boonga
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Potassium Carbonate aquisition?
Hey Guys,
was looking for the easiest (or perhaps slightly complicated) method of synthesizing K2C03?
I have access to a few reagents such as NaOH, HCL, NaHC03, Na2C03, KOH, H2S04, Ca(OH)2, and a few others. (listed a bunch of reagents to give a
variety of reactions i guess?)
A few equations, a procedure and method of extraction (as powder) would be much appreciated!
Thanks in advance  ,
Fire away!!
Boonga
[Edited on 12-9-2011 by boonga]
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hissingnoise
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Treating a KOH solution with CO<sub>2</sub> or with carbonic acid and evaporating would seem the simplest route . . .
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theflickkk
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I'm guessing you meant KOH, not K(OH)2?
HCl + NaHCO3 --> NaCl + CO2 + H2O
or
H2SO4 + 2NaHCO3 --> Na2SO4 + 2CO2 + 2H2O
Bubble CO2 produced through a solution of KOH
CO2 + KOH --> KHCO3
KHCO3 + KOH --> K2CO3 + H2O
Drying of the solution should give you K2CO3
Since it's deliquescent, a desiccator bag should be necessary
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bbartlog
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You can also bubble air through a hot solution of KOH. Given enough time it will convert it all to K2CO3.
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smaerd
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I bought a pound of potassium carbonate at a pottery store with I'm assuming a pretty decent purity for a couple dollars.
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CrimpJiggler
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One thing I haven't learned to do yet is to deal with gases. I know how to generate CO2 gas but how to use a gas as a reactant I'm not so sure about.
I could just add an acid and an aqueous carbonate to a flask, stopper the flask using a tubed stopper then submerge the other end of the tube in the
aqueous contents of my reaction flask. Have I got the right idea?
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Chordate
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If you're trying to make it for fun, then good on you.
If you just want it for something else, just go buy it off amazon. Not even kidding. 12 bucks for a pound.
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hissingnoise
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| Quote: | | I could just add an acid and an aqueous carbonate to a flask, stopper the flask using a tubed stopper then submerge the other end of the tube in the
aqueous contents of my reaction flask. |
CO<sub>2</sub> is very soluble in basic solution so I'd insert a second flask in-line to deal with possible suckback . . .
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boonga
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If i were to possess potassium sulfate (K2S04) what would be the easiest way too convert that to potassium carbonate using the above
chemicals/household ingredients (excluding potassium hydroxide)? That includes extracting it from solution.
cheers
[Edited on 19-9-2011 by boonga]
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Octavian
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It's been several years since I've really lurked the forums (probably since the days of Rogue and Hive  ) so I'm not sure on the current stand point of necro-posting but having Used The
Fucking Google Search Engine Because The Site One Is Shit for quite some time I never found someone report their results on the rather straight
forward sounding approach of: 2 KHCO3 -- heat --> K2CO3 + H20 + CO2.
I have had a hell of a time finding Potassium Carbonate anywhere in the country aside from one or two listings that were not only pretty damn
expensive but also wanted my left testicle to post the stuff to me. I have a few times in the past made NaCO3 from NaHCO3 by just baking it in the
oven (from memory around the 200C mark for 1.5 - 2 hours (don't quote me, it's been a while and I don't have my notebook handy - but I often did it at
the same time as dehydrating MgSO4).
Now, Potassium Bicarbonate I can get from any brewing or wine making store but at a rather steep price! Problem is, no specific info is easily found,
hell I even checked the Merck index in the end and no joy, Some places say 100C - 120C others say 110C - 400C and neither mention even a ball park
figure for the time required. So, last week I decided "Screw it!" and just bought two 50g packs of the KHCO3 to do a couple of test runs. Here are my
notes in the hopes it may help someone else in the future having the same sourcing issue:
Equipment used:
Scales accurate to 0.01g (or better)
A 25cm (10") square glass baking dish with low walls. Line the bottom with baking paper since K2CO3 is said to react with Aluminium (sorry forgot
the source for that.
An electric kitchen oven (fan forced may be a bonus)
HDPE Bottles to store the K2CO3 in.
Stoichiometry to keep in mind:
2mols KHCO3 --> 1mol K2CO3 + H2O + CO2
KHCO3 = 100.11g/mol
K2CO3 = 138.20g/mol
H2O = 18.01g/mol
CO2 = 44.01g/mol
My 50g bag of "Wine De-Acid" weighed 51g on the scales (0.51mol) which means 35.24g K2CO3 + 4.59g H2O + 11.22g CO2 (0.255mol each) - This is the best
way I had at my disposal at the time o check how the rxn was progressing. The KHCO3 was thinly poured over the baking paper ('wax paper in the U.S?)
covering the bottom of the shallow baking dish and put into a pre-heated oven at 120C. After 30 minutes, no change in appearance was noticed, the
course powder was stirred around a little and the oven temperature taken to 175C with the fan turned on (fan forced oven), after an addition 30 min at
this temp no visual change was noticed (I expected to see a visual change due to my experience with Na's). So the temperature was raised to 200C, I
look in 2 or 3 minutes later and most of the top layer was turning brown and some specs almost black, "Shit." I think so I open the oven door, drop
the temp back to 140C - 150C and cool the baking dish a bit by sitting it on a wet towel for a minutes or so while stirring the powder around. It was
placed back into the oven. Two hours from starting, the product still looked the same apart from the brown flecks, and was weighed at 36.17g which is
0.93g more than it theoretically should so it was returned to the oven at 150C with the fan on for another 30 min (Total time now = 2.5 hours) Weight
dropped slightly to 36.02g (Still 0.78g heavier than theory. At this point it was bottled while still hot. After pouring it into a bottle I noticed
with in a few seconds the odd tiny crystal clinging to the paper I used to transfer it had began to draw enough water from the air to melt itself.
The second 50g packet of the KHCO3 (51.68g - 0.516mol) was then spread over the same baking paper, in the same baking dish, but this time I kept the
temperature to a maximum of 150C and cycled the oven fan so it was on for 30min - off for 30 min. After 2 Hours the product is still pure snow white
with no visual difference to the starting material. At 2.5 hours the oven was turned off because 3am had come around fast and it was time for bed. The
K2CO3 was weighed while it was pretty hot and dry @ 36.58g (0.93g over theory).
Notes I've taken from this:
* Don't heat KHCO3/K2CO3 mix over 175C due to discolouration.
* Possibly be able to run to completion in 2.5 hours @170C.
* K2CO3 is deliquescent (very hygroscopic) - Humidity wasn't excessive and small crystals were 'melting' themselves in seconds once cool.
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Hawkguy
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Bubble CO2 through an ALCOHOLIC solution of KOH. The Carbonate will precipitate. Don't use air since air is only like 0.4% CO2.
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aga
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Quote: Originally posted by CrimpJiggler  | | One thing I haven't learned to do yet is to deal with gases. I know how to generate CO2 gas but how to use a gas as a reactant I'm not so sure about.
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Usually you just produce an excess of the gas and whang it into the reaction chamber, dealing with the excess in some sort of scrubber arrangement.
http://www.sciencemadness.org/talk/viewthread.php?tid=61903
http://www.sciencemadness.org/talk/viewthread.php?tid=62254
In the second one i didnlt want to deal with an excess of the gas, so found a different way to do it.
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gdflp
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| Quote: Originally posted by Octavian |
Now, Potassium Bicarbonate I can get from any brewing or wine making store but at a rather steep price!
* Don't heat KHCO3/K2CO3 mix over 175C due to discolouration.
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I'm guessing that this would not happen with the pure material, and that the discoloration is due to an organic impurity charring at that temperature.
Seeing as it's expensive though, recrystallization may not be worth it.
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