Talk:Self-ionization of water

Untitled

What are the kinetics of this reaction? -- The Anome 23:26, 13 Apr 2004 (UTC)

Minor

Minor edit to nomenclature. 213.120.90.59 Contributions 07:17, 25 Apr 2005 (UTC)

Some points

Notes: Water in motion will pick up charge from the air or from what it is in contact with. Therefore for water to be neutral, it must be at rest and at equilibrium. I'm not sure whether there is any difference if liquid water is exposed to SATP (100% RH) or not. I'd guess we probably can't measure the difference.

Significant deviations from the assumption stated in the article often occur in real world conditions. If I recall, in a 10% solution of NaOH the assumptions are not so good. Anyways, you can easily get to pH numbers (measuring the H/sup/+ concentration) well below zero, and to numbers above +14. ( with the fugacity diverging from that calculated from ion concentrations). Since now-a-days, Molarity isn't a good indication of a solution's "strength" (polymeric solutions have low Molarity), it should be stated that the assumptions are accurate in "dilute" aqueous solutions. Of course, the definition of dilute often rests on the accuracy of similar assumptions and makes the logic circular.

Vapor phase equilibria are not the same as for liquid water. Ion populations and H-bonding differ so that the numbers are different too. -DEN 6-17-2005 208.230.167.50 Contributions 12:57, 17 June 2005

Auto?

I thought it is more common to refer to this as autoionisation. As opposed to self-. Google hits are pretty close, and "self-" has the benefit of a hundred Wikipedia forks/copycats... -- Миборовский ^{U|T|C|M|E|Chugoku Banzai!} 02:05, 27 February 2006 (UTC)

Actually, "autoionis/zation" gets 200,000 hits while "self-ionis/zation" gets 16,000. -- Миборовский ^{U|T|C|M|E|Chugoku Banzai!} 02:06, 27 February 2006 (UTC)

I thought autoionization was more common also, but when I looked, "self ionization water" gets 473,000 Google hits compared to 131,000 for "auto ionization water". (The s for z variant is a small fraction of usage, and separating the words instead of using the hyphen includes both types in the search results.) So the present title seems OK for now. --Blainster 21:27, 28 February 2006 (UTC)

Omitting [H2O(l)]^2

Do we actually omit it ... I thought it was still there since the activity of pure water we take as unit. Is this correct? —Preceding unsigned comment added by 129.11.197.210 (talk • contribs)

Yes, you are right, but taking the activity as 1 equates to the same result. -postglock 12:34, 13 December 2006 (UTC)

Math-ize (LaTeX) the equations?

Since the maths equations TeX parser should give HTML for relatively simple equations, it could be easier (and cleaner) to just write the equations in TeX. Any objections? -Matt 15:39, 16 June 2007 (UTC)

None. EagleFalconn (talk) 13:02, 16 July 2008 (UTC)

Wow. I just realized I answered a query from 1 year ago, not earlier today. Damn. EagleFalconn (talk) 13:03, 16 July 2008 (UTC)

Rapid recombination

One point that could be added is that the recombination H3O+ + OH- is the fastest known (bimolecular) reaction. I would add this and the value of k at 25oC, but I don't have a source at hand, and also Petergans is in the middle of a major rewrite. Perhaps you know of a source for this statement. I think it was as first measured by Manfred Eigen in the 1950s. Dirac66 (talk) 15:18, 4 March 2011 (UTC)

Need to explain activities?

Shouldn't this article include some discussion on the true equilibrium dissociation constant which will include activity coefficients? For pure water, I realize that the activity coefficient for the water is essentially 1 but the activity coefficients for H+ and OH- will be ever so slightly different than 1 due to ionic strength as given by Debye-Huckel's law. I think it is OK to say all this is negligible in the end but seems like it should be explained from first principles instead of just jumping to the "apparent" dissociation constant — Preceding unsigned comment added by Stieltjes (talk • contribs) 17:22, 28 August 2012 (UTC)

We do now have a graph of the variation of pK_w with ionic strength, which is the most important consequence of the non-ideality and which is in fact not entirely negligible. I agree that it would be a good idea for someone to add a discussion which mentions activity coefficients and Debye-Huckel. Dirac66 (talk) 18:39, 28 August 2012 (UTC)

Omission of reference conentration in formula for pKw

Using the definition of Kw = [H3O+][OH-] necessitates division by reference concentration squared before applying the common logarithm, i.e. pKw = -log10([H3O+][OH-]/c0^2), might look like nitpicking but in my view it is important to be correct with units. — Preceding unsigned comment added by Bjodah (talk • contribs) 13:29, 2 June 2015 (UTC)

Shouldn't `1 Molar' be `1 molar'?

Shouldn't `1 Molar' be `1 molar'? (I'm not a chemist so don't have the confidence to make the change).

D.Wardle (talk) 05:13, 4 October 2016 (UTC)

Yes, you are correct. I checked three general chemistry books which all use a small m, as does the Wikipedia article Molar concentration. I will make the change. Dirac66 (talk) 23:26, 5 October 2016 (UTC)

Actually, I think this amount concentration should be in mol/kg (molal). The reason is that the standard state is expressed as molality by a decree of IUPAC, the body that regulates (thank God) the nomenclature in the field of chemistry. The standard states is what is used to make the magnitudes dimensionless, thus implies the unit. At 25 deg C, selection of "molar" or "molal" does not matter very much since 1 kg of water ~= 1 L. However, the selection can have a significant impact much higher temperatures, as those described in the subsequent section of the article.

The obligatory joke related to the problem goes like this. "What is 1+1? Thermodynamicist answer: "The answer is very simple. However, how do you define 1?" (End o joke.) The joke is meant to indicate that the selection of the standard state matters. Just my $0.02. Hope this helps. Cheers, Stan J. Klimas (talk) 21:43, 6 October 2016 (UTC)

H₃O⁺, or  H⁺?

Chemistry text are often written on a language, which talk about free  H⁺, instead of hydronium ions. Most of the current text, except a single paragraph beginning with "At 24.87 °C", is written on the more precise hydronium language. Please make the whole text coherent AND explain the history behind the two ways of talking. Many people will be confused, otherwise.

I am not a chemist, I do not know the second point either, so I prefer not to touch the text myself.

Above edit added by editor Gezameszena 27 December 2021. I agree that the article needs an initial History section to clarify the relationship between  H⁺ and H₃O⁺. The two tend to be used interchangeably in many contexts which confuses many readers. Dirac66 (talk) 22:55, 15 January 2022 (UTC)

I have now added the History section to explain why both  H⁺ (Arrhenius) and H₃O⁺ (Bronsted-Lowry) are used. It remains to make the whole text coherent concerning the notation for the cations. Dirac66 (talk) 02:16, 18 January 2022 (UTC)

Actually the rest of the article mostly considers H₃O⁺, so I have just added a sentence saying so. I think that is sufficient. Dirac66 (talk) 21:13, 8 February 2022 (UTC)