ellafuntay
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absolute beginner
Hello. I am as green as an aspiring chemist could be. Didnt do so well in high school, have a successful career as a craftsperson, but always have
been curious about chemistry.
I finally started reading everything i could find about the subject, and ive been trying to teach myself, starting on a very basic level. Like,
learning about atoms and the periodic table, and so forth.
Yesterday I took the plunge and synthesized chloroform. It seemed like an easy process and like one that I most likely would not kill myself
attempting. It seemed to go well.
I chilled the bleach and acetone in the freezer. I calculated the amounts to use based on moles, taking into account the strength of my bleach. I
ended up with 60ml of crude chloroform.
Today, I tried to distill it to clean it up. This was my first distillation ever. I had the raw CHCl3 in a round bottom flask in a water bath.
This is where things didnt go as planned. Distillate started to come through the condenser much earlier than i expected. In the mid 40s C, so i
collected it. I know the boiling point of CHCl3 is 61C, but my temperature never got that high.
I switched receiving vessels and caught the drippings from 56C and on, intending to keep up to 64C or so, because i forgot to callibrate my new
thermometer. I am at sea level in the USA.
The temp seemed to level out at 56-57C for 15 minutes, then started dropping quickly, and I about out of liquid when it was around 45C.
So, Ive UTFSE, and im not sure whats going on. The first batch(45C-55C) of distillate smells much more like chloroform than the second batch. Id
like to add some ethanol to the stuff and put it away in the dark until later, but im not sure which one is the better batch. My intuition tells me to
follow my nose, thats worked for me well in my career as a bread baker.
Can anyone explain to me what is the deal? i really have searched before posting this. Could it just be my thermometer was off? This happens in
candy making, another hobby of mine. Thanks for reading all that, I await your collective wisdom.
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HgDinis25
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Perhaps your heating was uneaven (meaning some parts of your boiling flask were hotter than others). I say this becase something clearly came out
around 56ºC (wich is close to the b.p. of chloroform, aceptable for a bad thermometer).
Add your 45ºC fraction of distillate to a beaker and start heating it slowly. Register the temperature when it starts to boil, this time using a
thermometer that you're sure is well calibrated.
You can also make a density test if you have a Volumetric Flask or a Densymeter.
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Chemosynthesis
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Additionally, your thermometer may not have been places at the correct depth for distillation, so be sure to check that carefully when distilling as
it may throw off measurements as well.
Here is a good image.
http://www.chemistry.sjsu.edu/straus/DISTILLATION%20htms/Sim...
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ellafuntay
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thank you both for the tips. chemosynthesis, i believe you may have nailed it. i had thought i had placed the thermometer properly when i put the bulb
lined up exactly with the center of the side arm. i now see that i had placed it too high. i made the mistake of relying on my memory, i should know
better by now. i need to check the thermometers accuracy also. for the record, the first batch of distillate was 36ml, the second was 16ml. do
chemists say "heads and tails" for the fractions ever , like whiskey makers do?
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Chemosynthesis
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Glad we could help.
I have never seen this in publication, but I used to call the distillate fractions outside of my BP range by those terms in the lab. I'm not sure if
this is because I mostly work with alcoholics in a more biological capacity now (surprisingly excellent scientists in this case), but in publication
the general phrasing as "first XmL distillate was discarded" or unmentioned ("fraction boiling between temp1-temp2 was collected, consisting of XmL")
is more in line with what I recall.
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Metacelsus
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http://eweb.chemeng.ed.ac.uk/jack/newWork/Chemeng/azeotrope/...
If you had 3% or more water in your chloroform, the boiling point of the mixture would have been reduced to 56.3 C. Did you dry the chloroform first?
If not, this probably explains it.
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ellafuntay
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aha!no, i didnt dry it first. i had seen some mention of that, but i figured id get rid of the water when i distilled it. now i understand, those
pesky azeotropes! So, is it normal for the temp to drop after the last substance to boil comes over? i mean, if there is nothing to boil, obviously.
but the water would have been left in the RBF after the chloroform went over, no? Ill dry it next time. Ive been using MgSO4 to dry everything so
far(ethanol, acetone, and next time, chloroform). Ive read online that after drying the epsom salts in the oven, one should grind up the lumps before
adding to the liquid, but ive also read to not do that. what do you guys say?
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Chemosynthesis
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Good catch on the azeotrope. I didn't consider the bleach dilution.
I prefer powdered drying agents since speed of drying is correlated to exposed surface area, which forms a hydration shell. If you are not using a
dessicant with a color indicator, you can see the powder stop clumping when you swirl the flask. This indicates it is no longer absorbing water, so
stop adding since all you are doing now is physically retaining some solvent when decanted/filtered.
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ellafuntay
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In the bakery, we try, whenever possible, to blame the equipment for our mistakes. However, I want to get off to a moral start in chemistry, so I must
report that i checked the thermometer today and it was exactly 100C in boiling water. Darn!
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chemrox
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I came back to 'wet chemistry' after a 20+ year hiatus. I found myself goofing up all over the place. I couldn't believe how flaky I had become. Guess
what I did to start recovering lab skills? (Besides washing glass?). Distillations, distillations, distillations. Simple, simple-vacuum,
simple-fractional, vacuum-fractional, high-vacuum, inert-atmosphere, etc. Until=>reactive-distillation!! The skills range from thermometer bulb
placement, torching the glass, proper clamping, greasing joints, water flow monitoring and control. Please don't overlook the skills a chemist should
have.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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ellafuntay
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I didnt mean to sound like i was making light of the skills a chemist should and does have. I am very intimidated by how much there is to learn, but
being old enough to remember the pre-internet days, Im really glad this resource is here.
I am happy to report that i made another batch of CHCl3, dried it over MgSO4, added it to the old batch, re-distilled it with the thermometer in
the proper location, and it came over at exactly 60C! im now the proud owner of 79mls of CHCl3, stabilized with dried everclear, in brown glass bottle
with teflon tape coated stopper. Im pretty excited, I must admit. Thank you to everyone who gave advice!
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aga
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Now that you have some chloroform, you should know how to Dispose of it safely ...
http://www.sciencemadness.org/talk/viewthread.php?tid=11632
Edit:
Congratulations on a good result !
[Edited on 12-11-2014 by aga]
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