see how many moles of each one we have.
01:15
So we need to take the masses of each of these and convert them into moles first.
01:25
So to convert grams into moles, we use the molar mass.
01:29
So the molar mass of methanol we can look up.
01:35
The molar mass of methanol is 32 .4 grams.
01:45
And the molar mass of ethanol is 46 .7 grams.
01:57
So this gets us into moles, and so we can see how many moles we have all together.
02:01
So it'll be 33 .0 divided by 32 .04.
02:07
So this gives us 1 .03 moles.
02:12
And then for ethanol we have 56 .0 divided by 46 .07...