Talk:Calcium hydroxide

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A healthy food source of mineral Calcium ?[edit]

Humans need 1 g of it per day. It is much cheaper/convinient to eat this (Calcium hydroxide) than milk for calcium. Please advice. — Preceding unsigned comment added by Vwalvekar (talkcontribs)</spam>


The values of Ksp and solubility do not get along. They are related by Ksp=4x^3 or x=(Ksp/4)^(1/3)

If Ksp=4.68 you get 1.05E-2 M or 0.6145 g/L or 0.06145 g/100 mL. This is much less than the smallest of all numbers given.

Other sources, e.g. show Ksp=5.02E-6, producing 1.079E-2 M or 0.6291 g/L or 0.06291 g/100 mL.

Alternatively, if you use 0.173 g/100mL or 1.73 g/L you get 0.02338 M (Ca(OH)2 saturated concentration, or Ksp=5.11E-5 — Preceding unsigned comment added by (talk) 20:44, 26 September 2012 (UTC)[reply]

Flue Gas Desulfurization[edit]

There is no mention under industrial applications of wet scrubbing flue gas desulfurization. Granted, Calcium Hydroxide is not the initial principle reagant for that, CaO is, but by the time the flue gas comes in contact with the sorbent, it is Calcium Hydroxide.Woahmid (talk) 00:09, 29 February 2012 (UTC)[reply]


Lutefisk literally translates as "lye fish" so someone should check if it's lime or lye that is used. —Preceding unsigned comment added by (talk) 02:21, 5 December 2010 (UTC)[reply]


The impression you get from reading the hazards is that this stuff is dangerously toxic, it is not, however. I think this should be changed. (talk) 08:15, 22 April 2009 (UTC)[reply]

Can cause bad burns[edit]

True - not especially toxic - but can cause very bad burns - and while an acid burn hurts right away - if you get some in your shoe - with a little sweat or moisture it will feel slightly uncomfortable while it digests your skin - (Found out the hard way - removed my socks to find skin missing and bleeding - took a month to heal.) . — Preceding unsigned comment added by (talk) 15:14, 1 April 2015 (UTC)[reply]

Error Redirect[edit]

I wrote in Calcium Hydrate, and was redirected to Calcium Hydroxide. These are not the same thing. Calcium Hydrate is Ca·6H2O [or Ca(aq)] (i believe - I actually came to check the number of water molecules per calcium ion), while Calcium Hydroxide is Ca(OH)2. I would stop the redirect, but I don't know how. :( - Baribeau 01:38, 27 November 2006 (UTC)[reply]

Ca.6H2O exists only in solution. If you dissolve CaCl2 in water, you'll probably get Ca2+ . xH2O. But in solid form, the only thing that you can get is the hydroxide, probably with a lot of water in the crystal structure.
— Preceding unsigned comment added by (talk) 08:15, 2009 April 22 (UTC)

article division[edit]

There should be separate articles for slaked lime, lime water, milk of lime and common applications, and Calcium hydroxide, Magnesium hydroxide with Chemistry etc. Same goes for Calcium Oxide / lime (mineral). Comments please PeterGrecian 14:26, 19 Apr 2005 (UTC)

I disagree with this proposal. Put your effort into fleshing out this article and cleaning it up, as the tag asks us to. In the unlikely event that this one gets unwieldy, something could later be split out. Gene Nygaard 18:52, 6 October 2005 (UTC)[reply]
  • There are identical articles for calcium hydroxide, slaked lime and hydrated lime. Is triplication necessary or just a waste of reading time, not to mention confusing? GGBiscuit (talk) 20:22, 1 September 2013 (UTC)[reply]

clean up.[edit]

I agree with your comments. Also... the formatting of the article is poor with lines chopped in two. Perhaps it has been copied from somewhere - and there are copywrite issues? Also what on earth is polikar! It looks like something Russian? CustardJack 16:55, 11 May 2005 (UTC)[reply]

further cleanup[edit]

I have tried to cleanup the grammar and style problems, although a few clunky bits remain. In particular, I was unsure as to whether to change the word "drug" to "chemical" or "preservative" in the last line of the "Uses" section. Also, the line "Because of its strong basic properties, calcium hydroxide has many varied uses as:" is very cumbersome and should be edited further. I also believe the phrase "but unrelated to the citrus fruit (lime)" should be removed and a link to a lime disambiguafication page placed at the top of the article, but I'm running out of time for editing right now. -Paul Foster 9:08, 23 May 2005 (EST)

One question: As to the dangers through overdose section, can't the difficulty breathing and internal bleeding be explained by the hypotension? - Guest 4:09, 3 Feb 2007 (Pacific Time)

The article states: "When heated to 512 °C, the partial pressure of water in equilibrium with calcium hydroxide reaches 101 kPa and decomposes into calcium oxide and water." This sentence needs to be edited, but since I don't have access to the reference, I can't do it. As this sentence reads now, the partial pressure of water decomposes into calcium oxide and water, which is nonsensical. Partial pressures don't decompose. —Preceding unsigned comment added by (talk) 23:29, 27 May 2010 (UTC)[reply]

Tweaked. Materialscientist (talk) 23:34, 27 May 2010 (UTC)[reply]


Are their any methods of production that are cheap and don't produce CO2 Ozone 19:16, 28 February 2006 (UTC)[reply]

No!! . . . LinguisticDemographer 13:39, 17 March 2007 (UTC)[reply]

There are expensive methods, which does not produces CO2 (but produces SO2). Starting material there would be calcium sulfate. SO2 is worse for environment than CO2, and in such case it could not be filtered, because the cheapest material for removing SO2 from waste gas stream is calcium hydroxide itself. -Yyy (talk) 07:55, 2 March 2008 (UTC)[reply]


would it be possible to add an shortcut for Ca(OH)2?because not everybody looks for Calcium Oxide...

Merger with Portlandite[edit]

There might be some argument for merging Portlandite (which is the crystalline mineral) into this, but not vice versa. Its crystalline mineral nature is just one of many attributes of calcium hydroxide. . . . LinguisticDemographer 13:45, 17 March 2007 (UTC)[reply]

Celts and hair[edit]

Now, I've heard that the celts washed their hair with slaked lime, or Calcium hydroxide, and so made it stiff and, also, bleached it. However, I'm struggling to find out if you can actually do this with lime alone, or if there were other ingredients involved, or what?

The details, unfortuantely, are not particularly thick on the ground. Here's a couple of links with most of what I know -

' "Their hair is blond, and not only naturally so, but they also make it their practice by artificial means to increase the distinguishing colour which nature has given it. For they are always washing their hair in lime-water, and they pull it back from the forehead to the top of the head and back to the nape of the neck with the result that their appearance is like that of Satyrs and Pans, since the treatment of their hair makes it so heavy and coarse that it differs in no respect from the mane of horses" '

' The Celts bleached and spiked their hair with lime – one ancient writer wrote that each spike of hair was so sharp that an apple could be impaled on one! '

- I'd be very interested in knowing more about this, if anyone has the time to research it more deeply than I have. 15:15, 16 May 2007 (UTC)[reply]

Calcium Hydroxide is listed as the primary active ingredient in depilitory creams such as Nair. It seems doubtful that "The Celts" would be able to take a mineral form of this and use it on their hair, and still have hair. That's why we don't use just any random sources from the internet. Angryredplanet (talk) 20:05, 18 October 2021 (UTC)[reply]


One paragraph says Ca(OH)2 decomposes at 512 C, and the chembox at right says 580 C. Which is it? 10:02, 11 August 2007 (UTC)[reply]

Vapor pressure[edit]

In the intro there is a footnote that claims that 512°C is the temperature at which H2O vapor pressure reaches 101 kPa. What on earth is meant here? At 100°C the vapor pressure of water reaches 101 kPa and it boils. Maybe this is meant to refer to the partial pressure of H2O over Ca(OH)2? --Slashme (talk) 10:22, 21 January 2008 (UTC)[reply]

Yes, it must be the partial pressure of H2O in the equilibrium Ca(OH)2 -> CaO + H2O(g). --Itub (talk) 13:02, 21 January 2008 (UTC)[reply]

sea water[edit]

Is it possible to make by reaction with sea water, instead of pure water? If so, what additional substances would be made. (talk) 18:17, 15 November 2009 (UTC)[reply]

Metal and slaked lime[edit]

What happens if metal comes into contact with slaked lime? (talk) 02:46, 11 August 2010 (UTC)[reply]

The result depends on the metal, but for most commonly encountered metals, nothing would happen rapidly. In contact with base (such as Ca(OH)2) and water, most metals corrode to the oxides.--Smokefoot (talk) 14:19, 18 September 2010 (UTC)[reply]

Lutefisk? Really?[edit]

I'd like to see a cite about lutefisk made with calcium hydroxide, as opposed to lye. I'm skeptical that calcium hydroxide would even work. Francis Lima (talk) 21:31, 19 September 2010 (UTC)[reply]

Use in Mass Graves[edit]

I've read a lot about the use of lime for mass graves of plague victims, and have just been reading about the mass graves in the Holocaust. Nothing is mentioned of this usage here and I don't know enough about it to comment (or whether this is the right page!) - any help would be great. Jess xx (talk) 22:12, 19 June 2011 (UTC)[reply]

use in food[edit]

So ... It has a level 3 for health, but "has many practical uses, including food"? uh .... can someone explain/correct this? UNIT A4B1 (talk) 23:47, 30 November 2011 (UTC)[reply]

according to this site it is not suitable for use in paan because it is made from the shells of living animals.--Richardson mcphillips (talk) 17:49, 13 January 2014 (UTC)[reply]

Niche uses: Bulleting under Calcium Stearate[edit]

Under 'Niche Uses", the bulleting is tabbed in under Calcium stearate, so it appears that the following 8 bullets pertain to Calcium stearate. I have checked 4 of the items and they are still seem to be referring to Ca(OH)2. (Neither Ca stearate or Ca hydroxide is mentioned in brake pad or Ebonite wiki entries?). I was interested in the use of Ca hydroxide as an pesticide and had to check to see if it was in fact the stearate or hydroxide being referred to. This is my first entry on Wiki, so can someone else review and/or edit if necessary? Cornyvet (talk) 04:10, 22 April 2012 (UTC)[reply]

calcium hydroxide -- slaked lime: gesso?[edit]

I am trying to find a source for the slaked lime used to make gesso and it would be helpful to know if food grade calcium hydroxide is used for traditional gesso -- often called gesso sotile. It isn't mentioned in the many uses discussed on this page, but if it is the same thing, then it would make my search for a source very easy and it would also be useful to be included on the page in case other gilders or tempera artists are also looking. I was hoping that someone would know. Pbfasks (talk) 16:51, 25 April 2012 (UTC)[reply]

Rewrite this entire article[edit]

This article is dysfunctional or semi-functional at best. Can someone please take it upon themselves to do a rewrite (from scratch)? — Preceding unsigned comment added by Gibson88 (talkcontribs) 12:49, 3 June 2014 (UTC)[reply]

Quote: “Because it is produced on a large scale, is easily handled, and is cheap, myriad niche and even large-scale applications have been described. A partial listing follows:”

Have been described where? Applications have been described because it is cheap etc.? If this is a section for Niche Uses why has the phrase “…and even large-scale applications…” been included? I have amended this sentence to at least agree with the section heading:

“Calcium Hydroxide is produced on a large scale, is easily handled and is cheap. Numerous niche applications are in use. A partial listing follows:”

although I suspect that not all the applications listed are “niche”. For instance, the use of hydrated lime in making mortar is hardly a niche application. One of the standard mortar mixes in the UK building industry is 1:1:6 cement : hydrated lime: sand.

To differentiate between large-scale and niche applications one presumably needs information on the tonnage of material used in each application listed. Where is exactly is the dividing line between the two categories to be drawn? In the absence of tonnage information, I think it would probably be best to remove the Niche Uses section title completely and reorganise the various listed uses into several broad categories for the moment.

Altogether, this is a rather mixed-up section making up a major part of the article. I agree with the foregoing comment – a rewrite is needed. Freeman501 (talk) 07:58, 23 August 2014 (UTC)[reply]

Picture caption[edit]

It seems to me that the caption for the two types of corn kernels is reversed. The white ones have been treated and the yellow ones have not. The page on hominy has it right.

- Metricator — Preceding unsigned comment added by Metricator (talkcontribs) 01:04, 6 April 2015 (UTC)[reply]


pKb values in article are invalid and non-verifiable, due to the fact the referred content is not an original research neither gives any further references.

IUPAC buffers suggests for a saturated Ca(OH)2 solution at 25°C ph=12.45 -

By making approximation that Ca(OH)2 dissociated only once in the solution and concentration of calcium hydroxide ion [Ca(OH)+] approximately equals to concentration of hydroxide ion [HO-] ( Ca(OH)2 <=> Ca(OH)+ + HO- ), we can see that:

Water self ionization at 25°C Kw = [HO-][H+] = 1.0×10-14 (1) , logKw = 14.0 - ;

Kb = [Ca(OH)+]×[HO-] / [Ca(OH)2] ;

Provided concentration of calcium hydroxide ion [Ca(OH)+] approximately equals to concentration of hydroxide ion [HO-] ( due to Ca(OH)2 <=> Ca(OH)+ + HO- ), we get Kb = [HO-]2 / [Ca(OH)2] (2)

Combining the two equations (1) and (2) we can derrive the Kb values from [H+]:

Kb = (Kw/[H+])2 / [Ca(OH)2]

pKb = -log Kb , pKw = - log Kw, solubility of Ca(OH)2 at 25°C is approximately 1.67 g/L, yielding molar solubility of 22.5×10-6 mol/L, and pCa(OH)2 = -log[Ca(OH)2] = 4.65

Substituting the values with their negative logarithms we get:

pKb = (pKw - pH) × 2 - pCa(OH)2 = (14.0 - 12.45) × 2 - 4.65 = - 1.55

This value is not a first dissociation constant of calcium hydroxide (pKb1), it is lower than pKb1 due to the fact that second dissociation happens and because concentration of hydroxide ion is not equal to the concentration of calcium monohydroxide ion. Anticipated values of the first dissociation constant pKb1 for calcium hydroxide is in the range of -1.0..0.5, but measurements in this range are complicated and values vary from source to source.

IUPAC publication Dissociation Constants of Inorganic Acids and Bases in Aqueous Solution (1969) at p. 151-152 provides a collection of the references for different measurements of pKb values for Ca(OH)+ ion, with most values in the range of 1.02..1.51.

I'm going to edit the article and incorporate the final numbers and references into the article. (talk) 03:18, 17 June 2017 (UTC)[reply]

update: looking at concentrations of dissolved Ca(OH)2 ( 22.5×10-6 mol/L ) against concentration of hydroxide ( 35.5×10-3 mol/L ) it becomes clear, that many assumptions I've made are not appliacble due to the fact there's much more insoluble substance taking part in the reaction. So dissociation constant is not applicable to the first dissociation of calcium hydroxide and solubility product shall be used instead. — Preceding unsigned comment added by (talk) 06:06, 17 June 2017 (UTC)[reply]

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CO2 absorption[edit]

Since the issue here seems a little difficult to grasp for certain people: a) "reliable sources" does not include a crowdsourced homework help page. b) Even if this were a defensible statement, the lede is there to summarize article content, not add new material. You either treat this in the body, at a length that then justifies inclusion in the lede, or you leave it out entirely.

Stupid posturing is not a suitable replacement for addressing these issues, Brian Everlasting. And if I continue to see you revenge-revert my edits in other articles, you've got some exercise coming.--Elmidae (talk · contribs) 13:25, 27 August 2018 (UTC)[reply]

Further reading[edit]

@Smokefoot: This article is cited many times

  • Schotsmans, Eline M.J.; Denton, John; Dekeirsschieter, Jessica; Ivaneanu, Tatiana; Leentjes, Sarah; Janaway, Rob C.; Wilson, Andrew S. (April 2012). "Effects of hydrated lime and quicklime on the decay of buried human remains using pig cadavers as human body analogues". Forensic Science International. 217 (1–3): 50–59. doi:10.1016/j.forsciint.2011.09.025. PMID 22030481. Retrieved 12 May 2023.
.... 0mtwb9gd5wx (talk) 15:44, 12 May 2023 (UTC)[reply]

@0mtwb9gd5wx: >100,000 articles, patents, reports on Ca(OH)2. Over the preceding 10 years, more than 10 articles appear every day. That flux is the reason we in the chemistry project try to follow WP:SECONDARY and WP:TERTIARY for such massive topics.--Smokefoot (talk) 05:31, 13 May 2023 (UTC)[reply]