# Talk:Acid dissociation constant/Archive 1

## List of pKa values and compounds

Why is there a list?

good question - it just adds length to an article that is already too long. Would anyone mind if I removed it? Conrad.Irwin 17:30, 21 March 2007 (UTC)

shouldn't the last be pKe = pKa + pKb?

Yes, it should be. In addition, this page would probably be better placed under "acid dissociation constant" or simply "dissociation constant." I need to look up what my nearest chemistry book calls it. --ES2 19:00, 19 Aug 2004 (UTC)

In this case, Ke = Kw , so pKe = pKw = pKa + pKb

H Padleckas 15:09, 10 Apr 2005 (UTC)

Hi

It is wrong that the adicity constant ranges from 0 to 1. If the acid is almost totally disolved, the acidity constant will tend to infinity. It is true though, that the constant will tend to 0 if there is werry little disolution. /Asger Krüger 9 Nov 2004 This has been fixed. H Padleckas 15:09, 10 Apr 2005 (UTC)

## Table of pKa values

Something looks wrong in this table of pKa values. Why are a bunch of bases listed in what should be an acid's table? H Padleckas 15:17, 10 Apr 2005 (UTC)

Theres really nothing 'technically' wrong with listing a pKb as a pKa as long as you know the difference, I'm going to have to call the whole table suspect now. Phosphate doesn't have a pKa or a pKb, phosphate is an ion. It is not a compound. Same goes for Borate. I'm further suspect now because all those amines that are listed could be compounds, but they could also be organic groups. I vote we strike the table and include a reference to the link currently labeled number one in a "See Also" section. EagleFalconn 21:40, 10 Apr 2005 (UTC)

Couldn't we put "ammonium" and "pyridinium," for example, instead of "ammonia" and "pyridine"? Olin

We could do it for ammonium, but that wouldn't work for pyridine. To my knowledge, a protonated pyridine is just called...a protonated pyridine. EagleFalconn 05:54, 8 February 2006 (UTC)

Actually, a protonated pyridine IS called pyridinium! Olin

## cleanup

I performed a cleanup and got rid of a lot of redundant and wordy (in my opinion, at least) information. I don't think I changed the content of the article, just tried to make it more precise. Olin

## Separate basicity constant article

Shouldn't there really be a different basicity constant article? Olin 22:27, 18 February 2006 (UTC)

## pKa H2S

When clicking the link for Hydrogen sulfide in the pKa table (listed at 7.00), the specific article says the pKa is 6.89. A pretty big difference. Someone who knows for sure should change one of the articles.

• It's not as big a difference as it seems, and it is a value which has not been measured (to my knowledge) for several decades... Physchim62 (talk) 08:34, 7 June 2006 (UTC)

## Basicity formula

Inthe basicity formula, it reads: A–(aq) + H2O(l) ⇌ HA(aq) + OH–(aq)

Shouldn't the "A" (that I'm guessing means acid, at least in the acidic formula) be changed to B? B–(aq) + H2O(l) ⇌ HB(aq) + OH–(aq)

No. Once the H+ leaves, what is left is an acid, regardless of the direction of reaction.

## 1/3 of the way there

Hi, I have majorly rewritten the first part of this article - but after that, I dont understand what it is on about. I dont know whether someone who does understand could perhaps simplify what is there. I was going to add some stuff about the stability of the ion affecting it - but I am not sure if that is covered under Factors that determine the relative strengths of acids and bases. Acidity in non-aqueous solutions seems to be a bit example specific and I am not sure of its relevance. I hope that what I have done is OK, and hope someone can help with the rest.

Conrad.Irwin 17:27, 21 March 2007 (UTC)

I have recently re-written the core articles chemical equilibrium and equilibrium constant. I've now started to clean this one up, so far having done definitions and useage. I intend to do the rest in the next few days.

I wonder whether weak acid and strong acid should effectively be deleted by transferring the distinct content here and making them into redirects to this article. Any thoughts?

Petergans 16:34, 18 May 2007 (UTC) Finished the revision. Can we now go for concensus?Petergans 19:38, 19 May 2007 (UTC)

## Wonky intro

The intro says pKa applies to weak-acids. This is news to me, and futhermore pKas are supplied for strong acids later in the entry. --Belg4mit 21:55, 1 October 2007 (UTC)

I understand your point. The difficulty is that pK can only be measured when there is partial dissociation, that is, when the acid is "weak". The pK of a "strong" acid such as HCl must be measured in a medium which is more acidic than water.Petergans 06:41, 2 October 2007 (UTC)

## Peer review request

In addition to the issues I mention on the peer review page part of me feels like this article is too much of a collection of facts about acid dissociation constants. Perhaps its because I tend to evaluate articles from a teaching perspective, but I feel like the article lacks what I would call good pedagogical flow. Perhaps that single issue is even the source of my other issues with the article. Thoughts? EagleFalconn (talk) 13:41, 16 July 2008 (UTC)

To be more specific, the section "Usage" bothers me because it mentions the HH equation and goes through an exercise where it talks about calculating pH. I feel like that information is better served on the page for the HH eqn, and that we strike the material except to say that the Henderson Hasselbach equation uses pKa. On that note, part of me feels like a 'uses' section is somewhat futile. The strength of an acid has really broad ramifications for lots of things that it will do. We may be better off simply listing some particularly pertinent articles where there is an effect that is dependent on the strength of an acid.

I'm also not particularly comfortable with the explanations based on Pauling's Rules. To be honest, I've never heard of them before (which likely has something to do with it). I grasp the rules, I just didn't know that Pauling had enumerated them as such. I propose to provide a kinetics based argument in addition to, or possibly as a replacement of, the current explanation for "Factors affecting acid strength."

In "Importance of pKa values," I'm not quite clear on how protonation/deprotonation can affect color of a compound. Is there a particular example I should be thinking of? I propose merging this section with "Usage" and renaming to "Uses"

"Acidity in Nonaqueous Solutions" is a pretty strong section currently, I mostly want to flesh out some of the explanations (like explaining why the dielectric constant is important more thoroughly) and add a couple more kinetics arguments. EagleFalconn (talk) 14:34, 16 July 2008 (UTC)

Note that I have demoted the article to class C due to lack of citations. Otherwise, it meets Class B standards. EagleFalconn (talk) 16:55, 16 July 2008 (UTC)

I've added structures for fumaric and maleic acids as the images are already in WP. I'll look at the other issues raised in due course.
Just one point to make now: I strongly advise not to include anything about kinetics. Dissociation constants refer to equilibria and kinetics don't come into it except that forward and backward reaction rates are equal. This was extensively discussed when I revised law of mass action.
Regarding the table of values: there is a serious issue here, namely that published values for some acids cover a wide range. This is partly due to ionic strength differences, partly due to systematic errors. It would be a major undertaking to give citations. For example SC-databaselists 73 publications for succinic acid pK values! Petergans (talk) 11:08, 17 July 2008 (UTC)
I'll try to find a fairly authoritative source for the pKa values and mention that they're pulled out of a single reference, are mostly there for comparison, and can vary based on the measurement technique used. I'll probably pick the CRC, but we'll see depending on what I can find on Knovel. EagleFalconn (talk) 15:29, 17 July 2008 (UTC)

## Picture

The picture is fine, but the example is not, as I doubt if the pK of this alcohol is measurable in water. Why not use an obvious acid like acetic acid or the carbonic acid/bicarbonate equilibrium which is so important for pH regulation in the body (Buffer solution)? Petergans (talk) 09:59, 21 July 2008 (UTC)

Mostly I picked the molecule because it was the first one I popped out of Gaussview. I'll change it to acetic acid later today. EagleFalconn (talk) 13:18, 21 July 2008 (UTC)

## Structure

I have finished with the chemical content, which should now be much more comprehensible to the general reader. I'll leave the re-organization to you guys/gals as it's probably better done by non-specialists. Petergans (talk) 17:14, 22 July 2008 (UTC)

I used pK in to the intro because the comments apply to both pKa and pKb. Petergans (talk) 19:44, 23 July 2008 (UTC)

## Citation

Hey Peter, both our article and the equilibrium constant article cite F.J,C. Rossotti and H. Rossotti, The Determination of Stability Constants, McGraw-Hill, 1961. for the relationship between activity and concentration. I was wondering if you actually owned a copy and could get a page number, or short of that if we could get a more modern reference. Google Books has the book, but its in 'snippet' form only. I could go to Scifinder and pull a paper out of the literature, but I personally favor secondary sources when available. EagleFalconn (talk) 12:56, 24 July 2008 (UTC)

Yes, I have a personal copy. I don't know how to reference individual pages without citing the book every time. Do you know how to do it? It's an old book, but I don't know of anything better in terms of coverage and throughness.
Chapter 2, p17 "Activity and concentration quotients"
2-1, p19 "Control of activity coefficients"
2-1A p 20 "Composition of the ionic medium"
2-1B p 23 "Limitations of the constant ionic medium method"

Petergans (talk) 15:34, 24 July 2008 (UTC)

I've looked into citing individual pages instead of the entire book every time. I've figured out how, but it'll take a little time to reformat the way we're referencing the book from my understanding. I'll get around to it at some point, for now if you've got page numbers for stuff just go ahead and cite the whole book and I'll fix it later. The {{cite_book}} template is one way to do it for now for books that don't already have a template like Greenwood and Earnshaw already does (though its pretty easy to create one, I made one the one for Loudon for this article). The main reason I object to older books that aren't available on something like Google books is simply accessability. When I get off internship (in like a month...), I'll see if I can find something in my thermo textbook that'll fit, as at least something from a book in print will be slightly more accessable. EagleFalconn (talk) 17:13, 24 July 2008 (UTC)
These is a brief section on ionic media in M.T. Beck and I. Nagypal, Chemistry of Complex Equilibria, published jointly by Akademiai Kado and Ellis Horwood, 1990 pp 355-341. I didn't want to cite this in the article because the book is about metal ion complexes which won't be much help in relation to pKa. Otherwise, Rossotti and Rossotti is the classic. The coverage of ionic medium is thorough and up to date(!) as the topic had been just about worked out by the time they published. I'll ask my friend Les Pettit if he knows of something more recent. Petergans (talk) 12:09, 25 July 2008 (UTC)

## Metal ions?

All metal ions in water are weak acids, but some are not as weak as others. for example,

${\displaystyle Al(OH)_{6}^{3+}+H_{2}O\rightleftharpoons Al(OH)_{5}(OH)^{2+}+H_{3}O^{+}}$, pK_a = 5 (Housecroft & Sharpe)

Should this be included in the article? There is a problem: the hydrolysis may progress further to polynuclear hydroxo complexes, so the first dissociation constant may not tell the whole story. Reference to Baes, C.F.; Mesmer, R.E.The Hydrolysis of Cations, (1976),Wiley, New York for detailed discussion relating to all metal ions Petergans (talk) 17:48, 25 July 2008 (UTC)

I think it'd be better dealt with an on article detailing metal ion behavior in solutions. While there is a pKa to be measured there, I don't think its our goal to relate in this article everything you can measure the pKa of. That said, it is biased in explanation towards solubility and identifying a specific compound as an acid. I think it merits at least mentioning the behavior of metal ions as lewis acids, but not much more. EagleFalconn (talk) 05:46, 26 July 2008 (UTC)

## Goldmine

Thermodynamic Quantities for the Ionization Reactions of BuffersRobert N. Goldberg,a Nand Kishore,b and Rebecca M. Lennen Biotechnology Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 ~Received 21 June 2001; accepted 16 September 2001; published 24 April 2002! This review contains selected values of thermodynamic quantities for the aqueous ionization reactions of 64 buffers, many of which are used in biological research. Since the aim is to be able to predict values of the ionization constant at temperatures not too far from ambient, the thermodynamic quantities which are tabulated are the pK, standard molar Gibbs energy DrG+, standard molar enthalpy DrH°, and standard molar heat capacity change DrCp + for each of the ionization reactions at the temperature T 5298.15K and the pressure p50.1 MPa. The standard state is the hypothetical ideal solution of unit molality. The chemical name~s! and CAS registry number, structure, empirical formula, and molecular weight are given for each buffer considered herein. The selection of the values of the thermodynamic quantities for each buffer is discussed. © 2002 by the U.S. Secretary of Commerce on behalf of the United States. All rights reserved.

## Infoboxes

I'm going to put back the chemical equilibria box under the acid-base box. I figure pKa falls within both, so it'll be helpful to have both present. EagleFalconn (talk) 13:11, 29 July 2008 (UTC)

## Hydrogen ion/Ammonia picture

Hey Peter, what kind of image are you looking for for the hydrogen ion/ammonia thing? I don't necessarily think the coordinate covalent bond thing is particularly instructive...I can make a ball and stick model similar to the one I made for the top right, or something else if you've got something in particular in mind. EagleFalconn (talk) 13:55, 29 July 2008 (UTC)

I wasn't looking for anything in particular, just found the image but decided against using it. We are running out of space on the right with the two navigation templates. Incidentally, I've re-done the speciation diagram with reduced width, but as the old diagram has been moved I'm not sure how to replace it.
More pertinently, We are just left with the applications section to enlarge. If you are just finishing an internship I guess you won't want to spend much time on WP. We have to avoid working on the same topic, so here is my list of suggestions, in no particular order.
• biochemistry, roughly as is at present
• buffer solutions
• pH indicators
• metal ion complexes

In addition, I think the table of pK values needs re-doing again, perhaps using data from the goldmine which is critically selected. I would also like to include the Delta H values, which will give more sense to the (to be expanded) thermodynamics section.

I've added a pKa and thermodynamic value table in addition to the one we already have. The reason for this is because quite honestly the goldmine has a lot of buffers and stuff that, quite honestly, I don't think are very instructive. I picked out the examples that I thought should be relatively recognizable and put them in the table though next to their thermo data. Sorry the table isn't as straightforward to read as I would like, but thats the form the data is in as given. EagleFalconn (talk) 20:09, 31 July 2008 (UTC)

Regarding the lifetime of the bare proton. I'm assuming that it is simply diffusion limited.

Let me know how you would like to proceed. Petergans (talk) 16:45, 29 July 2008 (UTC)

Sorry about the moving, I updated the picture to follow the naming convention we were using in the article which wound up moving it to the Wikimedia Commons. You'll need a Commons login (which is easy to get) and then unify it with your Wikipedia account. Click the link where it links to the description page on the commons to update it if you've actually changed its content. If you only want to change the width at which the image appears, you just need to change its Wikicode. See Help:Images_and_other_uploaded_files.

Don't worry about my WP time, I'm using it as something to do between experiments (which don't always require monitoring). I generally agree with your list items for the application section. I'm trying to think of other cases where the strength of an acid needs to be taken into account...we might want to have some kind of a general discussion of acid-base chemistry, possibly a summary of Acid-base reaction.

I'll take care of redoing the pK table, and perhaps retitle it to a more generic data table and include the thermodynamic data on there as well.

The lifetime of the bare proton is almost undoubtedly diffusion limited, but I feel like the statement is specific enough to require a citation.

Regarding citations, I've been looking into the MoS and I think the way we're doing things ok. There is the Harvard citation style and Wikipedia supports it, but its been outdated by the <ref> tags. I'm going to leave our citation style as is.

Once we take care of the Application section, I'm going to post a notice on Wikipedia Talk:WikiProject Chemistry for Class A review. At that point, we're theoretically at the level where we should request WP:FAC for the article. Feeling up to it? I know you've been doing a majority of the edits lately, but I'd try to help with that as best I could. EagleFalconn (talk) 18:02, 29 July 2008 (UTC)

## Titrations ?

Have a look at User:Petergans/sandbox. I've put together an outline of another little section, but I'm not sure if it should be included. Before doing any more work on it, I'd welcome opinions. Petergans (talk) 14:39, 30 July 2008 (UTC)

Its a little terse at the moment (which makes sense since its a first draft). I think it'd make an excellent addition to the article on titrations, which appears to have come to a consensus about breaking out a separate article on titration curves, for which your addition would make an excellent expansion. For this article, though, I think its sufficient to mention the application to titrations and provide a wikilink in a section about applications/importance. EagleFalconn (talk) 15:12, 30 July 2008 (UTC)

## Final polish

I'm definitely up for going after FA status. I hope that all the essential things are covered and that all that is needed now (apart from some minor corrections) is a final polish. EagleFalconn - your contribution has been crucial and much appreciated. Petergans (talk) 13:39, 31 July 2008 (UTC)

Much appreciated Peter. My goals for today (in order):

• Take into account Itub's comments as best as possible, particularly the ones I replied to.
• Re-read the article in its entirety forwards and then backwards for copyediting.
• Make a posting on WikiProject Chemistry requesting Class A review. I suppose we should've started at Good Article, but quite honestly the changes were made so fast over the past two weeks (Its only been 15 days and 58 edits! You should see the diff!) it wouldn't have been worth it.

EagleFalconn (talk) 13:56, 31 July 2008 (UTC)

I've revised thermodynamics, and decided to replace the table by an HTML table, mainly because of the much greater flexibility in presentation that it allows. I use Dreamweaver to draft the table and then paste it into WP. It's so much easier to use a WISYWIG editor! I've also corrected the errors that Ivan (user:itub) spotted. Petergans (talk) 20:27, 1 August 2008 (UTC)

Personally I prefer the Wikitable because its easier to read. I do prefer your presentation of the table though. I'm going to convert it to a Wikitable at User:EagleFalconn/ThermoSandbox and let you know when I'm done with it. EagleFalconn (talk) 21:26, 1 August 2008 (UTC)

## Unicode, Ugh

I hate ⇌ for the equilibrium sign - it's virtually unreadable. Much better to use ${\displaystyle \rightleftharpoons }$. I doubt if that goes against the accepted style guidelines. Petergans (talk) 12:30, 2 August 2008 (UTC)

As a matter of fact it does. I'm trying to get the style guidelines changed so that the reactions and math on this article with both be readable. As of right now, style guidelines forbid the use of the [itex] tags inline (which I generally agree with as it can cause odd linebreaks sometimes), but also forbids their use for reactions to make the articles "more accessable" for editing by chem-savvy people. Also, theres another good reason for the LaTeX to not be used - apparently in Internet Explorer it causes some kind of bug that makes the character unrenderable. If you'd like to help me, please go to Wikipedia_talk:WikiProject_Chemicals/Style_guidelines#WP:CHEMSTYLE_for_Reactions as I am currently losing quite badly. EagleFalconn (talk) 16:18, 2 August 2008 (UTC)

I've put in a strongly worded contribution. If we don't get agreement I think we should go ahead anyway with ${\displaystyle \rightleftharpoons }$ because of the legibility issue. Petergans (talk) 19:49, 2 August 2008 (UTC)

For now, I'm going to Wikipedia:Ignore all rules and do what I want. I'll replace the equilibrium signs now and see if the mixed HTML/LaTeX format grows on me. Whats your opinion on HTML rendering for reactions, in particular when combined closely with LaTeX as this article currently is? EagleFalconn (talk) 20:11, 2 August 2008 (UTC)

It is a fundamental flaw in WP that there is no control of character size in LaTeX, as there is in equation editor in Word. Also, that there are no options for default settings in LaTeX, so that letters are rendered in italic by default. This means that we can never be fully consistent as between equations using \frac and HTML: even when the chemical symbols are enclosed in \mbox{ } they are a different size.
${\displaystyle K_{\mbox{a}}={\frac {[{\mbox{A}}^{-}][{\mbox{H}}^{+}]}{[{\mbox{AH}}]}}}$
Reluctantly, I have to concede that this does look better than when the letters are in italic. It's a pain, and the source becomes virtually unreadable. Note how non-alphabetic characters must be outside the mbox. Using \text instead of \mbox is no better. Are there any precedents in previous FA articles?
I notice that the default font in Wikitable is not the same as for text. It may be possible to use a font property <font face="TimesNewRoman" >text</font>, but I assume that it would have to be applied individually every time as the HTML <table> tag does not permit a font property.
Regarding the final table, I suggest a heading (or table footnote) such as "data from <ref> ...</ref>..." rather than individual references. I think that any pK value greater than 12.5 should be removed as I suspect that the values are not for water. This opens the question of whether some values for DMSO should also be quoted, maybe in the section on non-aqueous solutions? Petergans (talk) 07:50, 3 August 2008 (UTC)
I tried \mathrm. It's somewhat easier to apply than \mbox and gives much the same result.
${\displaystyle K_{\mbox{a}}=\mathrm {\frac {[A^{-}][H^{+}]}{[AH]}} }$
I still don't like the character size difference between HTML and LaTeX equations. Petergans (talk) 14:56, 3 August 2008 (UTC)

Petergans (talk) 14:56, 3 August 2008 (UTC)

I'm not really a big fan of the character size diferences either, but we'll work with what we've got. The sources I used for the pKas are pretty reliable. Lange's is a standard, highly regarded reference. The Knovel Critical Tables is also well known, but not as widely used since it requires a subscription to Knovel. My guess is that the values above 12.5 are from theory. The problem with not citing individual molecules on the table is that because I used 3 sources, I couldn't come up with a better way to indicate which was from which source. I don't think it clutters the appearance though. If you've got some DMSO pKa values feel free to use them, I don't have access to any that I know of. I'll start converting equations using \mathrm. EagleFalconn (talk) 17:55, 3 August 2008 (UTC)

## Featured Article Candidate?

Hi Peter, I'm looking at listing this article at WP:FAC now. Do you have any objections or a reason for me to wait? EagleFalconn (talk) 16:53, 4 August 2008 (UTC)

I'm not Peter, but if you want my advice I don't think the article is ready yet. Even if the content is perfect, you'll see that the FA nomination goes into excruciating detail regarding style. This includes some style rules you may not have even imagined existed! For example, minus signs should be − (you can find it in the "Insert" box under the edit summary line when you edit a page) and not the hyphen that shows up when you push the "minus" key in your keyboard. There are rules regarding non-breaking spaces between values and unit symbols; the degree sign in °C should be the correct character; bold should not be used for emphasis (basically don't use it anywhere except in the lead paragraph to highlight the title of the article); en dashes should be used for page ranges and some other uses; and many other rules. Submitting the article at this time would be an exercise in frustration because many will oppose based on these style rules. I suggest you first try to comply with all the style rules as best as you can before nominating the article. See WP:MOS and WP:MOSNUM for the gory details, or look at some of the recent FA candidates to see what the common objections are. --Itub (talk) 17:11, 4 August 2008 (UTC)
Another style rule: variables should be set in italics. This includes the K for equilibrium constant. The conventional style for pKa is pKa (this is the style recommended by the ACS Style Guide). --Itub (talk) 17:26, 4 August 2008 (UTC)

I hate to come off as a whiner, but wow. And people say that using LaTeX for chemical reactions is a barrier to entry for Wikipedia. EagleFalconn (talk) 18:22, 4 August 2008 (UTC)

The FA process certainly presents quite a barrier. But we have some people who know the ropes and are willing to help. --Itub (talk) 19:06, 4 August 2008 (UTC)
What concerns me is much more the content than the style. We have just about got the content right. I've contacted Ivo Leito (2nd in the list of links; I know him and we have published a paper together) to see if he can help with a table of pKa values for AN and DMSO. I've been trying to check the data in the last table on aniline, diethylene glycol and glycerol, which I think are wrong, but without success so far. Otherwise there are a few minor niggles which I'll be looking at in the next few days.
As for the question of style, what Ivan says about variables in italics is a generally accepted convention. As for the rest I marvel at it but I guess we have to comply. When publishing in journals etc. the editors and type-setters look after most of the style issues mentioned above, but in WP we have to do it ourselves. Remember, though, style must never take precedence over content. Petergans (talk) 22:35, 4 August 2008 (UTC)

I've been working on some of the style issues I've seen, but I'm not done yet (maybe later this week, if no one beats me to it). There are two more things that you need to be prepared for for the FA candidacy: 1) some may complain that the article is too technical, so anything that can be done to make it more understandable to the "general reader" should be done in advance; 2) others may complain that it doesn't have enough references (featured articles usually have at least 50 references!), so make sure that anything that could conceivably look questionable has a footnote. Since this is a basic chemistry topic, for many things repeated footnotes referring to the same physical or analytical chemistry textbook could be an option. --Itub (talk) 17:05, 5 August 2008 (UTC)

## Entropy term for ammonia and amines

Where do the TΔS values for ammonia and amines come from? The table says ΔH = 51.95 kJ/mol and TΔS = 104.7 kJ/mol. Yet, when I look at the Goldberg reference, I see ΔH = 51.95 kJ/mol and ΔG = 52.771 kJ/mol. Since ΔG = ΔH − TΔS, the value of −TΔS must be the difference, 0.821 kJ/mol. --Itub (talk) 08:55, 5 August 2008 (UTC)

I calculated the TΔS values in a spreadsheet using the Goldberg data for pK and ΔH values and ΔG = -5.706 pK. I then rounded the TΔS values according to the number of significant figures in the pK value, but this was not done in the spreadsheet which I have converted unchanged to this wikitable.
pK DG DH TDS
Acetate 4.756 -27.14 -0.41 26.73
Glycine 2.351 -13.41 4.00 17.41
9.78 -55.80 44.20 100.00
maleic 1.92 -10.96 1.10 12.06
6.27 -35.78 -3.60 32.18
Citrate 3.128 -17.85 4.07 21.92
4.76 -27.17 2.23 29.40
6.40 -36.50 -3.38 33.12
boric 9.237 -52.71 13.80 66.51
HSO4 1.987 -11.34 -22.40 -11.06
Oxalate 1.27 -7.25 -3.90 3.35
4.27 -24.34 -7.00 17.34
Phosphate 2.148 -12.26 -8.00 4.26
7.20 -41.07 3.60 44.67
12.35 -70.47 16.00 86.47
ammonia 9.245 -52.75 51.95 104.70
Methylamine 10.645 -60.74 55.34 116.08
Triethylamine 10.72 -61.17 43.13 104.30
Do you agree with these values? It appears that the dissociation of the ammonium ions is strongly endothermic, but I didn't think that this was worth commenting on in the text because there are only three exmples. Petergans (talk) 10:59, 5 August 2008 (UTC)
All the ΔG's have the wrong sign, which in turn results in the wrong value for TΔS. Remember that if this is a dissociation constant for a weak acid, ΔG has to be positive, because the reaction is not "spontaneous". Note that Goldberg already gives values for ΔG, so you don't need to compute them yourself. --Itub (talk) 11:09, 5 August 2008 (UTC)
The correct conversion factor, which reproduces the ΔG values given by Goldberg as a function of pKa, is ΔG = 5.7080 pK. --Itub (talk) 11:15, 5 August 2008 (UTC)
Thanks for this correction. I was working from Table 8 which does not have ΔG values and forgot that we are talking dissociation - I'm so used to working with association constants that the ΔG values did not look stupid! I'll now correct the table and the commentary.
Thanks also for bringing the article into line with house style.

Petergans (talk) 13:11, 5 August 2008 (UTC)

## Speciation

Diagram for monoprotic acid replaced and diagram for citric acid added. Style cleaned up. Unfortunately some of Ivan's edits earlier today on this section may have been lost, but I'm not sure of the details; sorry about that! Petergans (talk) 13:40, 6 August 2008 (UTC)

Looks good, just remember to add the official license templates (public domain, GFDL, or so) to the figures you uploaded. If you don't, you'll soon get a message from a robot threatening to delete the images. --Itub (talk) 14:20, 6 August 2008 (UTC)

## Definition cleanup by Petergans

Hey Peter, a couple comments/questions on your last edit on the Definitions section.

Is there any reason you prefer not to link to HSAB? I know its empirical, but its well taught and acknowledged to be quite correct. Also, the link to HSAB provides context for why charge to volume ratio matters.

Regarding the solvation shell of hydronium: The reference we are using at the moment cites H3O+ 6 H2O as the most common state (page 7812, table 2). It says the hydration number of the hydrogen ion is 6.9, and he corroborates that value with Shi, Z.; Ford, J. V.; Wei, S.; Castleman, A. W., Jr. J. Chem. Phys. 1993, 99, 8009-8015, which reports 6.7 ± 0.7. Am I misreading?

The quote at the end "protonation with respect to water, deprotation with respect to ammonia" is there because we are talking about the inaccuracies in the terminology typically used and cite a particular example of a reaction. It seems reasonable if we're discussion inaccuracies to give a version of the accurate terminology so that the reader knows how to read the article properly.

EagleFalconn (talk) 19:46, 6 August 2008 (UTC)

• I quote from Shriver and Atkins, Inorganic Chemistry, p167, introducing HSAB: "The proton, [H+],was the key electron pair acceptor in the discussion of Brønsted acid and base strengths. When considering Lewis acids and bases we must allow for a greater variety of acceptors and hence more factors that influence the interactions between electron pair donors and acceptors in general." I believe that HSAB theory is not relevant to acid dissociation constants for two reasons: i) it relates principally to Lewis acids and bases and ii) it is not a quantitative theory whereas pK values are quantitative.
• The question of "solvation shell" opens up a whole can of worms, to do with hydrogen bonding in water. Prior to quantum mechanical calculations the species H9O4+ was reasonably well established on the basis of experimental data. An actual structure is easy to imagine with three primary hydrogen bonds H2Oδ-:→Hδ+—OH2+. Maybe you could do a picture of these ions? Undoubtedly further hydrogen bonding with water molecules occurs, just as in pure water there are "clusters"; these are discussed in the article hydronium ion, which includes mention of the 6-hydrate as the mean composition. Because of the complexity of the topic I chose to use the phrase "H9O4+ and higher hydrates" because in reality a variety of structures co-exist.
• A protonation reaction is one in which a proton is added to another molecule, B, forming a B—H bond. This is not inaccurate, just that the proton has to extracted from a species H—A in order to interact with the Lewis base. Likewise a deprotonation reaction is one in which a proton is removed. Looking at the reactions from the point of view of of the molecule B, the terms protonation and deprotonation are correct. Maybe this isn't expressed clearly enough - my writing style tends to be rather terse, though I would rather use the term concise ;-). Petergans (talk) 08:35, 7 August 2008 (UTC)

We should look at <ref>{{cite book |title=The physical chemistry of natural waters |last=Millero |first=F.J. |year=2001 |publisher=Wiley |location=New York |isbn=0471362786 }}</ref>. I haven't done so, but I expect it to have a lot of stuff on activity coefficients and ionic strength. Additional source to Rossotti's? Petergans (talk) 10:06, 7 August 2008 (UTC)

• I agree that HSAB is not a quantitative theory. But we're not asking for a quantitative discussion at this particular point. We're saying that the proton is a very very reactive entity, and HSAB provides the rationale for that. Put another way, we're talking about charge/size ratio right now in that paragraph. Why does charge to size ratio matter? The reason for this falls within the domain of HSAB.
• I agree that with a molecule like water, its difficult to define clusters since everything is hydrogen bonded anyway. But the source specifically mentions the heptahydrated proton as the mean. Since it is the most common configuration, and since its the only one our current source mentions, we should speak to that one, not the easier to conceptualize one. Also, the paper in question here is experimental, as is the source that it cites.
• The issue isn't with the inaccuracy of your writing, its an issue with the inaccuracy in the terminology. To say that HA + B -> HB + A is a "protonation" reaction doesn't do it justice, because not everything is protonated, nor is it clear that all the primary structures we are concerned with are protonated. For example, if we had 2HA + B + C -> 2A + HB + HC where HA is HCl and B and C are two amines, it'd be safe to call it a protonation because we probably don't care about HCl and are just using as a source of protons.
On the other hand, in generic HA + B -> HB + A its not clear that we don't care about A, but only calling it protonation falsely implies that everything is protonated. As you say, to call the reaction a protonation you have to view it from the 'perspective' of molecule B, but in the context of this article (and in general, in my opinion) its not clear why you would should do that. The point of the comment was to acknowledge the general inaccuracy so that when the term protonation is used later, they understand that for this to take place, for one thing to be protonated something else has to be deprotonated.
• I'd be willing to look at the book but I don't have access to a university library at the moment. I can evaluate papers, but thats about it for now.

EagleFalconn (talk) 13:12, 7 August 2008 (UTC)

Here's my view on these question, in case it helps:
• I don't think HSAB says that H+ "is an exceptionally powerful Lewis acid and it will react with nearly any molecule it encounters". It just says that it is a hard acid, and that therefore it should prefer to bind to hard bases. But in fact I'd say it is treated as an outcast of sorts from the HSAB theory, because it has no electrons and is "off the charts" when compared to all the other hard acids. I concur with Peter that it is not clear that it is useful to mention HSAB in this article.
• There's some risk with confusing molecules with solvated clusters. H3O+ is a molecule (or an ion, if one insists that molecules have to be neutral). H52O+ is also a molecule: the proton in the middle is covalently bound to both oxygens in a three-center-four-electron bond, or is in the middle of a very strong symmetric hydrogen bond, depending on the point of view. For H9O4+, I'm not so sure. If I remember correctly, the hydrogen bonds are no longer symmetric, and one can start thinking of it as an H3O+ that is involved in three hydrogen bonds. For larger clusters, things get even blurrier. Also, if we insist on saying that the "real" proton species is H15O7+, we start losing sight of what is really special about the proton vs what is true of nearly every solvated species. For example, if you dissolve argon in water, I'm pretty sure that it will also have a solvation shell comprising somewhere around six waters, but that's just for inevitable geometric reasons. Saying that "free" argon does not exist in solution would not even be in the same league as saying that there are no free protons in solution, because the proton, unlike many solutes (but like metal cations), forms strong covalent bonds with the solvent. However, it only forms two such bonds because of size (and orbital) constraints, whereas metals typically form six bonds. Bottom line after all this rambling: I think this discussion is too much detail for this article and it would be best to include just a very brief statement and refer the reader to more specialized articles such as hydronium.
• I would call it a proton transfer reaction and mention that, when one focuses one's attention on one of the two species, one can think of it as a protonation or a deprotonation. A typical example is in organic chemistry, where the organic chemist only cares about what happens to the organic molecule of interest, whereas the other (typically inorganic) acid or base is just a "reagent" that one adds in order to effect the protonation or deprotonation of the organic molecule. --Itub (talk) 13:40, 7 August 2008 (UTC)
• If HSAB isn't appropriate, then why does charge to size ratio matter in terms of the reactivity of a proton? I'm just looking for some kind of a justification for the reader, and picked HSAB because I've understood that charge to size comes from that theory. Is there somewhere else we can get it from?
• I'm not particularly attached to calling it anything. My only point is that the current source we are using and its corroborating source both specifically call out the heptahydrate as the most common form and do not mention any other hydrates. So we're going to need a new source, especially since as the hydronium article specifically mentions and cites that "Recent work indicates that both [H5O2+ and H9O4+] represent ideal structures in a more general hydrogen bond network defect," which if I'm reading correctly means that they are not isolatable, unique structures and are substructures of a larger network (Ref: Marx, D.; Tuckerman, M. E.; Hutter, J. & Parrinello, M. (1999) The nature of the hydrated excess proton in water. Nature 397 601-604).
• Sounds reasonable. Its what I was trying to get across, I think.

EagleFalconn (talk) 13:54, 7 August 2008 (UTC)

I don't think we should get too hung up on the state of hydration of H3O+; various structures are known in the solid state (Greenwood&Earnshaw, 2nd edition, p 630, including H9O4+, but no reference). The situation in solution is fluid, to coin a phrase. Maybe we should limit ourselves to saying that the hydronium ion is further solvated.

As for "protonation", what I was trying to get at is the fact that this term is, rightly or wrongly, in common usage, as indicated by the existence of the article protonation. Petergans (talk) 16:48, 7 August 2008 (UTC)

## Comment on Zavitas paper

I've just read the summary. The results are totally unconvincing for this reason: different solvation numbers are obtained when different techniques are used. This is discussed at length in Metal ions in solution by John Burgess, chaper 5. To give an example from that book, Table 5.4 p 141 gives values for Li+ as 22 and 13-14 by tranference numbers, 3.5-7 and 7-21 by mobilities, 2-3 by conductivity, 5 by diffusion, 2.7 by compressibility, 5 by entropy and 3.4-5 by NMR. The point is, different properties are measured by the different techniques.

The current text is OK, though I still stand by the assertion that H9O4+ is a reasonably well characterised species. I think that the reference to Zavitas should be deleted as it is not definative. We need a better reference for the hydration of the proton in aqueous solution.

I found the paper to be fairly convincing, personally. The reason I liked the method was because it checked the freezing point depression constant. As such, unlike a lot of other methods it shouldn't have altered the structure of the liquid too much (like gas-phase tests would). I recognize that as water reaches freezing it develops a crystalline structure which is radically different from its liquid state. But freezing point depression seems like a pretty true to life method to check this. On the other hand, anything that alters the solution (like checking conductivity, gas phase etc) seems like you'd be destroying the sample as you made the measurement. I'm not quite clear on how one would use NMR for this though. My best guess is using computational methods to predict NMR spectra for lithium bound by a different number of water molecules. EagleFalconn (talk) 13:46, 8 August 2008 (UTC)

I question, what exactly is being measured? Solvation numbers based on colligative properties do not feature at all in Burgess and he also talks of "the unwise assumtions of splitting experimental values for salts into single ion components". As far as this article is concerned we need to find a review to cite, not this rather specialized paper. Petergans (talk) 18:51, 8 August 2008 (UTC)
Ths reference has been replaced by two others, based on spectroscopy.In principle each hydrated species has a unique spectrum so this technique is sound. Examples of the spectra can be seen at Fundamental aspects of proton accomodation by water (pdf). The use of HDO for these studies is a well-established means of simplifying the vibrational spectra as O-H and O-D stretching vibrations occur in distinct regions of the spectrum. Petergans (talk) 13:18, 9 August 2008 (UTC)
Good enough for me. EagleFalconn (talk) 17:39, 9 August 2008 (UTC)

## Equilibrium constant

There is something wrong with the final paragraph as "insensitive" directly contradicts the ionic strength dependence of pK. The ions of the ionic medium are supposed to be spectator ions. I don't see the point of including this paragraph, but I'll leave it to you lot to amend it or delete it. Petergans (talk) 09:12, 8 August 2008 (UTC)

The reason I inserted the paragraph initially was in response to the graph of the relative abundances of citrate ions at differing pHs. It seemed worthy of mentioning that by adding a strong acid like HCl you could decrease the pH without affecting the other aspects of the equilibrium, as I didn't feel that it was sufficiently clear with our current summary of the equilibrium constant. EagleFalconn (talk) 13:19, 8 August 2008 (UTC)

I think that what you are getting at is that a pK is determined by pH titration and that K does not vary during the titration. Maybe a brief description of the method would be better? Petergans (talk) 13:18, 9 August 2008 (UTC)
Added a brief section of determination of pK values. Does this cover the issue?Petergans (talk) 17:09, 10 August 2008 (UTC)
No, quite literally what I'm getting at is the need to establish the fact that the equilibrium constant does not change in the presence of other chemicals as long as there is no competition for a reaction. Its a non-obvious fact. EagleFalconn (talk) 01:05, 11 August 2008 (UTC)
OK, it's a good approximation, but strictly only true for a concentration quotient if the activity coefficient quotient, ${\displaystyle \Gamma }$, does not change, so some re-wording is needed. As a matter of fact, I'm working on a program to determine stability constants which uses SIT theory (not yet in WP) to calculate the individual ion activity coefficients, which can vary during a titration, and thus produce stability constants that are activity quotients. Petergans (talk) 08:30, 11 August 2008 (UTC)
I've rewritten, what do you think? EagleFalconn (talk) 12:54, 11 August 2008 (UTC)

OK! Petergans (talk) 16:35, 11 August 2008 (UTC)

## Tablulated pK values

I've added a table of values in AN and DMSO to the non-aqueous section. It has brought into focus the issue with aniline. The value of about 30 is the dissociation constant of aniline, clearly not obtained in water. pKb for aniline is 4.63. So, the table of typical values needs to be split into acids and bases. It also makes me wonder if the title is adequate since we make much of the pKa values of the acids conjugate to bases. I can't think of a snappy title that mentions bases also, at the moment.

I'm thinking of adding a little on hydrolysis reactions, with a particular mention of the ATP/ADP reaction.

ATP + H2O → ADP + PO4 + H+

All phosphate species are protonated at biological pH, so I've left off the protons and the charges for the moment. Petergans (talk) 17:09, 10 August 2008 (UTC)

It would, of course, be much easier to simply remove values that we find specious. I don't know that I find the ATP/ADP reaction particularly interesting. Is there any reason in particular it ties directly into pKa? EagleFalconn (talk) 01:14, 11 August 2008 (UTC)

It's marginal, as with metal ion hydrolysis, though this and other polyoxometallate ions are important in acid-base chemistry and there are lots of pK values in the literature. Some of the other stuff I added is also marginal, like superacids to mention one topic. I think we need to take a good look at the whole article and remove stuff that is not directly relevant to pK values. Petergans (talk) 08:30, 11 August 2008 (UTC)
I've looked at reorganizing/cleaning up the article a little bit. Heres what I've got in mind:
• Move the discussion about self ionization of water below polyprotic acids, above bases.
• Move superacids/superbases to the "Importance" section
• In importance, what is the significance of "pKa of an acid, HA, is related to the proton affinity and solvation (hydration) energy of A− in the gas phase." It feels like an out of place fact on its own. Is there a better option for placement?
• I'd like to move "Importance" below "Non-Aqueous Solutions" and above "pKa's of some common substances".
• Acidity of nonaqueous solutions needs to be generally reorganized to be a little more cohesive(I know what I mean by this, I'll take care of it if you agree).
• I'd like to use electrophillic aromatic substitution as the example for the nitronium ion instead of its reaction with water. I feel like its a little more compelling and more interesting of a reaction.
• Regarding the speciation section: What exactly is the purpose of this section? I feel like its a rather long aside...I'm not sure how much it really adds. Can we take the core content of this section and put it elsewhere? (EagleFalconn (talk) 14:15, 11 August 2008 (UTC))
Thoughts? EagleFalconn (talk) 13:16, 11 August 2008 (UTC)

Regarding your last point: I think that the article is becoming a bit long; according to my browser print preview function, it takes 18 printed pages. Wikipedia:Article size suggests that one consider splitting articles that get longer than 10 pages. This is just a rule of thumb, but I generally find it reasonable. Regardless of the specific page count, I think that this article is turning into a general introduction to acid-base equilibria, and not just acid dissociation constants. Perhaps some parts of the article, such as the speciation section, could be treated using summary style--"spin them off" to a separate article and just leave one paragraph here as a summary. I realize that I encouraged the expansion of the speciation section by suggesting that a diagram for a polyprotic acid be added, but now I realize that perhaps I erred on the side of comprehensiveness. The content and the diagram of course are still valuable and can be used in other articles even if they are removed from this one. --Itub (talk) 14:53, 11 August 2008 (UTC)

I agree with most of this. As a matter of fact I've done some revision of hydrolysis, Lewis acids and bases and Brønsted-Lowry acid-base theory while we have been developing this article, so as to be able to "hive off" chunks of detail, like metal ion hydrolysis.
Speciation is very important because it relates pH to pK. I'll see if it can be tidied up a bit. Details of the calculation are in Determination of equilibrium constants#Speciation calculations and none of that stuff is repeated here. I could envisage an article on equilibrium speciation, but it would have to include solids, liquids and gases in equilibrium, so that's not on, for now.
Overall length is not quite as bad as appears at first sight because of the tables which add to the length but do not fill the lines as text would. For me, the last table is a bit problematic; does it add anything of significance? Would it not be better to give a list of data sources? I don't see much else to cut out, so I suggest we don't worry about length and wait to hear if it is a problem when it goes up for FA. Petergans (talk) 16:35, 11 August 2008 (UTC)
I generally agree with the length argument, and hopefully some of the above cleanup will help with that. Using the Firefox extension Nuke Anything I removed the tables. Before removal, the printed HTML rendering came as 20 pages, with removing the tables it came in at 17. I'll also read through to see if I can splice out some redundancy (though I'm not sure there is any there).
I'll start inputting the cleanup I mentioned above.
I do like having the last table of sample pKas there. For anyone with a mild background in chemistry but needing an introduction, its useful to have it there to give a quantitative feel for something they might already have a qualitative understanding for. That said, it might be better to integrate that table into the full text somehow.

EagleFalconn (talk) 17:12, 11 August 2008 (UTC)

How about making it a floating table, somwhat like an image? --Rifleman 82 (talk) 17:23, 11 August 2008 (UTC)

I don't see how that would really save that much page/screen space. Would it be possible for you to put something together in a sandbox so we can get a visual example? The impression I get is that you're talking about Help:Table#Floating_table. EagleFalconn (talk) 17:31, 11 August 2008 (UTC)

Check out User:Rifleman_82/Sandbox2? I've removed the navbars at the right for now - how about turning them into navboxes at the bottom, which are the de facto standard in most articles.

I would also like to trim a few items from the box:

• Arsenic acid, chromic acid, hydrogen selenide are not exactly common; "chromic acid" is also somewhat ambiguous - H2CrO4 or H2Cr2O7?
• Acetic acid, boric acid, maleic acid, phosphoric acid are duplicated in another box

What do you think? --Rifleman 82 (talk) 18:08, 11 August 2008 (UTC)

I'm feeling a little crowded. I'd suggest giving the table wider berth by giving it some margins, but then we'd be cramping a lot of text into a little space. I agree with removing those entries though.. EagleFalconn (talk) 18:29, 11 August 2008 (UTC) Also, I'm fine with navboxes at the bottom of the article. EagleFalconn (talk) 18:33, 11 August 2008 (UTC)

## "AN" or "ACN"?

Just wondering - I usually see acetonitrile abbreviated "ACN", not "AN". Is this some sort of convention physical chemists prefer? --Rifleman 82 (talk) 16:48, 11 August 2008 (UTC)

I typically use ACN -- I would guess its a British convention as Petergans is from England. EagleFalconn (talk) 17:03, 11 August 2008 (UTC)

## Article Structure Changes

I've made the following major structural changes to the article.

• I'd like to see if theres a good place to move up the "Importance" section as I feel having an importance up front will help focus the reader on why they care.
• Struck the "Hydrogen ions in solution" subsection and spin it off into an article. I remember this got added initially as a request to clarify what a hydrogen ion was, but this is a bit much for our purposes. All we needed to say was Hydrogen Ion = Proton.
• Homoconjugation has been cut in half. Its an important point for non-aqueous solvents, but its not that important for this article. As the resident expert on it Peter, I'm going to leave this one to you.
• "Speciation" has been deleted and will be spun off as its own article. It has been given a place in "Importance"
• "Experimental Determination" goes below "Factors that determine relative strength" which is below "Non-Aqueous Solutions"

EagleFalconn (talk) 20:56, 11 August 2008 (UTC)

## Speciation diagrams

I've restored the diagrams, with reduced commentary, because they carry essential information much more effectively than text. Speciation is fundamental to the understanding of how buffer solutions relate to pK values. There was previously some duplication between equilibrium constant and monoprotic acid which has been eliminated, so the text is not that much longer.

Please delete the article speciation of ions; it is completely unsatisfactory outside the context in which the text was originally created.

Regarding AN and ACN, when a situation like this arises it is better that both abbreviations are avoided. MeCN or CH3CN would be acceptable. Am I right in thinking that ACN is used mainly by organic chemists? Petergans (talk) 19:00, 12 August 2008 (UTC)

I usually call it "acetonitrile" or MeCN written out. I see "ACN" very often on HPLC solvent reservoirs though. --Rifleman 82 (talk) 19:04, 12 August 2008 (UTC)
I concur with seeing ACN on HPLC resevoirs. My first real encounter with the solvent was working as a chromatographer, which would explain it. I concur with MeCN as it is as unique as CH3CN. However I hesitate to put chemical formulas in text -- is there a stated preference for using a name over the formula or even MeCN anywhere? I don't see anything particularly wrong with speciation of ions. Its definitely not the greatest article standing alone, but we can't have a wikilink that points to nothing. And besides, it doesn't have to start great. It'll get there eventually. (WP:IMPERFECT) EagleFalconn (talk) 19:14, 12 August 2008 (UTC)
I've ofter seen MeCN in the middle of text. It's short for methyl cyanide which is the IUPAC recommended name. Petergans (talk) 08:22, 13 August 2008 (UTC)

Wait, so is speciation not important now? EagleFalconn (talk) 19:23, 12 August 2008 (UTC)

There is a basic misunderstanding here. Speciation is essential for our article. What is the use of a pK value if not for calculating speciation? What I'm saying is, having restored the most relevant bits and integrated them into the text, there is no need for a separate section or article. The idea of hiving speciation off was misconceived. The baby was thrown out with the bathwater. Petergans (talk) 08:22, 13 August 2008 (UTC)
There is a middle ground. The speciation section of this article could perhaps be made a bit shorter, while the article on speciation of ions definitely has room for expansion. For starters, it could show the equations that are used for polyprotic acids, and it could have more than one example of a polyprotic acid: in particular, it is interesting to see the difference between acids with pKa's that are far from one another as opposed to close to one another. However, I would rename it to acid-base speciation; the current title is too general, because it "ion speciation" could include complex speciation, redox speciation, etc. --Itub (talk) 09:00, 13 August 2008 (UTC)
I just re-read the article and I think the speciation section as it is now fits very well. I don't think it needs to be shortened. However, the point that it is possible to write a more detailed article about speciation remains. --Itub (talk) 12:38, 13 August 2008 (UTC)
I am strongly opposed to the creation of an article acid-base speciation for various reasons. i) The topic is too narrow, as the same equations and procedures also apply to the speciation of coordination complexes. See Determination of equilibrium constants#Speciation calculations ii) The same equations can be made to apply to solid/solution equilibria also. The mathematics was described in the 60's with the publication of the program HALTAFALL. iii) Just look at the major software items available for speciation of equilibria in all phases.
EQS4WIN A powerful computer program originally developed for gas-phase equilibria but subsequently extended to general applications. Uses the Gibbs energy minimization approach.
CHEMEQLA comprehensive computer program for the calculation of thermodynamic equilibrium concentrations of species in homogeneous and heterogeneous systems. Many geochemical applications.
WinSGW A Windows version of the SOLGASWATER computer program. (In turn derived from HALTAFALL)
Visual MINTEQ A Windows version of MINTEQA2 (ver 4.0). MINTEQA2 is a chemical equilibrium model for the calculation of metal speciation, solubility equilibria etc. for natural waters.
MINEQL+ A chemical equilibrium modeling system for aqueous systems. Handles a wide range of pH, redox, solubility and sorption scenarios.
In view of these, limiting an article to acid-base speciation makes no sense to me. A more general article on equilibrium speciation is certainly a possibility. Petergans (talk) 13:31, 13 August 2008 (UTC)
All right, I'm not strongly in favor of the acid-base speciation article, but I would suggest considering the possibility that, although you are correct that in the real world one has to consider all relevant equilibria (and this is what the software you mention does), perhaps an article exemplifying acid-base as a limiting case could be useful for pedagogical reasons. It can be simpler to understand than the general case, and if you write an article on the general case, it could well end up being too long. But anyway, since I'm not going to write either of those articles myself, take this just as a suggestion. --Itub (talk) 13:45, 13 August 2008 (UTC)
Whatever you decide is fine. I just don't want content to be lost. EagleFalconn (talk) 14:09, 13 August 2008 (UTC)

## Another round of editing

I've completed another round of editing for those nagging style details (spacing, spelling, grammar, capitalization, punctuation, typesetting, etc.), as well as some changes of phrasing. The content looks very good (I think it flows better than the last time I went through it), and I think the article is almost ready for FAC. I only see two issues remaining:

• In my experience, some FA reviewers tend to be list- and bullet-phobic. They won't like the way the Importance section is laid out. Perhaps it can be turned into regular paragraphs? (Maybe with subheadings, but I'm not sure about that, because most of the subsections would be only one paragraph long.)
• More references. Now it has enough references so that no one should oppose just by counting the references at the end (it happens!), but still, some people practically demand at least one reference per paragraph. At least one reference per section is almost certainly required. Currently there are no references for the Mixed solvents section, and no references for the Experimental determination section, other than one about the specific case of NMR. Other places where it would be a good idea to add references:
• One per application in the Importance section.
• The explanations for the acidity or basicity of proton sponge and maleic acid.
• The "bare proton" statement

One final comment: the article had an inconsistent mix of American and British spellings. I tried changing everything to American because it seemed to be dominant, but I don't care either way as long as it's consistent. --Itub (talk) 13:40, 13 August 2008 (UTC)

Regarding the list and bullet-phobia, I would think that the current format of the importance section is probably the best way to do it. In my perspective, paragraphs are for ideas that are logically connected to each other. Here the ideas are only connected by the fact that they involve pKa's. By not shoehorning it into paragraph form, we're keeping it concise and readable.
I'll start digging up more references. Especially the bare proton thing. EagleFalconn (talk) 14:09, 13 August 2008 (UTC)
• Good work, Ivan!
• Ive added some more references, including one for Experimental determination.References for mixed solvents are in the pipeline. Should an instrument manufacturer, for example, be referenced?.
• There is some inconsistency regarding references in the Lead-in and Importance sections at the moment. I would rather put all references in the Importance section and not to have them in both sections. What is the preferred option?
• It is a matter for concern that there are references to so many text books: Miessler, Shriver & Atkins, Brown, Lemay & Bursten, Greenwood & Earnshaw, Atkins & De Paula, Loudon & Marc, Housecroft & Sharpe, March & Smith, Brown, Lemay & Bursten ( second time). These are tertiary sources and often do not give references. It would be preferable to cite primary or secondary sources (reviews with references), rather than leaving it to the reader to hunt out the original publications. At least, that's what is done in ACS and other journals. Petergans (talk) 12:46, 14 August 2008 (UTC)
1) I don't think it's common practice to mention manufacturers, unless it is for something truly unique that's made by only one or two companies in the world. 2) References are normally not required in the lead section, because the lead is supposed to be a summary and everything mentioned there should be explained (and referenced) in detail later in the article. 3) Reviews and monographs are ideal, but textbooks are generally considered acceptable in Wikipedia, especially for basic stuff such as the definition of the equilibrium constant. However, I wouldn't recommend using textbooks as references for data.
These are just general comments because I still haven't looked at the references in detail. --Itub (talk) 13:02, 14 August 2008 (UTC)
I spent a good part of my downtime yesterday trying to dig up a reference for the bare proton thing. I can find plenty of references referring to the proton as a very hard acid, I can find references speaking to the stability of the hydronium ion versus water + H+ (computational studies). But I can't really find anything directly relating to the reactivity of the proton regarding the speed of its reactions (kinetics). Would it be enough to cite a paper calling electron pairs a very hard base and proton a very hard acid? Does it even make sense to call an electron pair a base?
Also, to assuage some of your fears about the textbooks. I can tell you that Brown, LeMay, Burnsten is one of the most widely used and authoritative general chemistry books in the United States. I've seen a lot of gen chem books in my job as a tutor, and it is the best I've ever seen. Same story with Loudon. EagleFalconn (talk) 13:38, 14 August 2008 (UTC)
The reference have been moved from Lead-in to Importance. I tried to see where I could get a copy of Brown, LeMay, Burnsten. It turned out to be very difficult. Leeds Uni library has one copy of the 2nd edition! Trawling the web sites revealed a real mess of editions of the main book and "international" editions. The current main edition seems to be 9th., but 11th. is cited in the article. This problem of editions is common to all popular text-books, which is another reason to avoid citing them!. Petergans (talk) 18:20, 14 August 2008 (UTC)
The international edition of BLB is exactly the same as the United States edition, except it comes in paperback. The current edition is, as you say, the 11th. I don't know how much has changed since the 10th, but to me it looked like most of the acid/base material was the same, and I used the 9th edition in highschool. I'm surprised Leeds only has a copy of the 2nd edition, what general chemistry books are popular there? EagleFalconn (talk) 02:21, 15 August 2008 (UTC)
General chemistry is not taught in English Universities. Our students have completed a 2-year course in "A" level chemistry before they come to us. The syllabus for that course is defined and there is a range of text-books designed for teaching to that syllabus. General chemistry books designed for US students contain too much off-syllabus material to be really useful. Amazon UK only stocks Chemistry: The Central Science by Theodore E. Brown, H. Eugene LeMay, Bruce E. Bursten, and Catherine Murphy (Paperback - 1 Feb 2008). It does not state what edition that is. Blackwells bookstore has Chemistry The Central Science Theodore Brown, H.Eugene LeMay, Bruce E. Bursten, Catherine Murphy, Patrick Woodward. That's what I meant by " a mess of editions". The book may well be of first class quality, but from an international point of view, it does not look like a good source to cite in WP.Petergans (talk) 08:41, 15 August 2008 (UTC)
They're the same edition. For years the authors have only been Brown, LeMay and Bursten but Brown is an emeritus professor and has taken on more of an editorial role in the book writing lately, so they've added on two more authors (Murphy and Woodward). Woodward isn't on the cover, which is probably why Amazon doesn't mention him, but he's on the inside. I agree that its probably not a good textbook to cite from an international perspective. But finding a primary or secondary source for that seems equally futile. It might be possible to find one, but its going to be from a VERY old paper -- I doubt you'll see much of that in the primary literature. And the problem with old papers, and an issue I have with primary and secondary sources in general, is that they're not readily accessable to the fact-checking public. EagleFalconn (talk) 16:29, 15 August 2008 (UTC)

## Table of values for common substances

1. references at the head of the table
2. removed aniline again!
3. removed compounds listed in the thermodynamics table, but added link to that table.
4. revised adenine and codeine which are bases, not acids.

I am concerned that no information about ionic strength is given in this table. Petergans (talk) 10:13, 15 August 2008 (UTC)

Well, as we say in the introduction, equilibrium constants are usually determined at concentrations high enough that the activity ratio is 1. As such, I've never in my chemical career yet run into a table of ionic strengths. EagleFalconn (talk) 21:08, 15 August 2008 (UTC)

I suggest you read the IUPAC guidelines for publishing equilibrium constants. In the thermodynamics tables the values are stated to be for I=0. If the sources for the final table contain information on I, it would be sufficient to quote them in the header. The point is, a reader might find a different pK value somewhere else because it relates to a different ionic strength. In elementary texts ionic strength and activity considerations are usually completely ignored, but in WP we have to be more rigorous. Petergans (talk) 09:07, 16 August 2008 (UTC)
I agree, I was simply pointing out that they're not broadly accessable. The resources I've identified so far are the National Physical Laboratory and an article in the Iranian Journal of Science and Technology, which I don't have access to. Taghikhani, V.; Modarress, H.; Vera, J. H. Activity coefficients of individual ions. Iranian Journal of Science and Technology (2002), 26(B2), 299-306.EagleFalconn (talk) 18:46, 16 August 2008 (UTC)
That's not what I meant. When a pK value is given in a table, the temperature and ionic strength at which the value was obtained should accompany it. We have the temperature at the head of the table. The sources I meant were Lange's handbook and Knovel, where the values came from. Do they give the ionic strengths? If not, we might have to say "at various ionic strengths", but that would not be very satisfactory. 0.1M is the most commonly used, but we can't assume that this applies to all. My database does give ionic strength with the values, but only lists organic ligands if they form metal complexes, so I can't check all of them. Petergans (talk) 10:09, 17 August 2008 (UTC)
Aren't pK values for reference purposes extrapolated to I=0? They ought to be (but I wouldn't bet on it ;) Physchim62 (talk) 14:54, 19 August 2008 (UTC)
Ah. Lange's extracts to I=0. I can't find anything specific from Knovel, but if what Physchim62 says its true, it'd be a good guess to assume it does. EagleFalconn (talk) 05:39, 20 August 2008 (UTC)
In that case we should stick to values given by Lange and Goldberg. If Knovel does not state I=0 explicitly that is a fundamental flaw. Petergans (talk) 08:04, 20 August 2008 (UTC)

## Minor revision

The article has been "refereed". Go here for comments. I have done some minor revision in the light of these comments, bearing in mind that the author is a specialist in pK values in non-aqueous solvents. He has offered to write short paragraphs on organic synthesis and liquid chromatography. Should we take him up on this offer? Petergans (talk) 14:05, 18 August 2008 (UTC)

It can't hurt. EagleFalconn (talk) 05:39, 20 August 2008 (UTC)

## Go for it

The article appears to be stable. Why not go for FA NOW? Petergans (talk) 10:10, 7 October 2008 (UTC)

Sounds good. I'm still a bit afraid that some people will complain that there are some paragraphs with no references, but perhaps I'm being overly paranoid and the best way to find out is to try. --Itub (talk) 05:29, 8 October 2008 (UTC)

I don't think this article has a chance for Featured Article status as it is right now. Just two things that I can note right off the back. It does not have a history section (which of course the usage of the acid disassociation would), and it does not explaining how pKa=pH at the half-equivalence point outside of the Henderson-Hasselbach equation. From my experience in College Chemistry Lab, this is critical for experimental determination of pKa values (which is then used to find Ka) in monoprotic acids, so the fact that it gets one sentence will not cut it.--Jorfer (talk) 13:17, 8 October 2008 (UTC)

I tried to give the following so that students can better understand how pKa=pH relates directly to the definition of Ka and not just the Henderson-Hasselbach equation: The point at which 50% neutralization of the acid occurs is called the half-equivalence point.[1] At this point since

${\displaystyle K_{a}=\mathrm {\frac {[A^{-}][H^{+}]}{[HA]}} }$

and ${\displaystyle [A^{-}]=[HA]}$, the definition of the equilibrium constant can be rendered

${\displaystyle K_{a}=\mathrm {\frac {[A^{-}][H^{+}]}{[A^{-}]}} }$

which cancels the [A-] out and leaves ${\displaystyle K_{a}=[H^{+}]}$. Since, pKa = -log10Ka[2] and pH = -log[H+][3], pKa = pH at the half-equiavalence point.--Jorfer (talk) 13:19, 8 October 2008 (UTC)

User Jorfer has not apparently understood that this is the same derivation as in the article which states:
After rearranging the expression defining Ka, and putting pH = −log10[H+], one obtains
pH = pKa – log ( [AH]/[A−] )

The only difference is that logarithms are taken at the beginning, not the end. This formulation is more useful because it allows an easy definition of the buffer range as well as the half neutralisation point.
Regarding history, it is there in the definitions section. Petergans (talk) 08:33, 9 October 2008 (UTC)
I realize that Henderson-Hasselbach is taken directly from the definition, but I feel that this needs to be clarified (if not simply stated). Also, my mistake, the definition does cover a brief history, just not in a historic style. This section could be buffed up though with a history of determining the Ka of substances experimentally (i.e. the techniques used, notable contributors, etc.).--Jorfer (talk) 16:41, 9 October 2008 (UTC)