Talk:PH/Archive 3

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)^[1], 7.6 in 60 degree F waters and 7.3 in 80 degree F waters^[2], between 7.2 and 7.6^[3], and 7.2, with an acceptable range of between 7.0 and 7.6^[4]. 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)

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)

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

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

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)

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)

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)

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)

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)

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)

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)

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:

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

hence,

${\displaystyle ph(5\times 10^{-6})=+5.3}$ — 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)

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)

"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)

This edit request to PH has been answered. Set the |answered= parameter to no to reactivate your request.

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)

This edit request to PH has been answered. Set the |answered= parameter to no to reactivate your request.

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)

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)

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)

This edit request to PH has been answered. Set the |answered= parameter to no to reactivate your request.

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)

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)

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)

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)

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)

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

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)

Should we not define the symbol ${\displaystyle [H^{+}]}$ when it is first used? Orginally we had Ph defined as approximately ${\displaystyle -\ln _{10}a,}$ where ${\displaystyle a,}$ is the activity which, for dilute solutions, is roughtly the concentration of the ${\displaystyle H^{+}}$ 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)

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)

I've stumbled over this sentence in this article: The pH of seawater is typically limited to a range between 7.4 and 8.5. as the value of 7.4 seemed way too low to me. This sentence actually talks about extremes of pH value rather than describing what the "normal" range is. The same sentence is currently also at seawater and at ocean and I plan to change it in all three places (am pondering if the same info really should be in 3 articles though; see below). I've contacted an ocean chemistry expert about this sentence (Tim Jickells) and he recommended changed it like this: The pH value at the surface of oceans is normally about 8.2 and can fall to 7.8 in deep ocean waters as a result of degradation of organic matter in these waters (Emerson and Hedges chapter 4) and can be as high as 8.4 in surface waters in areas of high biological productivity (Chester and Jickells Chapter 9).. Does anyone object? He also said "I think chasing extreme pH values is probably misleading". Pinging User:Plumbago who has worked on this before. Also pinging User:Epipelagic and User:ASRASR.

I think this whole pH thing in the ocean is so important now because ocean acidification results in a dropping pH value so it's important to get all the facts straight and clear.

My second question is: would the info about the pH value in the ocean perhaps be better off centralised in one article and then the other articles should refer across, rather than repeating the same info in several places? At the moment, the same/similar about current pH value info would be in these articles: pH, sea, ocean, seawater, ocean acidification. Can we envision any streamlining for this? Maybe by using excerpts? As the pH value will continue to drop over time (even if slowly), this will be an ongoing issue. EMsmile (talk) 12:41, 2 May 2023 (UTC)

I've now removed that sentence in question and modified the section a bit. I've updated the content about a drop in pH value by copying some sentences from ocean acidification which were recently updated there. I'll now also update the equivalent content at sea, ocean, seawater. EMsmile (talk) 07:32, 3 May 2023 (UTC)

Thanks for this. I think Jickells' revised sentence is good. According to NOAA (https://www.noaa.gov/education/resource-collections/ocean-coasts/ocean-acidification#:~:text=Because%20of%20human%2Ddriven%20increased,the%20ocean%20becomes%20more%20acidic) the average pH of the oceans has dropped to 8.1 over the past 100 years. Setting up excerpts to the relevant WP articles is a good idea in order to create consistency. ASRASR (talk) 22:56, 22 May 2023 (UTC)

I'm no subject expert but after reading the cited source "Negative pH Does Exist" and the lead's mention that pH can fall outside [0, 14], I felt confident enough to make this edit that removes reference to 0 and 14 as bounds. The first text removed contains information found elsewhere in the article (relationship to hydrogen ions; logs mean tenfold difference is a pH difference of 1). Then some rewording on 7 as neutral.

The article could still do a better job of explaining whether a pH of 7 exactly is or isn't true neutral (or whether it depends on some other factor like temperature), and maybe cover this [0, 14] misconception in the body of the article with some examples outside this interval. — Bilorv (talk) 08:47, 9 August 2023 (UTC)

I've added this back to the lead "The pH range is commonly given as zero to 14" - I think it's useful to have this as these are the "normal" limits (isn't it?) and anything that is below zero or above 14 is very rare, right? And I think we should probably explain this a bit better in the main text. EMsmile (talk) 14:28, 14 August 2023 (UTC)

But it's false. NaOH and HNO₃ are pretty common reagents, including at the concentrations required to get out of the [0, 14] range.

What is true is that as you get beyond the usual range, pH stops being a good measure. For example, at such high concentrations, activity and concentration can no longer be assumed equal. Double sharp (talk) 08:00, 9 December 2023 (UTC)

Hi! I am a retired research chemist and teacher of chemistry at varios levels. You seem to think negative pH is uncommon, rare. It isn't. You also need to understand the ifference between "strong" and "concentrated" and to keep these terms separate. In a teaching lab, there are often racks of common reagent dilute solutions, and to simplify proportion-judging, they are of similat concentrations, typically 2 mol/litre. Thus "dilute Hydrochloric acid" will be 2M, but sulfuric acid will be 1M (as it dissociates one H2SO4 giving two H+). Not really "concentrated", and activity still close to molarity. Now minus log10 of 2 is minus 0.3, so there's a negative pH. (most pH test strips would show "zero", really meaning "below 0.5") Many household chemicals in solution would reach that too, eg, "pH Reducer" for pools/spas.Agreed, at higher concentrations, activity not equal molarity. But 10M acids are easy (pH approx -1), but 100M acids are not (even neat water is only 1000/18 = 55.6M). 100M would be -2, so the scale must give out somewhere between -1 and -2, and similarly at the other end of the scale. Things get really weird in non-aqueous solutions, so don't go there! Regards, Bob. Bobgid (talk) 15:24, 30 March 2024 (UTC)