I preformed my first ever chemistry experiment last night. It was the first experiment in The Illustrated Guide to Home Chemistry by Robert Bruce
Thompson, Differential Solubility: Separate Sand and Sucrose.
I substituted regular sugar for sucrose. I followed the instructions to a T, and was able to successfully separate the sand from the sugar. Then I
began the process of recrystallizing the sugar.
Everything was going fine, and the water was evaporating at a decent rate, so I just sat back, watching and waiting. As the water got down to about 50
ml, I could see crystals starting to form on the bottom of my beaker.
Then when the water level got down below ~25 ml, the water began to turn a golden color. At this point I hadn't realized that I was beginning to make
caramel...but as the water began to completely evaporate, it became apparent. I attempted to stir it with a glass stir rod, and as soon as the sticky
substance hit the colder air on my stir rod, it hardened on the rod like hard candy (which is exactly what it was).
I thought I'd ruined my beaker, but all it took to get the hard caramel off was to heat it full of water on my hot plate. It solved (is that the
proper verb?) in the water and dumped right out.
I'm actually glad that it didn't work out. I thought this was going to be a super simple experiment and I'd just be doing it to check it off the list.
Now I have something to figure out.
So, how do I recrystallize sugar without it caramelizing? Do I need to do a slow evaporating without the heat? Or maybe just turn the heat down a bit
when most of the water is gone?
I'm completely new to chemistry, so if you all think it would be better for me to figure this out on my own, I'm ok with that. I am taking a class
this coming up semester, but for now you all are my teachers. paulll - 22-11-2020 at 12:02
Couple of things you might do in that scenario. Keeping that temp under control is thing one. I'd personally transfer it to something,"flatter," than
a beaker - dish, plate, bowl, anything to get the surface area up. And don't underestimate the power of pointing a desk fan at it.mackolol - 22-11-2020 at 12:04
Just buy yourself crystallising dish, pour the solution there and wait till all the stuff evaporates. Crystallising dishes are very wide but short,
which provides big surface of evaporation compared to volume of your solution.
You will get very big and beautiful crystals, because the solvent (in your case water) evaporation will be slow.
However if you want to get rid of the solvent faster, you can direct fan airflow on the surface and if this doesn't satisfy you either, apply gentle
heat, if the heat is strong, then just remove it when crystals start to appear.
[Edited on 22-11-2020 by mackolol]Fyndium - 22-11-2020 at 12:30
I use platters to evaporate and dry stuff. A fan is most helpful. I have placed a small styrofoam box (thanks chinese glass suppliers) filled with
warm, hot or almost boiling hot water beneath the platter to warm it up.
Coarse crystals, usually after suction filterings I have placed over fine steel mesh and blown air from below. The damp crystals were free flowing dry
within 15 minutes.
Sugar needs to be evaporated with lower temp than it's decomposition. It's a classic example of such compound. Similar to it, ammonium formate will
make syrupy formamide if heated too much, so just simmering off the water is a must. Another option to fasten this process by a magnitude is to vacuum
distill off the water.
[Edited on 22-11-2020 by Fyndium]MycoTricho - 22-11-2020 at 12:40
I was going through the Homemade and Repurposed Lab Gear thread, and found this recommendation for repurposing candle glass for crystallizing dishes. Do you think this one will work?
Edit: Not sure why the file got turned sideways. That happened on another BB Code based forum I am on as well.
[Edited on 11/22/2020 by MycoTricho]unionised - 22-11-2020 at 12:45
One simple way to avoid overheating was established some time ago.
Heat the material on a steam bath.
Sugar needs to be evaporated with lower temp than it's decomposition...
I wonder if Robert Bruce Thompson left this information out intentionally to help to learn a lesson. He did say something like "try not to scorch the
crystals" but there was a lack of any actual information on temperature and such.DraconicAcid - 22-11-2020 at 12:51
Even if you didn't get nice crystals of sugar, you did successfully separate them.MycoTricho - 22-11-2020 at 13:00
Even if you didn't get nice crystals of sugar, you did successfully separate them.
Absolutely. And according to my scale, which may not be 100% accurate but close enough, I ended with the same amount of sand that I started with, 10
g.
I do feel like I should get this down, though, before I move onto the next one I am going to attempt, purifying copper sulfate. That also includes a
crystallization step. That is the third experiment. I'm skipping the second one, purifying ethanol, because I don't have a distillation setup.MycoTricho - 22-11-2020 at 13:06
