Talk:Potassium hydroxide

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Inconsistency with NaOH[edit]

Both this page and the NaOH say their compound is more commonly used for biodiesel because it does not clump as much. They can't both be right.

A general comparison of differences in properties between KOH and NaOH may be of interest too. Perhaps just after the current text that mentions that generally they are very similar. —DIV (138.194.12.32 (talk) 05:59, 25 September 2009 (UTC))

Melting Point[edit]

A wider search of the net shows some variety of figures for the melting point of KOH. ONe manufacturer quotes 360C, and another source quotes 380C. The Wikipedia article quotes 406C.

Anyone any ideas which is correct, or where there is an authoritative source.

Na+ and K+ are very similar chemically speaking, so perhaps the tendancy not to clump is in contrast to divalent ions like Ca++. --[1]


Some of this liguid was leaking from my ENERGIZER Batteries and I was terribly worried. —Preceding unsigned comment added by 98.203.94.16 (talk) 04:11, 27 March 2011 (UTC)

Melting point thought:[edit]

You may want to try the Handbook of Chemistry and Physics.

> The physical constants have been updated with their "CRC Handbook of Chemistry and Physics 2006" values


Reply: the melting point is indead 380 degrees. this is taken for the as chenistry revision guide and for exan pruposes this has to be correct

You have wonderful faith in the people who set exams (of whom I am one)! One problem with the measurement of the melting point of KOH is that it is pretty much never anhydrous: there is always some water associated with it, even as a melt. The more water, the lower the melting point (as for almost all mixtures). The melting point may also vary with the rate of heating and other experimental parameters. The only reason that a melting point is quoted at all is to show that KOH melts before it dehydrates to K2O. Physchim62 (talk) 10:14, 6 April 2007 (UTC)

Improvements[edit]

I've begun efforts to bring this article into accordance with the Wikipedia:Manual of Style.--YanA 00:26, 23 April 2007 (UTC)

Could somebody please replace all the superscripted hyphens (-) with a proper minus sign (−) = U+2211 superscripted ... or possibly a superscript minus sign (⁻) = U+207B. —DIV (138.194.12.32 (talk) 06:10, 25 September 2009 (UTC))
I checked the article page today for superscripted hyphens, none found. Use of the {{chem}} template seems to have done the trick. --Gnostic804 (talk) 22:05, 8 November 2010 (UTC)

Reactivity[edit]

Methanol[edit]

Sorry, I couldn't find where to make a new category for discussion but I just wanted to ask two questions. Is Potassium Hydroxide will react with Methanol? And What is the maximum solubility of Potassium Hydroxide in Methanol? —Preceding unsigned comment added by Marksiqi (talkcontribs) 07:14, 10 May 2008 (UTC)

Carbon Dioxide absorbant[edit]

In several novels, such as From the Earth to the Moon, and several non-fiction books, such as Blind Man's Bluff, crystals of caustic potash are used to remove carbon dioxide from the air in confined spaces. Is this accurate? If so, then by what process?RSido 19:42, 29 April 2007 (UTC)

Yes, after a bit of poking around, potassium hydroxide and for that matter many other things containing hydroxide ions can absorb CO2. You may want to check out this paper: Kucka, L.; Kenig, E. Y.; Górak, A Ind. Eng. Chem. Res. 2002, 41, 5952-5957. It doesn't go into the details about how it happens to much but it shows that KOH(aq) does indeed absorb CO2. They don't say much about the solid. --YanA 04:25, 2 May 2007 (UTC)
All alcali hydroxides are good absorbents of CO2, the reaction beeing: 2M+IOH(s) + CO2(g) → M+I2CO3·H2O(s), forming the corresponding alcali carbonate monohydrate; however, in most applications (e.g. submarines and space modules), lithium hydroxide, LiOH is used for this purpose, because of two properties:
1. Lithium has the lowest atomic mass of all alcali metals, resulting in LiOH having a molecular mass of only about 24; that's 58% of M of sodium hydroxide and only 41% of M of potassium hydroxide. This means, that, e.g. for absorbing/binding 1 kg of CO2, you need only about 1.1 kg of LiOH, instead of about 1.82 kg NaOH or 2.55 kg KOH, making the lithium hydroxide the most volume-effective alternative (meaning, that you need less than half of mass and volume of sodium hydroxide to bind equivalent amount of carbon dioxide, which is place-sparing and, in space technlogy, fuel-sparing).
2. LiOH is the least hygroscopic of all alcali hydroxides; while NaOH and KOH rapidly absorb air moisture, "caking" together and eventualy dissolving into lye, lithium hydroxide rests solid and thus, is easier to process into compact batteries for the use.--84.163.122.90 04:44, 28 October 2007 (UTC)

Added a lot of sources, but didnt sign in heh. Xeolyte 22:57, 16 October 2007 (UTC)

Food section[edit]

I believe the food section is referring to uses of common lye (sodium hydroxide), not Potassium hydroxide. This section should be deleted or moved. --Superbeecat 05:56, 29 June 2007 (UTC)


Both sodium and potassium hydroxides are used, sodium hydroxide prevalently, though. Sometimes, even mixtures of both are used. However, potassium hydroxide is a relevant food industry chemical.--84.163.122.90 04:23, 28 October 2007 (UTC)

Basicity[edit]

Add basicity to properties box, as per Caesium hydroxide. —DIV (128.250.80.15 (talk) 04:04, 4 March 2008 (UTC))

Claims in the current article (July 5, 08)[edit]

Responding to a suggestion that we "clean up" this article... The current article makes claims that are difficult to verify. When 750,000,000 kg/y of something is produced, inevitably many niche uses are examined, but Wikipedia is probably not the ideal repository for this kind of factoid collecting. Thus, I am skeptical about the significance of many (most?) of the applications claimed. I particularly question all of the claimed applications in food industry, I am sure all kinds of strange and fun stuff has been tried and is even useful somewhere, somehow. The more common NaOH (75,000,000,000 kg/y by my reckoning) is likely confused with KOH, which may be the source of some confusion. So I wanted to share these thoughts before editing the article. If anyone has suggestions, please leave a note here.--Smokefoot 00:05, 6 July 2008 (UTC)

If KOH is used interchangeably with NaOH, perhaps all the "interchangeable" stuff should be put at NaOH, with the KOH-specific applications left here (e.g. hygroscopicity, solubility in alcohols). We can of course, put a note that " ... since NaOH and KOH are cheap commodity chemicals with very similar aqueous behavior, they are easiliy substituted for each other." --Rifleman 82 (talk) 05:19, 6 July 2008 (UTC)


Uses[edit]

I'd like to see it mentioned that it is commonly used as a catalyst in the production of biodiesel from vegetable oil. —Preceding unsigned comment added by 213.100.137.147 (talk) 15:16, 17 October 2008 (UTC)

sublimes?[edit]

The current article revision states "KOH sublimes unchanged at 400 °C; the gaseous species is dimeric" which doesn't agree with the melting and boiling points given in the infobox (360 °C and 1320 °C). Either the melting and boiling points are not at 1 atm or the sublimation is in vacuum. I think the latter, because m.p. is confirmed by Aldrich (as 361 C) --Cubbi (talk) 19:01, 9 February 2009 (UTC)

Strongly basic? How much? (ph)[edit]

What is the strength of this chemical on the pH scale? I don't see that listed anywhere. The article says it is "strong", but that isn't an accurate enough definition. DMahalko (talk) 02:51, 5 April 2009 (UTC)

The pH of an aqueous solution of KOH depends on its concentration.
The usual way to measure the strength of an acid is with an acid dissociation constant, Ka, often quoted as a pKa. For bases, a base dissociation constant, Kb, can be calculated, again often quoted as a pKb. The use of pKb's was common in the olden days, but nowadays pKa's tend to be used for acids and bases.
I've been looking for the pKa of KOH, but haven't found it so far.
Ben (talk) 19:10, 5 April 2009 (UTC)
You don't need to "look up" pKa. As long as you have pKb from some (reliable) source then you can calculate pKa from pKb and pKw (well known) — for a given temperature — as per the simple equation in the article at base dissociation constant. —DIV (138.194.12.32 (talk) 06:02, 25 September 2009 (UTC))

Solubility[edit]

The article's Properties/Solubility and dessicating properties section states "Approximately 121 g of KOH will dissolve in 100 mL of water at room temperature...," but Infobox/Properties/Solubility in water cites "110 g/100 mL (25 °C)". Does the article's statement need some elaboration or does the Infox data need to be updated? (I'm qualified on this subject only as a copy editor.) Gnostic804 (talk) 00:52, 24 October 2010 (UTC)

Niche applications: Fyrite device[edit]

After first editing it, I moved the following sentence, authored by Dac28 on 4 Nov 2010, out of Niche applications to here and wrote Dac28 for help:

Potassium hydroxide is also used in a Fyrite device to measure concentrations of carbon dioxide in a volume of air.[citation needed]

Here's why:

  1. After my action, this section still contains this article's only unsourced statement, and I did not want to add to that count.
  2. Not knowing what a Fyrite device is or what it does or why it deserves to be mentioned here, I searched WP and found only a photo of a Fyrite tester, authored and uploaded by User:CambridgeBayWeather (who is, BTW, also a WP administrator) and linked only to his/her personal /Weather subpage, in connection with weather equipment and measurement of hydrogen and oxygen. No mention of carbon dioxide or air or KOH in the caption. And I have no idea whether the device in CambridgeBayWeather's photo is what Dac28 has in mind.
  3. No Fyrite tester article exists and, outside of the present article, there are no other hits on the word Fyrite on WP/en (I didn't search other languages) as of 00:42 CST 08 Nov 2010, and I have no clue what kind of references to look for. Do you think we should mention a device before we can explain it, particularly in the Niche applications section (cf. User:Smokefoot's "Claims in the current article" comments on the present page)?

I'm leaving this in the hope that Dac28, perhaps with CambridgeBayWeather's assistance, can come up with enough of a 'what' and 'how' and 'why' for this Fyrite device to resolve all but concern number one of the above to warrant either reinstating the statement to the article or creating a new article on the device. If not, ... anyone else? (I'm just a copy editor here.) --Gnostic804 (talk) 07:57, 8 November 2010 (UTC)

http://www.bacharach-asia.com/index.php?lay=show&ac=article&Id=499191&Ntype=3 --Rifleman 82 (talk) 16:02, 8 November 2010 (UTC)
Many thanks, Rifleman 82! Ideal photo on that page, too; looks like the "tester" in CambridgeBayWeather's photo. All: Here's what I have so far. A "Fyrite device" is a bench-scale, chemical gas analysis instrument « show CambridgeBayWeather's photo » that can analyze a mixed-gas sample for the presence and percentage concentration of either CO
2
or O
2
, depending upon which of two kinds of fluid is used to charge the instrument. I haven't looked through any of the available Fyrite instrument manuals yet, but the fluid used to analyze for carbon dioxide is probably the one that contains the KOH that Dac28 asserts, right? If so, is a Fyrite instrument an example of a use of KOH that exploits its reactivity with CO
2
, rather than its properties as a strong base? Also—and correct me if I'm wrong—the name "Fyrite" appears to be neither a trade name nor (I hope) the name of a living person, but is used in a way analogous to "Erlenmeyer flask" and "Bunsen burner." Now, much of this information probably belongs somewhere in WP other than the present article, but no WP page exists for just "Gas analyzer" (instrument) or just "Gas analysis" (unqualified). A WP-wide search for the first subject was not very useful to the objective here, but the same kind of search for the second subject turned up a wealth of possibilities in different kinds of gas analysis methods and technologies. Whilst I try to find one of those appropriate to wikilink to "Fyrite chemical gas analysis instrument" (my current working term), would anyone like to narrow the search by nominating a particular gas analysis|-izer subject page for me to vet first?
(As a "filter" for this project, an assumption that I have the chemistry background only of an honors-level U.S. high-school graduate of circa 1960 should give results I can use quickly.) My gratitude in advance for all assistance! --Gnostic804 (talk) 01:26, 9 November 2010 (UTC). Revision/deletion Gnostic804 (talk) 08:49, 9 November 2010 (UTC).
If it's that obscure, maybe it doesn't merit a mention here. I recall that most CO2 sensors use infrared spectrophotometry. --Rifleman 82 (talk) 02:13, 9 November 2010 (UTC)
About CO
2
sensors, that sounds right from what I've seen, too. I'm guessing that this thing is something that was in wider use before infrared spectrophotometry became available/affordable. Actually, I see relevance for a small mention here, but very small. --Gnostic804 (talk) 08:49, 9 November 2010 (UTC)

Thanks to the docs I got from Rifleman 82's posted URL, I got what I needed: a gold mine! Thank you very much, kind sir!

After browsing through some manufacturers' manuals and newly found WP articles, I already have a long to-do list on this matter, and it's going to get longer. There are more changes needed elsewhere in WP on this subject than for this KOH article. I have deleted the no-longer-applicable stuff from my earlier post of 01:26, 9 November 2010 (UTC). I found a relevant WP article to link to, and I know what not to call this "Fyrite" puppy (actually, it's a FYRITE® Orsat gas analyser, and that represents six challenges right there). Unfortunately, I'm to be otherwise occupied for a day or so before I can get back to work here and check in with an update. Sorry, but thanks to everyone in advance for your patience. --Gnostic804 (talk) 08:49, 9 November 2010 (UTC)


I suppose any strong base (LiOH or NaOH) would work. Don't see any considerations apart from price and availability. Perhaps an extended discussion and/or a redirect from Fyrite to Orsat gas analyzer is appropriate. If you need to stick it anywhere, the section "Reactions with inorganic compounds" may be best. Surprised that IR devices are expensive... $300 for a cigarette-pack sized device. Accuracy, perhaps? --Rifleman 82 (talk) 16:40, 9 November 2010 (UTC)
Since NaOH slowly reacts with glass, and since the original components of the Orsat gas analyzer were chiefly glass until the advent of clear plastic substitutes for laboratory glassware, I'm sure that, historically, KOH had to be used, if for no other reason than to prevent frosting of the glass "sight tube" used to visually read the level of the meniscus inside it during measurement. I've now looked at literature (largely German) on the Orsat apparatus from the late 19th and early 20th centuries and have found no mention of the use LiOH in volumetric gas analysis, so I can't speak to that.--Gnostic804 (talk) 00:27, 22 May 2011 (UTC)

A specific modern use for a Fyrite device is in the calibration and monitoring of incubators used to grow organisms (bacterial cultures, embryos for in vitro fertilization) that require CO2-controlled environment. Many of these incubators use thermal conductivity sensors (infrared-type sensors are often prohibitively expensive) to control CO2 concentration but reference standard is a Fyrite device. I'm looking for a cite-able source on this. So, Fyrite devices and the CO2 absorption properties of KOH definitely have modern use for at least science and medical applications. Megajason (talk) 06:32, 14 June 2013 (UTC)

How tens of thousands of tons are we talking about? Otherwise it is niche or niche-niche. --Smokefoot (talk) 13:27, 14 June 2013 (UTC)
The center component for that color reaction is pyrogallol, and KOH is mostly used as a base. But I think it's fair comment (and ought to go somewhere in the article) that KOH is less aggessive towards soft glass that in NaOH. We appreciate your campaign against trivia, but these protracted battles have a way of turning into crusades. Be aware of the dark side of the force. 128.226.130.48 (talk) 15:44, 14 June 2013 (UTC)

Melting Point - Source discussion[edit]

I originally updated the melting point to 360 C, as per ChemSpider's listing. That was undone, as CS wasn't deemed reliable enough, so I've gone ahead and added a citation listing Alfa Aesar. There's also this alternative version of the product listing and this Oakwood Chem listing. It's worth noting that there are two reputable sources citing 380 C, but both of those (1, 2) lead back to the NIH, which utilizes the same 1996 citation for both.

In other words - while there does seem to be some disagreement, 360 C is both the most recent and the most commonly cited melting point.

--BartholomewRSP (talk) 16:09, 26 October 2015 (UTC)