Chemgineer - 17-8-2023 at 14:31
When carrying out fractional distillation I keep having a suspicion that my thermometers are reading low. For example I am currently condensing ethyl
acetate at a reading of 70 deg C on both a proper thermometer and also a digital one.
Is this likely some thermal effect and my glassware is just radiating some of the heat?
Sorry for the daft question.
j_sum1 - 17-8-2023 at 15:08
What is your altitude?
I am nearly 900m asl here and it is enough to make a difference. (But I also have issues with inaccurate thermometers.)
Chemgineer - 17-8-2023 at 15:19
I do live on a hill, maybe 100 foot above see level, didn't consider that.
Rainwater - 17-8-2023 at 17:11
Ive had trouble calibrating different thermometers. Bottom line, you get what you pay for.
I use a series of boiling test to form a calibration curve for precision thermocouples.
It really depends on where you want your accuracy to be. A few referance points below and above your target can get you within +/- 0.1 very cheap and
easily.
https://www.engineeringtoolbox.com/boiling-points-fluids-gas...
This link has a good list and there are plenty of easy to obtain compounds
−78.5c dry ice acetone
−42.25c liquid propane. (Can be condenced using the dry ice bath)
0c Ice water
56.08c acetone
64.7c methanol
78.2c azeotropic ethanol
80.3 Isopropyl Alcohol
100c water
108.7c saturated sodium chloride solution
160c Turpentine
197c Ethylene Glycol
Chemgineer - 18-8-2023 at 11:24
Hmm actually maybe I have another suggestion, what I was trying to do is separate ethyl acetate from isopropyl alcohol via a fractional distillation.
I've just realised they form an azeotrope though, that might be why I was getting the lower boiling point.
I think this combination would boil at 75.3 deg C and my final product will be 75% ethyl acetate and remaining isoproyl alcohol.
[Edited on 18-8-2023 by Chemgineer]
Rainwater - 18-8-2023 at 15:25
Looks like your in for trouble
70.4c ethyl acetate + water @ 91.9% [1]
80.4c IPA + water @ 87.7[2]
75.3c IPA + ethyl acetate @ 75% [1]
Might be easier to reduce everything back to C, H2, and O2 then start over
Perhaps an excess water will remove most of the ethyl acetate? But thats a wild guess
[1]wiki link
[2]https://doi.org/10.1016/j.seppur.2005.07.025
[Edited on 19-8-2023 by Rainwater]
Grizli7 - 17-12-2023 at 04:58
Remember that all thermometers like any measuring device have their own error and division into accuracy classes. If you fundamentally need accuracy,
it is better to give the thermometer to the pale laboratory and in the future take into account the error in work.
I do not know what thermometer you have, but if it is a mercury device for ordinary accuracy, its error is + -1 degrees Celsius.