Talk:pH/Archive 3

Archive 1

Archive 2

Archive 3

Molar link

The link from the term "molar" in the introduction points to the disambiguation page. The context seems to indicate that "molar (concentration)" is meant. Could an established editor re-link this please?

Msramming (talk) 02:26, 18 December 2009 (UTC)

Done. Vsmith (talk) 02:38, 18 December 2009 (UTC)

Why is this article semi-protected?

I didn't see a discussion in the archives (though I might have missed it). What is the reason for the protection, and how long will it last? 71.224.206.164 (talk) 03:45, 3 February 2010 (UTC)

It was semi-protected due to excessive vandalism in Nov. 2008. I've just now unprotected, try it for a while. Vsmith (talk) 04:42, 3 February 2010 (UTC)

Thanks. 71.224.206.164 (talk) 05:08, 4 February 2010 (UTC)

Then again... why is this article such a target? It might have to do with pH being such a common concept in secondary school chemistry curricula. Maybe the introduction could be geared a little more towards the non-technical reader? 71.224.206.164 (talk) 05:34, 4 February 2010 (UTC)

ph value of hair colours —Preceding unsigned comment added by 109.79.24.57 (talk) 15:58, 22 March 2010 (UTC)

pH typeset as math

Should pH by typeset as math? it looks different (pH vs $pH$) and according to at least Jens Norby it is a mathematical symbol, which should be typeset as math. El sjaako (talk) 13:02, 8 April 2010 (UTC)

pH of "pure" water at 50 degrees C

If the water absorbs carbon dioxide from the air, then it is no longer pure water, is it? —Preceding unsigned comment added by 144.30.74.164 (talk) 19:36, 18 April 2010 (UTC)

pH scale and temperature

Although it is mentioned in the article that the 0-14 range and neutral pH=7 apply at 25 C, I think it might be better to write it more explicitly with more math. At the point where the self-ionization of water is mentioned I think it should be explicitly said that the constant for the equilibrium is Kw=[H+][OH-], when the solution is neutral [H+]=[OH-], thus Kw=[H+]^2 which means that for a neutral solution pH=(1/2)pKw. Similarly, the upper limit of the scale is usually considered as [OH-]= 1 M, thus Kw=[H+] and pH=pKw. Increasing temperature favours the self-ionization, increasing the value of Kw (or decreasing the pKw) and thus decreasing the pH value of a neutral solution and the nominal upper limit of the scale. —Preceding unsigned comment added by 79.107.227.200 (talk) 15:41, 14 July 2010 (UTC)

Potential of Hydrogen

Could this be mentioned somewhere, perhaps in the lead? I wondered what pH stood for, and only found out while playing trivia. -- 124.171.236.204 (talk) 08:28, 2 October 2010 (UTC)

It's in the history section. Vsmith (talk) 14:39, 2 October 2010 (UTC)

Oh, should have seen that before. Sorry! And thanks. -- 124.171.236.204 (talk) 18:06, 2 October 2010 (UTC)

Acidosis

I would suggest the following changes to this sentence, which currently reads: "The most common disorder in acid-base homeostasis is acidosis, which means an acid overload in the body, generally defined by pH falling below 7.35." Since the table to its right lists several systems in the body that apparently have ideal pH levels below 7.35, I think a noun phrase needs to be inserted to clarify exactly *what* it is that falls below 7.35. What system, and how is it measured? Also, insert [citation needed] after this sentence. So, I propose it should read: "The most common disorder in acid-base homeostasis is acidosis, which means an acid overload in the body, generally defined by the pH of [specific body system] falling below 7.35, measured by a [blood test, spinal tap, urine test, what test?] that returns a pH value below [specific number], whereas its normal range is [specific numbers]. [citation needed]"

The reason for putting these specifics in is to boost the medical validity of this statement, which as it stands, is inconsistent with the table to the immediate right of the sentence. Furthermore, many popular books on acidosis recommend a urine test for acidosis, which, if the test comes back reading acidic levels, is supposed to mean the person has acidosis. Guess what? Any urine test will come back with acidic levels, because the pH of urine is about 6. So, putting some specifics in here and saying what doctors actually do to test for acidosis would make this section more credible. If specific medical information about valid tests for acidosis is not forthcoming, then I would recommend removing this sentence, and the figure on acidosis.

The acidosis figure's citation to Medline Plus contradicts the claims made in the figure: The Medline Plus citation specifically states: "Most symptoms are caused by the underlying disease or condition that is causing the metabolic acidosis." The citations for this figure do not include any medical references to peer-reviewed articles. The symptoms listed are vague, overlapping considerably with those of flu, general stress, postconcussion syndrome, anxiety disorder, post-traumatic stress disorder, and the common cold. I'm not convinced that the cited sources for the information in this figure are really up to the standards of Wikipedia articles. Finding that one of the listed citations directly contradicts what the figure says is truly problematic. Drvestone (talk) 17:28, 14 November 2010 (UTC)

pH levels of juices

What are the pH levels of orange juice, lemon juice, and apple juice? —Preceding unsigned comment added by 69.138.69.0 (talk) 00:50, 17 January 2010 (UTC)

Go read Orange juice, Lemon juice, and Apple juice. -Halidecyphon (talk) 23:45, 6 September 2010 (UTC)

Can we not create a list of pH values of different foods and drinks? I believe it would be highly valuable. Rui ''Gabriel'' Correia (talk) 12:44, 17 February 2011 (UTC)

pH of plants/ red wine

Hi. Should "red wine" not read "red grape" in the setence that follows? "pH-dependent plant pigments that can be used as pH indicators occur in many plants, including hibiscus, marigold, red cabbage (anthocyanin), and red wine". Red wine is not a plant, so perhaps it should read "pH indicators occur in many plants and plant products". Rui ''Gabriel'' Correia (talk) 12:50, 17 February 2011 (UTC)

pH calculation inaccuracy

pH = -log([strong acid]) does work for small amounts of strong acids. For instance 10^-8M HCl in water will only change the pH to about 6.89, because the change is not so large compared to equilibrium constant of water. —Preceding unsigned comment added by 109.65.22.196 (talk) 13:26, 18 January 2010 (UTC)

The calculation section is completely fubar. I'm about to do a complete rewrite. Klortho (talk) 04:47, 13 March 2011 (UTC)

As I mentioned I would, I completely rewrote [| this section]. I didn't quite finish my to-do list, but I'm afraid that it is already too long and too detailed. The subsections say "... acids and bases", but I only addressed acids. The calculations I gave are all very elementary, and I didn't try to cover poly-protic acids or any of the hundred other complications. I'm also worried that it's too much of a tutorial and not encyclopedic enough. I'm new at this, so suggestions are very welcome. Klortho (talk) 23:52, 13 March 2011 (UTC)

PH and Temperature

I am not a chemist but I would like to know why the measures are taken at 25ºC. What is the relation between the temperature and the PH value of the same substance, say, orange juice or even water? There must be some definite relationship between the two. — Preceding unsigned comment added by R.Kurylski (talk • contribs) 18:12, 9 April 2011 (UTC)

Is pH applicable to non-water solutions?

e.g., can pure ethanol have a pH? 75.4.194.121 (talk) 09:15, 16 January 2011 (UTC)

Of course, just that the interval for ethanol is not 0-14. Every solvent has its own pH interval due to autoprotolysis.-86.125.150.173 (talk) 12:20, 5 May 2011 (UTC)

pOH is a measure of basicity, not alkalinity

In the section http://en.wikipedia.org/wiki/PH#pOH

"pOH is sometimes used as a measure of the concentration of hydroxide ions, OH−, or alkalinity." should be

"pOH is sometimes used as a measure of the concentration of hydroxide ions, OH−, or basicity."

The pages http://en.wikipedia.org/wiki/Base_(chemistry) and http://en.wikipedia.org/wiki/Alkalinity are correct in this matter and show why the statement as written is incorrect.

The term alkalinity is frequently incorrectly used as a synonym for basicity. For an outside confirmation of the difference, please read http://www.chem.usu.edu/~sbialkow/Classes/3650/Alkalinity/Alkalinity.html "Alkalinity is the defined as a body of water’s ability to react with the acidic proton(more correctly, cation). The alkalinity is like buffer capacity in that higher alkalinity is associated with a body of water’s ability to "soak up" proton(again, cation) without altering the pH."

69.68.114.179 (talk) 04:40, 9 May 2011 (UTC)

Extremes

it would be nice to add info about extreme pH-s. low end is something like SF5-HF ? is this outdated? what is highest? CsOH? hard to find such information. —Preceding unsigned comment added by 178.21.49.118 (talk) 08:42, 8 October 2010 (UTC)

Yeah, there is little mention about how the range of 0-14 is only due to the dissociation limits of water and Hydronium. There should be more about the pH of non-aqueous solutions. SbF5-HF is the lowest, to the best of my knowledge. Around -25? The highest pKa compound is an ethyl anion (in DMSO) with pKa of about 50. —Preceding unsigned comment added by 153.90.187.67 (talk) 18:44, 13 May 2011 (UTC)

Too technical

As someone mentioned above, pH is a common middle school chemistry topic. But the lead is written at a level that this scientist and engineer must read very carefully, reaching into the dark recesses of seldom-used vocabulary, reading many linked Wikipedia pages, to decipher it. The rest of the article follows suit.

I'm not suggesting that information be removed from the article or that it should be dumbed down, but the concepts need to be presented in a way that can be easily understood by the entire audience—which includes 8th grade science students, high school dropouts trying to figure out how to care for a fish tank, and retirees taking a cooking class, in addition to the chemistry professors it's currently written for. Janus303 (talk) 11:34, 23 April 2011 (UTC)

Yes, but Wikipedia is not a textbook. Articles discussing acids and bases have been repeatedly over-written by well-meaning people who want to add qualitative lists, mnemonics or other "learn-by-heart" material to the article. This is harmful to the article, being somewhat similar to ideas such as "six strong acids" (there are more). That being said, there is no substitute for explaining clearly; articles covering fundamental topics often get very technical definitions for no good reason in the lede. --vuo (talk) 23:05, 5 May 2011 (UTC)

I'm a biochemistry masters student with a decent GPA, and I hate this article. It forays off into great detail about derivation, and gives a very, very poor description of concept. 173.120.63.219 (talk) 22:16, 5 November 2011 (UTC)Ubiquitousnewt

I also suggest simplifying this article. Although Wikipedia is not a textbook, neither should it be an obscure text of arcane wizardry. I'm not suggesting everything be diluted to include explanations for any technical reference, but as the article is at the moment, it is unreadable for all but those who already thoroughly understand not only the concept, but much higher degrees of science and mathematics in general. The whole point of Wikipedia is to allow for the spread of knowledge, but articles like this simply are impossible to obtain anything new from, as they assume you're a bioengineer (or similar). Anyone capable of understanding this article without combing through pages and pages of other articles likely wouldn't need to reference this page. The second sentence is already talking about logarithms, molar concentrations, and only makes more assumptions exponentially as the article continues on. In short, this article feels like a very large section of another article, due to the huge amount of assumptions and small amount of explanations given. I can understand leaving articles for obscure hypothetical sciences (such as various elements of Quantum Physics, temporal mechanics, etc) in largely technical terms, since there's simply no way to start learning their respective areas of science without starting lower. The thing with "pH" however is that the concept can easily be conveyed in much easier to understand terms without degrading it's use for those already familiar with the concepts. LiamSP (talk) 00:46, 28 February 2012 (UTC)

Wow! activity is always < concentration but activity equals concentration times a coefficient which may be > 1. Wow!

Somebody needs to get their act together in Definition section. For concentrated solutions, if activity coefficient is greater than one then the activity is greater than one. Or am I missing something. Wikipedia is really going down hill. Wonder why?71.31.149.105 (talk) 05:02, 25 March 2012 (UTC)

Major revision

The article has been extensively revised to bring it up to encyclopedia standard. I did this in my sandbox, so the most recent (presentational) edits may have been reverted. The section on applications has been moved nearer to the top of the article, but it is still rather weak, considering the importance of the topic. Some relatively trivial material has been removed. I hope that the balance is now about right. Petergans (talk) 10:48, 3 June 2012 (UTC)

Thanks for your extensive efforts. The introduction is still too technical, mentioning activity and solvated hydrogen ions too soon. The first sentence should be really simple and get across the key point that pH is a scale for the acidity of solutions. Solutions with pH less than 7 are not "said to be acidic", they are acidic. When I have more time I will help fix these issues. --Ben (talk) 11:41, 3 June 2012 (UTC)

Is it possible to rename the article "pH"? Petergans (talk) 09:42, 4 June 2012 (UTC)

I did the best I could by making the title display as pH. Wikipedia:Page name#Problematic names and Wikipedia:Naming conventions (technical restrictions)#Lower case first letter point out that it is impossible for the article title to start with a lowercase letter. However, Template:lowercase title renders the title as pH rather than PH. I have made this change. --Ben (talk) 22:28, 4 June 2012 (UTC)

Converting Temperature to degrees F.

I find it quite annoying that anytime a temperature is mentioned in degrees C it is shown in F in parenthesis. Most of the world uses C, so the constant "25C(77F)" again and again is very annoying. It should be fine to mention it once but not absolutely every time. — Preceding unsigned comment added by 173.77.88.21 (talk) 00:34, 17 April 2012 (UTC)

Unfortunately there are pockets of resistance in the USA. If you delete the references to Farenheit, some American will either revert it or (more likely) change all the temperatures to °F. DieSwartzPunkt (talk) 17:14, 7 July 2012 (UTC)

Thanks for this comment. I believe that all scientists use Celsius, but some engineers still use Fahrenheit. I'm keeping a watch on this article, so I'll deal with any further changes if and when they occur. Petergans (talk) 16:19, 9 July 2012 (UTC)

Whilst you are right about scientists, most engineers (and indeed the man in the street) in the US are still resolutely imperial. Wikipedia has to be accessible to general readership. DieSwartzPunkt (talk) 17:45, 9 July 2012 (UTC)

My ideal solution to this issue would be a "macro", activated by a mouse-over event, such that the conversion would appear automatically. In the case of radio-isotopes I used the correct atomic symbols (which the layman would not understand) linked to an article on the isotope. For example, ¹¹C decays by positron emission with a half-life of ca. 20 min. As we agree on use of °C by scientists, I suggest that °F should be avoided in articles of primarily scientic interest. In fact in this article the issue of temperature is peripheral anyway. Petergans (talk) 12:32, 10 July 2012 (UTC)

Further revision

Hi, I see you did a major rewrite of the calculations section. I agree that there was too much detail before, and think it's appropriate that you replaced a lot of the details with a link. However, one of the things that I tried to address in rewriting this section last year (see [[#pH_calculation_inaccuracy|above) was that it was way too technical. I think it's now got that problem again. Perhaps we could work together to bring it down to earth? For starters, do you have references for these calculations and terms (the article needs those anyway)? Thanks! Klortho (talk) 02:33, 13 August 2012 (UTC)

Also, I have to say, I wish you had done an edit summary when you did this edit; it would have made it easier for me to find. Klortho (talk) 02:43, 13 August 2012 (UTC)

The calculations and terms are discussed in most text-books on analytical chemistry. It's very old stuff. Bates, reference 1, is definitive (I have a personal copy). Reference 2 is available, free of charge, as a pdf file.Petergans (talk) 09:08, 13 August 2012 (UTC)

Please define [X]

Please define somewhere the meaning of [X] where X is anything, or provide a link to an article which defines it. If its in the article, its well hidden, I cannot find it. The concentration article hides it pretty well too. It should be defined at the first mention. I suppose it's moles of X divided by total moles? PAR (talk) 05:21, 4 October 2012 (UTC)

The use of square brackets is a convention in chemistry, meaning the "concentration" of the substance symbolised inside the brackets, without specifying the concentration units. It's been in universal use for I don't know how long, at least 50 years. A definition is in the first line of the lead: p[H] is a measure of the hydrogen ion concentration. Later, you will see that "p" stands for "minus the lograrithm of". Is this not clear enough? Petergans (talk) 07:53, 5 October 2012 (UTC)

pH: explanation of the term

It should be noted that the term 'pH' derives from 'potentia hydrogenii' (Latin for 'power of Hydrogen')

Elikrieg (talk) 14:45, 2 February 2010 (UTC)

Hi Elikrieg. Did you read the history section at the top of the article? It mentions both this definition and a number of others. Is there something missing? --PLUMBAGO 16:33, 2 February 2010 (UTC)

Hi Plumbago, the term potentia hydrogenii is not mentioned so far. One can put it together with 'pondus hydrogenii' (weight of hydrogen) which is mentioned in the history section. Anyways, the article is not locked any more. Elikrieg (talk) 13:48, 3 February 2010 (UTC)

Why does the introduction state that pH stands for Potential Hydrogen when the History section makes it clear that nobody knows what it stands for? 71.48.131.93 (talk) 17:14, 18 May 2012 (UTC)

I don't think 'p' stands for 'power', since a smaller pH value means a high concentration of H^+. It is the negative of power. Biohuang (talk) 07:41, 19 October 2012 (UTC)

hydronium != (solvated) hydrogen ion

Why is the link above the "(solvated) hydrogen ion" pointing at hydronium? Is it really the hydronium also in non-water solutions? — Preceding unsigned comment added by MarekMatejak (talk • contribs) 19:00, 3 April 2013 (UTC)

pH of concentrated liquid acids - inter-solvent scales

A supposedly trivial example of a situation like the pH of a solution of say nitric or sulfuric acid having a mass fraction of 0.5, would be beneficial to be included in article. What is the value of pH in this case?--188.26.22.131 (talk) 09:35, 19 August 2013 (UTC)

0-14?!?!

I suggest that someone remove all references to the scale being from 0 to 14. The page should even have a section explaining that negative numbers or numbers above 14 are just fine. — Preceding unsigned comment added by Bramblez (talk • contribs) 16:28, 8 February 2011 (UTC)

I second this suggestion. It is (relatively) easy to show that a 10-molar pH of a strong acid (e.g., HCl, neglecting activity effects) has a pH = - log₁₀ 10 = -1, and a 10-molar pH of a strong base (e.g., NaOH) has a pH of 15. (Trasmuss (talk) 17:58, 16 December 2011 (UTC))

Though an old discussion, I checked the article as of the date of the last comment, and nowhere did it claim a limit on pH of 0-14. DieSwartzPunkt (talk) 11:09, 10 July 2012 (UTC)

Although 0-14 is not mentioned, lot of people have this misconception. Hence, it is good to include a little about negative pH and pH > 14.Gband (talk) 06:14, 6 December 2013 (UTC)

suggestion--more examples

Please add a list of things with their average ph (and usual max and mins)--tap water, lakes, rivers, also in the seawater section discuss the variability of ph in different locations--for example the max and min ph for a year in some location where such things are recorded--such as Monterey Bay. --reader — Preceding unsigned comment added by G. Blaine (talk • contribs) 18:57, 1 October 2012 (UTC)

[[ ]] — Preceding unsigned comment added by 115.242.176.163 (talk) 09:42, 8 February 2014 (UTC)

pH is retarded.

Multiple reasons. Moles have no physical significance. Base 10 has no physical significance. In general you want your argument to exponents or logarithms to be unitless otherwise you end up with hideous units like log(particles/mole) instead of 1. The obvious unit to use is ln(parts H+/all parts) which is unitless and calc friendly.-Craig Pemberton 07:45, 22 December 2009 (UTC)

pH is dimensionless because it's a logarithm of a dimensionless quantity called activity. (see the very first sentence of PH#Definitions) --Cubbi (talk) 18:51, 22 December 2009 (UTC)

If pH 1 is equal to 602214150000000000000000 active hydrogen ions per litre, how can it be a dimensionless quantity? Åkebråke (talk) 19:22, 22 December 2009 (UTC)

Because that's incorrect. pH is defined as the negative logarithm of the *activity*, not the concentration. While activity in a solution can generally be approximated as being equal to concentration in moles per liter, that's not the definition and technically you get the activity by dividing the concentration with a reference value of 1 mol/l, which makes the resulting value dimensionless. - Alltat (talk) 16:53, 19 May 2014 (UTC)

It is dimensionless because activity is defined as the concentration relative to standard values (which for aqueous solutions is 1M) multiplied to its dimensionless activity coefficient ($\gamma$). Since it is a ratio, the units cancel.

$a_{H^{+}}=\gamma {\frac {[H^{+}\;in\;soln]}{1M}}$

As a result, activity is dimensionless. — Preceding unsigned comment added by 155.247.96.179 (talk) 19:35, 5 October 2011 (UTC)

Dimensions mol /dm -3

Please note the dimensions under 'applications' are mixed up. It is either mol / dm3 as in mol / liter, or it is mol dm-3. Mol /dm-3 is bogus. — Preceding unsigned comment added by 195.240.45.231 (talk) 18:37, 18 April 2013 (UTC) non — Preceding unsigned comment added by 206.41.88.119 (talk) 19:14, 20 May 2014 (UTC)

Calculation of the Ka value

For example:

Ka(H2O) = [OH−
]×[H+
]÷[H2O]
        = (Density(OH−
)÷Molar mass(OH−
))×(Density(H+
)÷Molar mass(H+
))÷(Density(H2O)÷Molar mass(H2O))
        ≈ (?g/L÷17.01g/mol)×(?g/L÷1.01g/mol)÷(999.97g/L÷18.01g/mol)
        ≈ ?mol/L×?mol/L÷55.52mol/L

But how to get the Density(OH⁻
) and Density(H⁺
)? Or is it possible to get the [OH⁻
] and [H⁺
] directly?

Thanks. 123.119.16.126 (talk) 13:39, 27 May 2014 (UTC)

User:Dirac66 answered at Talk:Acid dissociation constant. DMacks (talk) 18:50, 28 May 2014 (UTC)

hello I d like to know how many drops of ph+ I have to put in 10 litres of water to became 5.5 thank you — Preceding unsigned comment added by 37.116.130.168 (talk) 13:14, 30 July 2014 (UTC)

Swimming pools and spas

Someone ought to add information about pH in swimming pools and spas, since pH is very important in the upkeep of swimming pool and spa water. The "proper" pH for a pool is said to be 7.6 (with an acceptable range of 7.2-7.8), 7.6 in 60 degree F waters and 7.3 in 80 degree F waters, between 7.2 and 7.6, and 7.2, with an acceptable range of between 7.0 and 7.6. Different reasons are sometimes given, although not always: I noticed two separate pieces here claiming different pHs for the human eye (one says 7.2 and the other says 7.6), and other sources give calcium carbonate production and chlorine sanitation effectiveness as reasons for an ideal pH. Can someone come up with a reasonable account of what a "good" pH is for a swimming pool and spa, and why? — Rickyrab | Talk 04:20, 30 August 2009 (UTC)

I found myself having to enter a space for the ezine articles.com site because it was on a Wikipedia global blacklist. While I appreciate the need to protect against spam, this particular reference to that website was warranted because I was discussing various sources as to proper pool pH, and several of those sources are commercial entities. — Rickyrab | Talk 04:29, 30 August 2009 (UTC)

Pool maintenance is irrelevant to this article. Such information would be better in an article on swimming pools, or even better in a wikiHow on swimming pool maintenance. To discuss the pH in pools you need to discuss sanitation and lots of ions that are irrelevant to an encyclopedia article about pH. -Halidecyphon (talk) 23:42, 6 September 2010 (UTC) chris thomas kochu

The ideal range of pH for a swimming pool at least ought to be measured. This is an important application of the scale. PoolGuy7.5pH (talk) — Preceding undated comment added 17:40, 1 August 2014 (UTC)

Wrong Values in pH for Gastric Acid.

normal pH from Gastric Acid varies. from 4.5 to 1.5. but its never 1 unless its a patology

177.229.215.29 (talk) 01:26, 18 August 2014 (UTC)

No mention of litmus?

Is there some reason for omitting litmus as a pH indicator? Vaughan Pratt (talk) 07:44, 23 September 2014 (UTC)

Definition of pH is somewhat inaccurate

The definition of pH is the negative log of the activity of the proton. However, the article currently states that it is "more often expressed as the measure of the hydronium ion concentration." This is inaccurate- there is not a one-to-one mapping of hydronium ion concentration and pH. I understand the reason to include this phase- one wants the reader to develop physical intuition for pH, but this needs to be stated more clearly without the subtle implication that this is one-to-one. I would edit this page directly, but I haven't thought of an elegant way to say this without confusing the casual reader. Any thoughts, anyone?2601:A:2D80:5F:7CF1:AFAB:BF6:B5F6 (talk) 02:28, 15 May 2015 (UTC)Katie

Broken link

The chemical equilibrium#Computer programs link at the bottom of the page is missing, it links to the equilibrium page but there is nothing on computer programs. 147.69.44.14 (talk) 10:23, 19 May 2015 (UTC)

Error in applications

In the applications section the article states "Pure water does not contain any ions and therefore cannot have a pH value (log(0) is infinity)."

This isn't true. Pure water has both [H+] and [OH-] = 1 x 10^(-7) mol/L due to dissociation. So pure water has pH exactly 7.

I would edit this myself but it's my first time commenting / editing and I'm a little unsure of the conventions of behaviour. — Preceding unsigned comment added by 149.171.144.189 (talk) 00:00, 8 September 2015 (UTC)

Dimensionless concentration

For all the attention given to minutae, to difference between pH and p[H] etc, this article forgets to address the basics. pH is negative logarithm of concentration... measured in what? cm^(-3)? mM? Similarly, later in the article, dissociation constant of water is stated to be 10^(-14). It may be common practice among chemists to omit stating concentration units when referring to mol/litre, but this is essentially jargon, and as such it should not appear in an encyclopaedic article on such a fundamental concept in chemistry! A physics teacher in me would give this article a solid "F" on this account alone. — Preceding unsigned comment added by 137.205.183.109 (talk) 16:11, 1 May 2015 (UTC)

I have added the units, which (as a physics teacher) I believe are indeed "moles per litre." Mike Stone (talk). —Preceding undated comment added 15:55, 25 October 2015 (UTC)

Really exactly 7? Why such a nice round number?

It isn't at all clear why neutral should be exactly 7. Why wouldn't it be some randomish thing like 6.99989357325623562345... instead?

Perhaps it is, and everybody is just rounding?

97.104.85.21 (talk) 04:51, 11 October 2015 (UTC)

Yes- pH 7 as neutrality is an approximation. Neutrality can be defined as having [H+] = [OH-] (or perhaps activity rather than concentration, but for dilute solutions and with activity coefficients for monovalent ions being similar, it is nearly the same thing). Given that and the fact that their product [OH]*[H] = Kw, it can be seen that at neutrality [H]=[OH]=sqrt(Kw), or pH = pKw/2. pKw is a value which depends on for example temperature and ionic strength, so the exact pH of neutrality does also. Pure water and a solution of NaCl in pure water are both neutral, because dissociation of water produces equal number of H+ and OH-. However due to the effect of ionic strength on Kw, the pH of the neutral NaCl solution is slightly different from that of neutral water. I will try to clarify this. — Preceding unsigned comment added by Eaberry (talk • contribs) 01:01, 29 January 2016 (UTC)

pH does not measure alkalinity

the first sentence in the definition includes : "numeric scale used to specify the acidity or alkalinity" pH does not measure Alkalinity but Basicity. see the definition of alkalinty in wikipedia and other sources to understand why. — Preceding unsigned comment added by 80.178.190.212 (talk) 13:41, 24 November 2015 (UTC)

The pOH section implies that pOH is alkalinity which is also not true! (I have not removed this but would like to set some kind of error marker, unfortunately I don't know how to do that) — Preceding unsigned comment added by 150.227.15.253 (talk) 08:48, 10 August 2016 (UTC)

I removed the word alkalinity from the pOH section. Also, pH does not measure basicity or alkalinity. pH measures hydrogen ion activity. pOH measures hydroxide ion activity. Alkalinity is the word usually used to describe what is technically basicity, the amount of bases in a material which can accept a hydrogen ion. Acidity is the amount of acids in a material which can donate a hydrogen ion. (Definitions from Bronsted-Lowry theory of acid/base activity)Trfeick (talk) 08:40, 19 August 2016 (UTC)

pH and temperature

The dissociation product of water varies strongly with temperature. In hot water it much larger than 10^-14 which implies that neutral pH should be clearly less than 7, but maybe some type of normalization is used to keep it at 7. It would be good if some knowledgeable person could add a section on this issue. — Preceding unsigned comment added by 150.227.15.253 (talk) 08:56, 10 August 2016 (UTC)

pH is a measure of the thermodynamic activity (effective concentration) of hydrogen ions in an aqueous solution. When water dissociates, equal amounts of hydrogen and hydroxide ions are produced. They cancel each other out. The absolute concentration of hydrogen ions increases as the temperature increases, but the effective concentration, and therefore the pH, is unchanged. Trfeick (talk) 09:02, 19 August 2016 (UTC)

The p in pH

I have yet another interpretation of pH that was given to me by a very experienced chemist who has long since retired, and it is that p is as close as an English language typewriter can get to the Greek letter ρ (lower case rho), the chemical symbol for Inverse. ☺ Dick Kimball (talk) 16:23, 3 November 2016 (UTC)

Remove erroneous example

Removed the following because it is wrong. 5e-6 ions per mole of water equals 1 ion per 3.6 metric tons of water. I'm not sure what the correct formulation for this example would be, but the original is clearly off by many, many orders of magnitude.

In way of example, an aquatious solution with 5x10^-6 hydrogen ions per mole of solution has a pH of:

$5\times 10^{-6}=1\times 10^{-5.3}$

hence,

$ph(5\times 10^{-6})=+5.3$ — Preceding unsigned comment added by Ryanrs (talk • contribs) 13:18, 30 January 2016 (UTC)

To be exact, the example is off by a factor of exactly Avogadro's number. Why remove an otherwise numerically correct example when you could have fixed it simply by inserting "moles of" before "hydrogen ions"? (And correct "aquatious" to "aqueous".) Vaughan Pratt (talk) 22:53, 25 May 2016 (UTC)

This example (without "aqueous" since it holds for any solution) now appears near the beginning of the article, along with the example of pH of pure water. Vaughan Pratt (talk) 02:00, 26 May 2016 (UTC)

I agree with Pratt. Wikipedia often hides or omits the information one is seeking in a particular paragraph or even whole article (longitude latitude i had a dispute with, also meniscus, many others).

pH is the concentration (the simple ratio) of (H) + ions to neutral ions, so if the concentration is 10^-7 the pH is 7 which is called "neutral" (but is not zero). The paragraph dresses up the subject to be more difficult or even not the same as it is. The mention of logarithms has absolutely nothing to do with the matter, confuses the matter: and how to use logarithms is not described correctly or at all. the notation: varies from other text as well. — Preceding unsigned comment added by 72.219.207.25 (talk) 23:43, 20 April 2017 (UTC)

(I did exactly what i said not to unfortunately.) Most importantly: a pH of 10^-8 is less than 10^-6, a higher pH means less H+ ions and more anions (OH-, roughly speaking). It's a matter if simple counting. — Preceding unsigned comment added by 72.219.207.25 (talk) 01:23, 21 April 2017 (UTC)

Seawater

There is more written here about seawater than seems warranted, imho. I find the discussion of seawater and, for that matter, the entire article, flawed. There are multiple anions present in seawater and the most common are chloride, sulfate, bisulfate, carbonate, bicarbonate, bromide, and fluoride. The two "corrected" sea water scales mentioned do not mention carbonate/bicarbonate at all. There is no general purpose way to correct the membrane potential (or electrode potential) for specific interactions between the surface and chemicals present in the solution (these may include colloidal and even suspended solids). It is usually necessary to remove the dissolved gasses present in seawater to get consistent readings. Unfortunately, that compromises the goal of the measurement, it affects the pH of the liquid. There are plenty of PRACTICAL books on pH which basically say that the best definition of pH is what a properly calibrated and standardized pH meter measures. (With the implicit or explicit admission that this pragmatic approach will not produce the actual -log[A_h+].)98.21.243.206 (talk) 23:59, 4 May 2017 (UTC)

First Sentence

"In chemistry, pH (/piːˈeɪtʃ/) (potential of hydrogen) is a logarithmic scale used to specify the acidity or basicity of an aqueous solution"

Having "(potential of hydrogen)" on the first line is misleading towards what the p in pH stands for. There is a paragraph later on discussing what the origin of the term "pH" is, and says it is disputed. The "(potential of hydrogen)" should be removed, as it doesn't provide anything for the sentence, but contradicts later paragraphs. — Preceding unsigned comment added by 137.205.115.191 (talk) 10:26, 1 June 2018 (UTC)

Semi-protected edit request on 1 June 2018

Change "In chemistry, pH (/piːˈeɪtʃ/) (potential of hydrogen) is a logarithmic scale used to specify the acidity or basicity of an aqueous solution." to "In chemistry, pH (/piːˈeɪtʃ/) is a logarithmic scale used to specify the acidity or basicity of an aqueous solution." 137.205.115.191 (talk) 11:14, 1 June 2018 (UTC)

Done. Vsmith (talk) 12:29, 1 June 2018 (UTC)

Semi-protected edit request on 16 June 2018

ytrytryhrtytrtrytryrtytrytryrtytryrtyry 74.134.221.136 (talk) 21:44, 16 June 2018 (UTC)

 Not done I don't think this would be a good addition to the article. StraussInTheHouse (talk) 21:46, 16 June 2018 (UTC)

pH 7 or 7.000 is not neutral!

Neutrality can be defined as [H⁺] = [OH^-] pr pH = pOH = 1/2 pKw.

But pKw is a physical constant that depends on things like temperature, ionic strength, pressure. Under physiological conditions it is approximately 14, so the neutral point is when pH = pOH = ~7.0. The variation is slight enough in aqueous solutions that we can say pH 5 is acidic and pH 9 is basic, but we cannot say pH 6.8 is slightly acidic unless we know the value of pK_w under the extant conditions! It might be well to replace 7 with "~7.0 at room temperature" Eaberry (talk) 05:04, 25 October 2018 (UTC)

Negative pH

I see that this semi-protected article has a sentence in the lede: Contrary to popular belief, the pH value can be less than 0 or greater than 14 for very strong acids and bases respectively (with a reference to an Journal of Chemical Education article). This sentence is not further detailed in the content sections and thus the issue of negative pH significance is left in suspension. Some explaining sentences would be useful. (This is also intended as semi-protected edit request).--5.2.200.163 (talk) 11:36, 4 July 2018 (UTC)

I'll just leave this here, if someone wants to add detail from it. The referenced entry in the journal includes: "For example, commercially available concentrated HCl solution (37% by mass) has pH ≈ –1.1, while saturated NaOH solution has pH ≈15.0 (22). Hot springs near Ebeko volcano, with naturally occurring HCl and H2SO4, have estimated pH values as low as –1.7 (23, 24). Waters from the Richmond Mine at Iron Mountain, CA, have pH = -3.6 (25, 26)"; the citations being:

• (22) Dickerson, R. E.; Gray, H. B.; Darensbourg, M. Y. Chemical Principles, 4th ed.; Benjamin Cummings: Menlo Park, CA, 1984
• (23) Ivanov, V. V. Geokhimiya 1955, 1, 63.
• (24) Nikitina, L. P. Presented at Proceedings of the Water-Rock In-teraction Symposium, Prague, Czechoslovakia, 1974.
• (25) Nordstrom, D. K.; Alpers, C. N. Proc. Natl. Acad. Sci. U.S.A. 1999, 96, 3455.
• (26) Nordstrom, D. K.; Alpers, C. N.; Ptacek, C. J.; Blowes, D.W. Environ. Sci. Technol. 2000, 34, 254.

--Inops (talk) 14:26, 10 August 2018 (UTC)

I was surprised to see the reference to "popular belief". I have never heard of any such restriction to between 0 and 14. That would be saying the H⁺ concentration cannot go over 1M or under 10^-14 M. Eaberry (talk) 05:21, 25 October 2018 (UTC)

Semi-protected edit request on 17 October 2019

Please provide a quantitative estimate for the difference between the total and seawater pH scales (in seawater). To do that, change "very small" to "very small (about 0.01)". I am a marine chemist specialized in the carbon cycle. OAguy (talk) 16:56, 17 October 2019 (UTC)

 Not done: please provide reliable sources that support the change you want to be made. Unfortunately, personal knowledge isn't sufficient. The information needs to be verifiable in a reliable, published source. See also Wikipedia's policy on original research. ‑‑ElHef (Meep?) 18:02, 17 October 2019 (UTC)

pH indicators

I think the main article that is linked to by the pH indicators section needs to be pH indicator not Universal indicator since there are many pH indicators and universal indicator is just one. Jasoninkid (talk) 22:41, 12 June 2020 (UTC)

Seems reasonable. Done.  Velella  ^{Velella Talk}   22:50, 12 June 2020 (UTC)

Do you think there should be something about OH- (hydroxide) ions in the main blurb?

I'm not an expert in chemistry specifically but it is very tangential to my field... this youtube video gives a very clear and concise explanation, assuming its not oversimplified or wrong...? https://www.youtube.com/watch?v=E7qXfON0yG8

Should this content in written form be perhaps included in the main blurb? — Preceding unsigned comment added by 50.102.78.63 (talk) 13:41, 27 May 2020 (UTC)

I do think this need to be in there. In fact the opening paragraph that describes pH as the concentration of hydrogen ions is just plain wrong. The pH scale is based on the ratio of protons(H+ not H-) to hydroxide ions. The same ratio can be achieved at very high or very low concentration and the pH will remain the same. — Preceding unsigned comment added by 73.193.32.170 (talk) 04:47, 11 July 2020 (UTC)

Add to pH indicator table colors?

In regard to the pH Indicator table (under the Definition and measurement section), I was thinking we might better assist colorblind readers by adding a column explicitly stating the color used in each row. I would do it myself, but I'm not really familiar with tables --Pythagimedes (talk) 05:35, 24 January 2021 (UTC)

punctuation: the comma with 'or'

if alkaline means "basic" then there should be a comma before 'or' ("basic, or alkaline"). When there is no comma before "or" it would means that 'basic' and 'alkaline' are two separate things. so which is it? Because "..., or" means "in other words". Hope you can clarify. Stjohn1970 (talk) 14:18, 15 May 2021 (UTC)

GoodGod21 (talk) 03:50, 9 November 2021 (UTC)

pH

What are the biomedical importance of pH 197.231.239.23 (talk) 07:14, 6 February 2022 (UTC)

Typo or miscalculation in example?

The example in section Definition and Measurement reads:

Consider the following example: a quantity of 107 moles of pure water at 25 °C (pH = 7), or 180 metric tonnes (18×107 g), contains close to 18 g of dissociated hydrogen ions. Should it be changed to "...close to 18 milligrams of dissociated hydrogen..."? DrDoglovich (talk) 17:19, 9 August 2022 (UTC)

1000 L/m^3. 1e7 moles *18g/mole is 180t, or 180,000L. 1e-7 mole/L, .018 moles, 18g/mole, 0.324g. How much does a cubic meter of oriental soup weigh? Gah4 (talk) 23:09, 9 August 2022 (UTC)

Not 18g/mol, dissociated hydrogen ions weight 1 g/mol. 0.018 moles of them weigh 0.018 grams, or 18 milligrams. Right? DrDoglovich (talk) 18:30, 11 August 2022 (UTC)

Oh, ok. Well, they should be hydronium ions, but otherwise that sounds fine. Gah4 (talk) 01:21, 12 August 2022 (UTC)

Symbol definition?

Should we not define the symbol $[H^{+}]$ when it is first used? Orginally we had Ph defined as approximately $-\ln _{10}a,$ where $a,$ is the activity which, for dilute solutions, is roughtly the concentration of the $H^{+}$ ions in Moles per litre. When I first went to the article it said that concentrations were dimensionless but I was there to find out if was to find out if Chemists used moles per litre or moles per cubic meter in the definition of Ph. I imagine that many non-chemist people turning to the article have questions like this. Mike Stone (talk) 23:05, 10 March 2023 (UTC)

Hello! According to IUPAC there is no [H⁺] in the pH definition (neither in notional, nor instrumental definition). Just activity. But for most people activity is extremely complicated matter for understanding. So, my suggestion use ≈ symbol after the definition with activity to the estimation with [H⁺]. It may be the reason to think what is the difference between the activity an concentration. On the other hand, others just use formula with concentration and it will be fine with them. ChemEdit (talk) 07:15, 20 March 2023 (UTC)

Wiki Education assignment: CHEM 300

This article was the subject of a Wiki Education Foundation-supported course assignment, between 9 January 2023 and 28 April 2023. Further details are available on the course page. Student editor(s): Veggietaquito (article contribs). Peer reviewers: Mimosa taco.

— Assignment last updated by RS UBC800 (talk) 21:05, 2 April 2023 (UTC)