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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: blindsided on October 23, 2007, 08:14:17 PM

Title: word problem
Post by: blindsided on October 23, 2007, 08:14:17 PM

The density of liquid octane, C8H18, is 0.7025 g/mL. If 1.00 mL of liquid octane is vaporized at 100 degree C and 725 torr, what volume does the vapor occupy?

I don't really know how to set it up. I have:

.7025g/ml = 725torr(114)/Rt ( which i don't really know what it is.. is it .0821?) I keep getting the wrong answer so i think i have something set up wrong.

Title: Re: word problem
Post by: LQ43 on October 23, 2007, 08:51:10 PM

PV=nRT

you are looking for volume, you have P (remember it has to be in atm)
R = constant, T is temp (in K)

you don't have n which is moles but you have a density  0.7025 g/mL.
If you use 1.00 mL of the octane, how many grams of the octane are you using? how many moles?

you should now have P, n, R and T, find V

Title: Re: word problem
Post by: blindsided on October 27, 2007, 05:39:13 PM

So I can never use torr or hgmm? I also have to convert to atmosphere?

Title: Re: word problem
Post by: Yggdrasil on October 27, 2007, 06:22:44 PM

The units you use for pressure and volume depend on the form of the gas constant (R) that you are using.  If you wish to use torr or mmHg then you can look up the appropriate gas constant.  For values of the gas constant in different units see:

http://en.wikipedia.org/wiki/Gas_constant