Sciencemadness Discussion Board

KOH

ChemistryForever - 26-12-2018 at 04:48

Why cannot i find any KOH over 90% ?

Sulaiman - 26-12-2018 at 05:16

Potassium hydroxide is difficult = expensive to totally de-hydrate,
and very hygroscopic, so difficult to keep dry,
most of the 10% is water, with maybe up to 1% carbonate.
https://en.wikipedia.org/wiki/Potassium_hydroxide

My potassium hydroxide is supposed to be 97% ;)
but it is no more useful than 90% KOH :(
as the actual concentration of 90% or 97% is unknown,
solutions of either will need titration if accuracy is required,
so go for the much cheaper 90% KOH.

[Edited on 26-12-2018 by Sulaiman]

AJKOER - 26-12-2018 at 05:17

Quote: Originally posted by AJKOER  
.....

At the expense of a piece of glassware (attacked), I learned that a slurry of Ag2O will react with NaCl (or KCl) forming a white precipitate of AgCl and aqueous NaOH (or correspondingly, KOH). Likely reactions:

Ag2O + H2O = 2 AgOH

AgOH + KCl = AgCl(s) + KOH

Treating cold dilute KOH with Cl2 forms KCl and KClO, as noted above.

If one adds Ag2O/AgOH, to NaClO, the reported product is AgCl precipitate and AgClO3. In other words, the silver hypochlorite disproportionates to the insoluble chloride and chlorate.

[Edited on 8-8-2017 by AJKOER]


So apparently, 2 KCl + Ag2O + H2O leads to 2 KOH and insoluble 2 AgCl (which can be recycled)!

[Edited on 26-12-2018 by AJKOER]

Sulaiman - 26-12-2018 at 05:32

Quote: Originally posted by AJKOER  

So apparently, 2 KCl + Ag2O + H2O leads to 2 KOH and insoluble 2 AgCl (which can be recycled)!


So how do you economically or practically recycle AgCl to Ag2O ?

AJKOER - 26-12-2018 at 05:32

Recylcing AgCl, per my recollection, requires the right choice of sugar and strong heating (use a microwave to heat the aqueous mix which undergoes a sudden rapid change in solution color when the reaction kicks in ).

More details on the process are discussed on the web.

[Edited on 26-12-2018 by AJKOER]

Sulaiman - 26-12-2018 at 05:56

Quote: Originally posted by AJKOER  
Recylcing AgCl, per my recollection, requires the right choice of sugar and strong heating (use a microwave to heat the aqueous mix which undergoes a sudden rapid change in solution color when the reaction kicks in ).

More details on the process are discussed on the web.


Reducing sugars can convert Ag2O to metalic Ag

AFAIK LYE is used to convert AgCl to Ag2O
so I suppose it is a possible route from NaOH to KOH

The Karo syrup process uses NaOH and reducing sugar to convert AgCl to Ag in a one-pot reaction,
which is what I guess you were thinking of ?

Given the small cost difference between NaOH and KOH I do not think that your proposed route is practicable,
especially for someone who does not know why KOH is commonly 90%

P.S I'm surprised that you did not go for the +hv (sunlight) route direct to Ag :D

[Edited on 26-12-2018 by Sulaiman]

Ubya - 26-12-2018 at 10:44

Quote: Originally posted by Sulaiman  
Quote: Originally posted by AJKOER  

So apparently, 2 KCl + Ag2O + H2O leads to 2 KOH and insoluble 2 AgCl (which can be recycled)!


So how do you economically or practically recycle AgCl to Ag2O ?


plus now we need SILVER AND KCl to get just KOH, to get 100g of KOH with this method i would need: 50-100$ of silver to do all in 1 batch or 1 o 2$ of silver and waste a month of lab time doing 100 batches.

would be easier to collect wood ash from various sources, leach off the potassium carbonate with water and add calcium hydroxide, after filtering calcium carbonate you would have a probably impure KOH solution to dry. still better than using silver

ChemistryForever - 31-12-2018 at 09:47

So basically there is no impurity in it except for water and maybe some potassium carbonate trace.

happyfooddance - 31-12-2018 at 10:59

Quote: Originally posted by ChemistryForever  
So basically there is no impurity in it except for water and maybe some potassium carbonate trace.


There is definitely going to be some potassium carbonate trace. But yes, high purity KOH is usually no more than 90% KOH.

Sulaiman - 31-12-2018 at 11:24

Most 'professional' chemical supplies have a production batch number,
and each batch has a Certificate of Analysis (CoA) that is either supplied or available to customers.

Most of the chemicals that I buy do not have a CoA,
so I look for something similar.
e.g. https://www.google.com/search?q=potassium+hydroxide+CoA&...
and I assume that my sample will have similar, but not identical, impurities.
Not perfect but a good start.

While searching for a CoA it is a good idea to download an MSDS

vmelkon - 1-1-2019 at 10:08

I'm not sure why people are recommending using Ag2O. It is an insoluble oxide and also required other chemicals to produce it.
People most likely have metallic silver. They would need HNO3 to make AgNO3. They would need some soluble hydroxide to make AgOH then heat it to Ag2O. THAT IS NUTS!

Most likely people have KCl. It is best to go down the electrolysis route using the right equipment.
I used a flower pot, a polyethylene pot, some mineral oil to act as a barrier to prevent CO2 from coming into contact with the solution.

I did it with NaCl.
https://www.youtube.com/watch?v=bvNx65KXqcU
I ended up with a 1.38 M NaOH solution.
I used it to make Ca(OH)2 (solid) and I used some of the NaOH(aq) to make soap.

I considered drying it down but it is too messy and you need to use stainless steel or something. Don't use glass since NaOH attacks glass.

Another way would be the Ca(OH)2 route but that would make a very dilute NaOH or KOH solution.

[Edited on 1-1-2019 by vmelkon]

Mr. Rogers - 1-1-2019 at 10:14

Can you dry it in an oven? Never tried that with KOH.

[Edited on 1-1-2019 by Mr. Rogers]

happyfooddance - 1-1-2019 at 12:13

Quote: Originally posted by vmelkon  
I'm not sure why people are recommending using Ag2O.


I'm pretty sure it is just AJKOER who is suggesting it. He often suggests highly novel and highly impractical things but you just have to take it for what it is.

Everybody, meet AJKOER.

Sulaiman has already met him as he said:
Quote: Originally posted by Sulaiman  

P.S I'm surprised that you did not go for the +hv (sunlight) route direct to Ag :D


I chuckled as I read this because I too was expecting to see some photons in his equations as soon as I saw Ag...

AJKOER - 3-1-2019 at 05:00

OK, a few comments.

I did not dream of the Ag2O route as a path to conc NaOH or KOH (and relatively pure product as well), I accidentally observed it when it ate my glassware (so more like a real nightmare) and reported it on SM (see comments and links at http://www.sciencemadness.org/talk/viewthread.php?tid=69061#... )!

Second, depending on how cheaply one can recycle silver, it well could be an economical path as well. I have not tried adding cheap ammonia water (with total moles of ammonia at least twice that of silver chloride) to AgCl together with stirring and definitely with UV light treatment (optional H2O2 also) in a closed system. But, I suspect it may work as the complex [Ag(NH3)2(H2O)4]+ is reportedly photo sensitive likely due to its breakdown to Ag2O (which converts to a cubic Ag@Ag2O photocatalyst, see https://pubs.rsc.org/en/content/articlelanding/2012/jm/c2jm3...) and free NH3, as the reaction below is cited as reversible:

Ag2O(s) + 4NH3 + 4H2O <--> 2 [Ag(NH3)2]OH + 3 H2O (see http://www.sciencemadness.org/talk/viewthread.php?tid=70098#... )

where the removal of [Ag(NH3)2(H2O)4]+ means, to re-established the Ksp equilibrium for AgCl in the presence of ammonia, more silver chloride should dissolve.

Comments on the web are favorable with respect to concentrated ammonia solutions (see https://www.google.com/search?source=hp&ei=tQsuXJQBzZvmA... ) so high strength commercial ammonia is an option.

Don't like working with ammonia and don't have any Ca(OH)2 (including from NH3 (aq) acting on CaCl2), suspect much harder (but interesting) would be try applying strong sunlight light and reflected light from a lake or ocean or even snow (which has elevated UV levels) to a mix of AgCl/H2O2/HCO3- to benefit from the powerful photocatalytic properties of Ag2CO3 and also Ag2O/Ag (which lead to active electron holes....and eventually AgOH creating Ag2O).

Link to photocatalytic comments and warning on explosion hazard of silver and ammonia solutions at http://www.sciencemadness.org/talk/viewthread.php?tid=70098#... .

[Edited on 3-1-2019 by AJKOER]

happyfooddance - 3-1-2019 at 07:14

Silver salts costs about $1 a gram.

My KOH comes in 2 lb containers from duda diesel, costs $6.95.

Putting KOH at about $0.007 a gram.

AJKOER, no one's arguing it won't work, but everyone will argue it is nothing close to economical. Even the metathesis ways are far more practical.

AJKOER - 3-1-2019 at 07:54

Quote: Originally posted by happyfooddance  
Silver salts costs about $1 a gram.

My KOH comes in 2 lb containers from duda diesel, costs $6.95.

Putting KOH at about $0.007 a gram.

AJKOER, no one's arguing it won't work, but everyone will argue it is nothing close to economical. Even the metathesis ways are far more practical.


Wow! Ship two pounds for free(?)!

Made at home cost of recycled Silver, the cost of aqueous ammonia employed.

The price of KCl, the major cost factor depending on purity.

Ways of obtaining relatively low cost, high purity (using food grade KCl in the Ag2O path) and concentrated KOH, other than the Silver oxide path, is......(I am still waiting :o ).

[Edited on 3-1-2019 by AJKOER]

happyfooddance - 3-1-2019 at 08:47

Quote: Originally posted by AJKOER  

Wow! Ship two pounds for free(?)!

Made at home cost of recycled Silver, the cost of aqueous ammonia employed.

The price of KCl, the major cost factor depending on purity.

Ways of obtaining relatively low cost, high purity (using food grade KCl in the Ag2O path) and concentrated KOH, other than the Silver oxide path, is......(I am still waiting :o ).

[Edited on 3-1-2019 by AJKOER]


This is why you are precisely off the rocker:

I work in the food industry and can tell you with much certainty that food-grade KCl is more expensive than food-grade KOH. Pretty much ends your argument.

No, they don't ship for free, but I got 10lbs CaCO3, a liter of phosphoric acid, 2lbs NaOH and 2lbs NaNO2 and the whole lot shipped for $14 via fedex.

clearly_not_atara - 3-1-2019 at 12:45

OP is interested in drying his KOH, not making it.

I think you might be able to dry it by heating to red heat in a graphite crucible, and cooling in a sealed container purged with nitrogen. This chart says graphite is "completely resistant" to molten potash, which is what you need:

https://ddenginc.com/gaskets/spiral-wound-gaskets/graphite-f...

Remember to wear good safety goggles whenever handling dry KOH. Even a tiny amount of dust could permanently damage your vision.

But first, you should check whether this is actually necessary. Dry-enough KOH is widely used in practical chemistry.

[Edited on 3-1-2019 by clearly_not_atara]

fusso - 3-1-2019 at 12:52

Quote: Originally posted by happyfooddance  
I work in the food industry and can tell you with much certainty that food-grade KCl is more expensive than food-grade KOH. Pretty much ends your argument.
But why?

AJKOER - 3-1-2019 at 13:56

OK, to be clear my Ag2O path works with any available K salt!

And yes, the very available (and pure) may be more expensive without adjusting for shipping cost.

[Edited on 3-1-2019 by AJKOER]

happyfooddance - 3-1-2019 at 15:05

Quote: Originally posted by fusso  
Quote: Originally posted by happyfooddance  
I work in the food industry and can tell you with much certainty that food-grade KCl is more expensive than food-grade KOH. Pretty much ends your argument.
But why?


Maybe because there is a larger market (hence larger supply line) for KOH. Or maybe because with KCl you can make KOH and chlorine.

AJKOER - 5-1-2019 at 05:49

One may be able to obtain 99.1% KCl in 40 pound bags as a water softener in select Home Depots for $32 (https://www.homedepot.com/p/Diamond-Crystal-40-lb-Potassium-... ).

Apparently, due to the use of KCl as a path to KClO3, in person and credit card purchases only (basically, you just put yourself on a watch list!).

[Edited on 5-1-2019 by AJKOER]

Tsjerk - 5-2-2019 at 07:02

For the reason mentioned in the attachment the silver method suggested by AJKOER doesn't work. In alkaline solutions Ag2O is less soluble than AgCl. It actually works the other way around, AgCl and hydroxide form Ag2O.

Attachment: willbanks1953.pdf (706kB)
This file has been downloaded 347 times

AJKOER - 5-2-2019 at 08:32

Quote: Originally posted by Tsjerk  
For the reason mentioned in the attachment the silver method suggested by AJKOER doesn't work. In alkaline solutions Ag2O is less soluble than AgCl. It actually works the other way around, AgCl and hydroxide form Ag2O.


Having worked with Silver salts and performed a successful recovery of Ag2O, the alluded to paper is correct on careful reading. On page 1, there is a comment on boiling with NaOH for 15 minutes.

So, the reaction is:

AgCl + NaOH + Heat = AgOH + NaCl

2 AgOH = Ag2O + H2O

Now, my report on strong NaOH formation on standing may actually be associated with silver acetate and not silver chloride. On a supplied old paper on the solubility of Ag2O presented on SM, it was noted that AgOH displays amphoteric behavior (see 'The Solubility of Silver Oxide in Water, in Alkali and in Alkaline Salt Solutions. The Amphoteric Character of Silver Hydroxide' by HERRICK L. JOHNSTON, et al). So, the first equation is perhaps more reversible with basic sodium acetate as opposed to aqueous sodium chloride conaining a suspension of Ag2O.
---------------------------------------------------------

As such my revised alternative path (to be verified) for KOH employing Ag2O may be possibly sourced from potassium acetate or potassium bitartrate (cream of tartar). While the latter food additive goes for around $7 a pound, it is readily available on amazon and is not on a watch list.

More interesting is simply mixing an organic potassium salt with Ag2O and arranging the aqueous suspension in a large surface area shallow dish in strong visible light! Per a reference (see https://onlinelibrary.wiley.com/doi/abs/10.1002/chem.2011010... ) on the light conversion of Ag2O to the excellent photocatalyst janus particle Ag@Ag2O, generating electrons and electrons holes, which could attack the organic anion leaving KOH.

[Edited on 6-2-2019 by AJKOER]

Herr Haber - 6-2-2019 at 04:23

Quote: Originally posted by clearly_not_atara  

I think you might be able to dry it by heating to red heat in a graphite crucible, and cooling in a sealed container purged with nitrogen. This chart says graphite is "completely resistant" to molten potash, which is what you need:

https://ddenginc.com/gaskets/spiral-wound-gaskets/graphite-f...

[Edited on 3-1-2019 by clearly_not_atara]


Wouldnt you have to use an inert atmosphere for the whole process ?
Red hot graphite crucible = lots of CO2 to react with the KOH

I also dont see how to avoid contaminating KOH with graphite. Whenever I use my kiln I always leave a good trail of carbon dust between the mold and the kiln.
(But maybe I should just use a new crucible and stop being so cheap)