PChem sucks.

Posted by Shork on Oct. 5, 2007, 4:14 p.m.

So anyway, I am taking physical chemistry I and it sucks. I got a 98% on the first test, but someone else got a 100%. That bastard.

Right now I need to be typing my lab report on the determination of the critical volume of Benzene gas. We had to make 4 vacuum sealed tubes of benzene, and then heat them, and measure the heights of the liquid at varying temperatures.

Then we had to make a calibration curve for volume based on height for each tube.

Then we have to use insane ass simaltaneous equations to solve for the average density of the benzene.

By the way, for tube 1 with mass m1, gas volume Vg1 and liquid volume Vl1, and tube 2 m2, Vg2, Vl2, the average density is:

d = (m2(Vl1 - Vg1) + m1(Vg2-Vl2))/2(Vl1Vg2-Vl2Vg1)

Bonus points if you can figure out how I got it.

Short blog? I've seen shorter stay on the front page.

Ok, here is some hints on getting the math:

first, remember that the tubes contain benzene gas and liquid benzene, so the total volume is the volume of the liquid plus the volume of the gas.

Now, plug in the densities of the gas and the liquid to find mass:

m = DgVg+DlVl

Now, take two tubes and set them up like the above equation:

m1 = DgVg1 + DlVl1

m2 = DgVg2 + DlVl2

Now use simaltaneous equations to solve for Dg in terms of the masses and volumes:

Dg = (Vl1m2 - Vl2m1)/(Vl1Vg2 - Vl2Vg1)

Plug this into one of the above equations and solve for Dl:

Dl = (Vg2m1 - Vg1m2)/(Vl1Vg2 - Vl2Vg1)

Now average density is (Dg+Dl)/2.

Wasn't that easier than you r thought it'd be?

Now to get some more content for safety sake:

Last week I saw Rozen Maiden. It needed more desu.

Watch this for the lulz.

EDIT: I just finished the data work up. I have a 51% error! YES!

Comments

Shork 17 years, 1 month ago

I have no idea what you're meaning there Rob. All I know is that I weighed a piece of clean filter paper, added crystals of benzoic acid, weighed it again, and it was less. I know I added stuff to the paper, I could see it, but it apparently had negative mass.