Tuesday
September 30, 2014

Homework Help: Distillation Lab Calculations

Posted by ~christina~ on Wednesday, September 26, 2007 at 9:30pm.

I had to do a fractional distillation while my lab partner did a simple distillation. I had 2 unknown compounds which could have been any of the following:
heptane, cyclohexane, toulene, octane,


Well I think I went and boiled the solution a little too quick b/c the liquid which was supposed to be condensing out went and started to come out of the neck of the hickman head...I went and pippeted off 3 ml total of that liquid. Unfortunately I went and pipetted of the forerun as well in the liquid which was mixed together. Out of the original 7ml only 4ml was left and then there was even less from what I could see since the liquid mix must have evaporated alot.

In the end the compound finally leveled off at 110 degrees celcius.
That meant of course that it had Toulene in it but as for the other compound I wasn't certain to the identity. I had observed that the thermometer had leveled off at 90 degrees celcius for awhile though but in my panic I went and pipetted that off as well and got that mixed into the forerun. All I got was 0.5 ml of distillate that I was sure was a certain compound since the temp had leveled off at 110o

The refractive index for the simple distillation for 2 samples, 1 taken at 1ml and 1 taken at 3.5ml was 1.415(1ml sample at 26o) and 1.4724(3.5ml sample at 26o)

For the fractional that I did I never got 1ml of distillate for what I started to keep track of so I just used a sample from my 0.5ml that I had.
I got 1.4804(26o)

I narrowed the compounds based on the refractive index to toulene & cyclohexane
____________________________________
The thing is that we were told to find out how much of each compound was in each sample unknown. They told us that they had added Decane to each sample.

I don't know how to calculate the percentage of each.
I was told that the impurity of the sample would lower the refractive index that we got for the sample.

an example of the board said this:

Toulene (60%) + ethylbenzene (30%) + Decane (10%)
RI= 1.4967 1.4932 1.4119

RI mix= 1.4967(0.60) + 1.4932(0.30) + 1.4119(0.10)

It isn't explained in my book how to calculate the percentage of each.

Help Please =)

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