Sciencemadness Discussion Board - potassium hydroxide?

potassium hydroxide?

CrossxD - 11-9-2016 at 09:14

Hello,
Is possible to make potassium hydroxide from calcium hydroxide and potassium sulphate?

Metacelsus - 11-9-2016 at 10:05

Not by precipitating calcium sulfate (if that's what you were thinking). Calcium sulfate is more soluble than calcium hydroxide.

If you had potassium carbonate, you could use that to precipitate calcium carbonate.

[Edited on 9-11-2016 by Metacelsus]

CrossxD - 11-9-2016 at 12:38

Hmm and is there way to make carbonate ftom sulphate? I cant find way :/

NEMO-Chemistry - 11-9-2016 at 14:40

Quote: Originally posted by CrossxD

Hmm and is there way to make carbonate ftom sulphate? I cant find way :/

found a patent

http://www.google.co.uk/patents/US1992324

woelen - 12-9-2016 at 00:31

Quote: Originally posted by Metacelsus

[...]Calcium sulfate is more soluble than calcium hydroxide.[...][Edited on 9-11-2016 by Metacelsus]

Is this true? As far as I know, Ca(OH)2 is moderately soluble in water, while CaSO4 is insoluble. So, I can imagine that you can make a (dilute) solution of KOH by mixing stoichiometric amounts of solutions of K2SO4 and Ca(OH)2. Both K2SO4 and Ca(OH)2, however, are only moderately soluble, so your solution will be dilute. It still will contain a little Ca(2+) and SO4(2-) ions as well and it will be hard to add solutions in exact stoichiometric amounts.

gdflp - 12-9-2016 at 05:19

Quote: Originally posted by woelen

Surprising as it is, it is indeed accurate. Ca(OH)<sub>2 </sub> has a solubility of about 1.85g/L at STP, whereas CaSO₄ has a solubility of slightly over 2g/L according to my CRC. Interestingly, Ca(OH)₂ has a reverse solubility curve, as the solubility is well under 1g/L @ 100°C

CrossxD - 15-9-2016 at 05:57

and how about electrochemical way? is possible to make stoichiometric amount of potassium hydroxide and chlorine? If is than how?

Scalebar - 15-9-2016 at 07:01

Chloralkali process basically, only with KCl instead of NaCl. You just need to keep your electrodes in separate compartments - two beakers, connected by a strip of wet paper, electrode in each.

ficolas - 15-9-2016 at 07:04

Electrochemically it is possible from KCl, and KCl is sold as sodium free salt in lots of supermarkets.

Read about the chloralkali process, there is a ton of documentation about in this forum, and even more in the rest of the internet.

The problem it has is that for chlorine free KOH you need mercury and that will produce mercury contaminated KOH

If you can find Ca(OH)2, and K2CO3, its easier that way. Or a very impure and small amount og both KOH and NaOH can be obtained from ashes.

I wanted to try decomposing a calcium carbonate from marble into calcium oxide to get calcium hydroxide, but my "tech" level is still too low for this. (A bit less than 900 degrees are needed) Its is the way of getting CaOH I know, other than buying it

AJKOER - 15-9-2016 at 11:33

Here is a curious path assuming you are willing to may a silver investment:

Quote: Originally posted by AJKOER

I have been experimenting with Silver salts recently, and I believe I have accidentally demonstrated that one can create a strong base from Ag2O!

Per Wikipedia (http://en.m.wikipedia.org/wiki/Silver_hydroxide#Preparation ):

"It will also react with solutions of alkali chlorides to precipitate silver chloride, leaving a solution of the corresponding alkali hydroxide.[12][11]"

I prepared some Ag2O, which left in the presence of NaCl and some water, then appears to have reacted as follows:

Ag2O + H2O + 2 NaCl --) 2 NaOH + 2 AgCl (s)

Interestingly, as one can recycle the Silver chloride, it appears that one can create a large amount (by recycling the Silver chloride) of NaOH (or KOH..) from the likes of inexpensive NaCl (KCl..).

Cool!

The attached picture shows one etched storage jar (I would not recommend repeating this experiment with your expensive glassware!).

[Edited on 4-4-2015 by AJKOER]

Link to threads picture: https://www.sciencemadness.org/whisper/post.php?action=reply...

Reactions:

Ag(+) + OH- = AgOH

2 AgOH = Ag2O + H2O. (See https://en.m.wikipedia.org/wiki/Silver_oxide )

2 KCl + Ag2O + H2O = 2 AgCl(s) + 2 KOH

Note, the last reaction consumes water in the process of forming the hydroxide. My Silver salt was Silver acetate which one can prepare by mixing Silver metal, vinegar and dilute H2O2 together with a very small amount of say KNO3 (acting as an electrolyte as the underlying process is electrochemical in nature). Jump start the reaction in a microwave and periodically add more vinegar and H2O2. Silver acetate is soluble in acetic acid to which one can add a convenient alkaline to prepare AgOH/Ag2O.

[Edited on 15-9-2016 by AJKOER]

CrossxD - 16-9-2016 at 01:38

Awesome process, but how should I recycle silver?

CrossxD - 16-9-2016 at 06:18

And how about use calcium acetate, react it with potassium sulphate, than filtrate calcium sulphate.
There should left potassium acetate wich I can thermaly decompose to potassium carbonate and from carbonate I can make hydroxide

AJKOER - 17-9-2016 at 05:46

There are a few methods to recycle AgCl. A few years ago, my recollection was boiling AgCl with NaOH in a microwave which eventually changes color to Ag2O. Then, I beileve I used as a sugar glucose source (which acts as a reducer) some molasses.

Here is a link to another method by dissolving the AgCl in conc ammonia and then employing ascorbic acid as the reducer: https://www.google.com/url?sa=t&source=web&rct=j&...

An interesting exercise that I would recommend performing at least once.

[Edited on 17-9-2016 by AJKOER]