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I added "parts hydrogen" to clearly define that pH is a direct measurement of the concentration (parts) of hydrogen ions in a liquid (compared to distilled water). --Lperez2029 13:09, 15 December 2006 (UTC)
pH is the symbol for the logarithm of the reciprocal of hydrogen 'ion concentration' in gram atoms (parts) per liter. For example, a pH of 5 indicates a concentration of .00001 or (10 to the power of 5) gram atoms of hydrogen atoms in one liter of solution. Therefore, pH measurement may be expressed as parts (ion potential) hydrogen, or pH (potential hydrogen), either way it is acceptable in definition terms, but "parts" hydrogen is more correct (as would the expression of ppm (parts per million). No edit wars - I'll bring some top chemists into the discussion, and we will see what is more correct for pH definition for the benefit of all, once and for all. Best regards --Lperez2029 00:39, 17 December 2006 (UTC)
pH literally means negative the log of the hydrogen ion 'activity' in solution; it is commonly written -log[H+] meaning -log of the hydrogen ion concentration. In the common solvent water, a bare hydrogen ion is solvated by the water forming the hydronium ion [H(H2O)]+, so pH is also commonly written -log[H3O+]. For example, pH=7.0 means that the positively charged hydrogen ion concentration in solution is 1x10-7 moles H+/liter, since -log(1x10-7) = 7. Normally, pH would therefore be close in meaning to parts hydrogen (as in ppm) with the understanding that hydrogen means positively charged hydrogen ions in solution; whether the concentration is reported as pH, ppm, g H+/liter, wt%, etc., - moles H+/liter, ie concentration, is the basic chemical term.
There are some fine points here. The 'activity' or 'effective concentration' of H+ is what's measured by a pH meter electrochemically. In dilute solution, the 'activity' and actual concentration of H+ are indistinguishable; activity = concentration. As concentration increases, relative 'activity' decreases due to a chemical thermodynamics concept called chemical potential. Activity < concentration, and concentration H+ is undermeasured by the pH meter because the 'activity' is lessened due to this thermodynamic ionic shielding factor. (The actual H+ concentration could be measured by other means such as titration). So, in this context, one might say that the 'p' has to do with the potential H+ concentration (which is activity) which is less than the actual H+ concentration.
Water does inherently dissociate. Pure water, under 'standard' conditions, dissociates from H2O into hydrated H+ and OH- to the extent of 1x10-7 moles/liter, also called pH 7 or neutral pH, the pH where there is no excess of acid (H+) or base (OH-). Regardless of the early 1900's origins of the use of p in pH, consistent with the meaning of 'p' in descriptions of other chemical equilibria, such as pK, the p of pH nowadays is taken to mean -log.
Now, let the statement speak for itself - as for adding 'parts', I'll leave that up to you gentlemen. Best regards --Lperez2029 22:17, 18 December 2006 (UTC)
Thanks Edward. --Lperez2029 23:17, 21 December 2006 (UTC)
It is suggested that pH stands for "pondus Hydrogenii" (=~ weighting of hydrogen-ions). --march 15, 2009 —Preceding unsigned comment added by 85.81.91.41 ( talk) 14:28, 15 March 2009 (UTC)
"pH is a measure of the acidity of a solution in term of activity of hydrogen (H+). "
Wait but pH also measures the alkilinity of a substance. Is there a seperate test for this? Simply south 15:34, 21 December 2006 (UTC)
To more specifically answer your question; no, there is no separate test necessary to measure alkalinity in a solution, the test may be performed utilising a pH meter or litmus paper. The introduction on the article should read more along the lines pH is a measure of the acidity or alkalinity of a solution in terms of activity of hydrogen (parts Hydrogen). For example; 4= Acidity - - 7pH=pure water - - 12=Alkalinity (or base) --Lperez2029 13:20, 22 December 2006 (UTC)
Alkalinity is not the opposite of acidity. Alkalinity is a measure of the buffering capacity against the addition of H+. And yes, there is a separate test for this (titration). pH is a measure of the H+ activity. period. From this 'basicity' can be determined, if you know the pKw (ie pOH = pKw - pH)(the pKw shouldn't be assumed to be 14 - it is rare to have standard conditions), but there is no way to determine alkalinity from pH as you need to take into account a wide variety of other ions that contribute to alkalinity (ie At = OH- + HCO3- + CO3-- + B(OH)3 + ...). It is likely that there is a way to measure basicity ( ie [OH-]), though it is presumably much easier to measure acidity ([H+]). Piyrwq 16:43, 12 January 2007 (UTC)
Anybody else have a problem with this statement: "strictly speaking, there is no such thing as the H+ ion"? There certainly is such a thing as the H+ ion. It is called a proton and exists discretely in the in the state of matter known as plasma if nowhere else. If nobody objects, I would like to change this statement to read: "in aqueous solution the H+ ion does not exist independently but is actually the third hydrogen atom in H3O+, called the hydronium ion." Thoughts? Objections? Schlemazl 21:53, 13 February 2007 (UTC)
Also, I'm being driven a little crazy by the addition of "basicity" or "alkalinity" to the definition of pH. Knowing [H3O+] does not mean you know [OH-] (basicity). If you have the literature resources at hand, measured temperature, and know the specific nature of other ions in solution you may be able to calculate basicity from the pH, but one does not define the other. It definitely does not give any insight into alkalinity. For example, it is possible to reduce pH of a solution, through the addition of CO2, while alkalinity remains constant Alkalinity#Addition_of_CO2- alkalinity is absolutely not defined by the log of hydrogen concentration, nor is basicity. These are concepts worthy of much discussion, but are not fitting for the definition of pH. Can we come to some kinda consensus, so that references to basicity and alkalinity can be permanently removed from the definition of pH? Piyrwq 02:41, 14 February 2007 (UTC)
Ok, I have rewritten the whole first paragraph - I hope it is an improvement, but no doubt there is still a lot to be changed. For reference, here is the old version, which I felt was over complicated and too wordy.
pH is a measure of the
acidity and the
basicity/alkalinity of a
solution in terms of
activity of
hydrogen (
H+). In
aqueous solutions H+ ions bind to water molecules forming
hydronium ions, or H3O+. For dilute solutions, however, it is convenient to substitute the activity of the hydrogen ions with the concentration,
molarity (mol/L) of the hydrogen ions (however, this is not necessarily accurate at higher concentrations
[1]
[2]).
In aqueous systems, the hydrogen ion activity is dictated by the dissociation constant of water ( Kw = 1.011 × 10−14 M2 at 25 °C) and interactions with other ions in solution. Due to this dissociation constant, a neutral solution (hydrogen ion activity equals hydroxide ion activity) has a pH of approximately 7. Aqueous solutions with pH values lower than 7 are considered acidic, while pH values higher than 7 are considered basic.
The concept was introduced by S.P.L. Sørensen in 1909, and is purported to mean pondus hydrogenii in Latin. [3] However, most other sources attribute the name to the French term pouvoir hydrogène [4] [5] [6]. In English, pH can stand for "hydrogen power," [4] [5] [6] "power of hydrogen," [7] [8] or "potential of hydrogen." [3] [9] [10] All of these terms are technically correct.
Conrad.Irwin 10:10, 21 February 2007 (UTC)
This is incorrect. In 2000, Jens Nørby, a Danish biochemist, went back to Sørensen's original papers on the subject: "But Nørby traces the 'p' to a simple mathematical convention of naming variables. (...) But he did not give an explicit reason for choosing 'p' in his original two papers. Sørensen was primarily concerned with determining the H+ concentration electrometrically. His central equation involved values for measurements at two electrodes, which he arbitrarily designated p and q. To develop a standard, he set the non-hydrogen component, Cq, at 1.0 and solved for the hydrogen ion concentration, Cp, or 10–p. The number p he suggested calling p+H."
Source: http://www1.umn.edu/ships/words/pH.htm which is a summary of the original article: Nørby, Jens. 2000. The origin and the meaning of the little p in pH. Trends in the Biochemical Sciences 25:36-37. ($31.50) —Preceding unsigned comment added by 75.74.75.149 ( talk) 20:05, 1 February 2009 (UTC)
Regarding "By virtue of its logarithmic nature, pH is a dimensionless quantity." IANACB (I am not a chemist, but..) is it truly because of its logarithmic nature? Wouldn't say, a quantity expressed as "log10 lightyears" still be very much a dimensioned distance? Does the dimensionless of pH perhaps have nothing to do with logarithims and everything to do with the value whose logarithm is being taken? If I'm wrong here, thanks for your patience in considering this. —Preceding unsigned comment added by Dfgriggs ( talk • contribs) 18:22, 22 November 2008 (UTC)
The present intro says, "It is unknown what the exact definition of p stands for. Some references suggest the p stands for “Power”[2], others refer to the German word “Potenz” (meaning power in German)[3], still others refer to “potential”."
To be fair, "power", "potenz", & "potential" are all rough synonyms. Ventifax ( talk) 00:00, 1 April 2009 (UTC)
____________________________________________________________
pH is the abbreviation of the latin expression pondus Hydrogenii (pondus = pressure, hydrogenium = hydrogen) —Preceding unsigned comment added by 165.228.210.24 ( talk) 04:59, 2 April 2009 (UTC)
The article states: Most substances have a pH in the range 0 to 14, although extremely acidic or extremely basic substances may have pH less than 0 or greater than 14. An example is acid mine runoff, with a pH = -3.6. Note that this does not translate to a molar concentration of 3981 M.
But it also states that pH is, strictly speaking, a function of the activity of hydrogen ions in solution, not their concentration. And that is acknowledged by references. Now, a careful look at Wikipedia's article on Activity, or preferably to a Physical Chemistry book, will lead you to see that Activity ranges from ZERO to ONE, and is never higher than one, because pure substances have an activity of 1 by definition (it was meant to be analogued to molar fraction, and molar fraction can never be greater than 1 either).
Now pick a calculator and verify the value of -log(1), the result is 0, and that is the lowest pH a substance can ever have. Strictly speaking, pH can never be lower than zero, except when calculated in a less rigurous way, using molarity or molality: but that is incorrect, and should be pointed out. pH lower than zero may be obtained by other ways, maybe (pH-meter?), but it should be clearly specified how was that value obtained, what does it mean (because if it has no meaning, is serves no purpose and shouldn't be used), and emphasis should be put on that strictly speaking, the pH of a solution can never be lower than 0 (because activity ranges from 0 to 1, and therefore -log(act) ranges from 0 to positive infinity). I'll wait for answers regarding this before modifying the article myself. 158.170.51.28 14:50, 27 December 2006 (UTC)
Was added by User:69.140.68.72 and removed by me. A Google search brings up 20 hits. The top four English resources (disregarding Wikipedia's status as first):
— Edward Z. Yang( Talk) 15:03, 19 February 2007 (UTC)
This article needs a nice image to plaster on the top of the document. One can't really photograph pH, though, so we've got to pick something fairly representative. Candidates:
Possible candidates? (add ones you find to the gallery below) — Edward Z. Yang( Talk) 21:53, 21 February 2007 (UTC)
Not experienced with this, but i cant seem to delete the vandelism :( —The preceding unsigned comment was added by 129.234.4.76 ( talk) 14:50, 24 February 2007 (UTC).
Also there seems to be a discrepancy between tables "Representative pH values[citation needed]" and "pH in body fluids [13]" Apologies if this is in the wrong place but text editing is not my forte. -->Check the Gastric Acid #'s
I propose we semi-permanently semi-protect this article. The amount of vandalism it receives is absolutely ridiculous. — Edward Z. Yang( Talk) 22:36, 1 March 2007 (UTC)
I think it would be interesting to have some biological Ph values for comparison. For example the stomach. Also according to de.wikipedia wine has Ph 4, there is a hole there in the english table. -- 172.174.140.43 07:47, 4 March 2007 (UTC)
I actually wanted to look at the page "pH-imbalance", meaning in the body, but I just got redirected to pH.
If somebody feels up to the job, you might want to incorporate the fact that there are three different scales for pH in place, as a recent discussion on the talk page to the article ocean acidification has showed. Hardern 12:01, 13 April 2007 (UTC)
Two problems with the following:
Firstly, the word lemonade refers to totally different drinks in the UK and USA. The carbonated drink commonly known as lemonade in the UK (and limonade in France) is better known as Sprite in the US, but without the lime flavo(u)r. Secondly, the article does not state whether 0.0050M is a reasonable proton concentration for lemonade - is this a hypothetically concentrated lemonade that nobody would want to drink, or a realistic one? The article on lemons says that pure lemon juice has a pH of 2 to 3, and the article on acetic acid says vinegar has a pH around 2.4. Assuming that lemon juice in lemonade is diluted with about 5 parts water, this would give it a pH 0.8 higher than pure juice - and I would also assume that (American) lemonade is less acidic than vinegar, if sourness is any guide to pH. Mtford 06:36, 10 May 2007 (UTC)
If it's real, it seems that Phidron would be better as part of this article. A search of Google Scholar did not find any references to phidron. Most of those in Google itself are apparently based on this article. ChemGardener 19:55, 28 May 2007 (UTC)
"However pH is actually a shorthand for its mathematical approximation: in chemistry a small p is used in place of writing − log10 and the H here represents [H+], the concentration of hydrogen ions."
My understanding was that the use of p as shorthand to mean -log developed from pH, not the other way around, so I'm pulling this unless someone can source it.
Orange32 03:35, 27 August 2007 (UTC)
I am adding one more question to this. Is it usually written as pH, I mean is 'H' a superscript of p or is it just pH? Elncid ( talk) 12:33, 20 December 2007 (UTC)
This may require a separate article, and I am not an expert (or even proficient) by any means on the following, but the following sections seem to be missing:
Perhaps a separate article may be needed. — Rob ( talk) 20:05, 15 October 2007 (UTC)
Hear, hear. —Preceding unsigned comment added by 58.109.98.211 ( talk) 06:28, 27 November 2007 (UTC)
I don't understand something from this artical, Im a fifth grader so this question must seem stupid to most of you but the less acidic something is like pure water you would say want to put a fish in it, at least someone told me at a feild trip. So you want to put fish in bleach and household lye? —Preceding unsigned comment added by 76.104.227.88 ( talk) 04:23, 29 November 2007 (UTC)
This article is too confusing for someone who just wants a simple explanation of pH. It needs a better introduction and some explanation in words, not just math. —Preceding unsigned comment added by Amberlianne ( talk • contribs) 03:22, 9 March 2008 (UTC)
I wholly agree with this. pH is just a simple acidic calculator, not 10 mathematic equations which have nothing to do with acids and science. Same with Circumference. Koshoes ( talk) 18:54, 25 January 2009 (UTC)
Indeed! I have a PhD in Computer Science and informal Chemical education, and I find this article level totally inappropriate. I think the "solution" is to split it into an "Exact definition of pH for Chemical Engineering" and keep "pH" as a high-school grade article which does not make references to "activity" at all. A basic article on pH should follow most biology/chemical 101 text, defining it as -log [H+] using molarity, and giving specific examples of actual pH and its importance to the human body and simple solutions (eg swimming pools, fish tanks, etc)
see for exmaple http://antoine.frostburg.edu/chem/senese/101/acidbase/faq/what-is-pH.shtml
Is there a simple way for the article writers and editors to state plainly the question, "What is pH?" 70.231.150.141 ( talk) 02:11, 19 March 2008 (UTC) In a simple way for any range of high school student down to elementary school student to understand? Thanks. 70.231.150.141 ( talk) 02:13, 19 March 2008 (UTC) Wait, I'll post it as best as I can. —Preceding unsigned comment added by 70.231.150.141 ( talk) 02:14, 19 March 2008 (UTC)
I think the article would be clearer if we dropped most references to hydronium ions (H3O+) in favour of hydrogen ions (protons, H+).
When you consider the solvation, H3O+ isn't all that accurate anyway - it's more like H9O4+ but this depends on temperature. So H3O+ isn't much more accurate as a description of what protons do in aqueous solution than writing H+ (aq). However, writing H+ is much simpler and scarcely less accurate.
Ewen ( talk) 08:33, 23 March 2008 (UTC)
Reworking the introduction section somewhat, how does this sound?
I've tried to limit the hydronium ion stuff (not least because the hydrogen ion pages points to other hydrates of protons, and implies that "hydrogen ion" is favour by IUPAC), and have broken the text up into several more readable (to me) paragraphs. I've also extended the mention of acids and alkalis, since this seems pretty important to me.
Anyway, I'm no chemist, so may have botched some of the above. Comments welcome. If I don't hear anything at all, I'll replace the current intro with the above. Cheers, -- Plumbago ( talk) 16:05, 4 April 2008 (UTC)
The assertion that pure water is pH 7 will confuse budding experimentalists who find that their "pure" water is acidic. Perhaps it would be appropriate to mention that pure water exposed to the atmosphere becomes acidic as CO2 combines with water to form carbonic acid. This is often a point of confusion as folks are experimenting with pH. JonMoulton ( talk) 20:36, 8 April 2008 (UTC)
In text: "But here we define a strong acid as a species which is a much stronger acid than the hydronium (H3O+) ion. In that case the dissociation reaction (strictly HX+H2O↔H3O++X− but simplified as HX↔H++X−) goes to completion, i.e. no unreacted acid remains in solution"
Dissociation ?
Contributions from Brazil
user:pt:lemarlou —Preceding unsigned comment added by 189.68.63.196 ( talk) 15:05, 11 April 2008 (UTC)
There are two tables in this article. One places gastric acid at 1.5-2.0, the second places gastric acid at 0.7. Which is correct? -- Arperry ( talk) 22:28, 29 July 2008 (UTC)
I find it a little sad that both the article and the talk page currently fail to include the string "volt". So, well, at least the latter I can remedy:
At 293.15 K, a pH difference of 1 corresponds to a voltage of .05817 V, or ln(10)× R×293.15 K/ F precisely. For other temperatures, modify accordingly.
That much I am able to gather from the definition given on the page. pH meter appears to have slightly more, but could the relationship between pH and voltage on the one hand, and pH and temperature on the other hand, be made clearer to the non-experts among us?
Is it really as simple as saying that a voltmeter will display pH differences, if temperatures are constant, in the ideal case of an infinitesimal test charge being used?
RandomP ( talk) 13:51, 18 August 2008 (UTC)
http://en.wikipedia.org/wiki/Talk:PH A recent news article claimed that a pH change of as little as 0.02 units could significantly change the degree of absorption of sound in seawater, especially at low frequencies. [3] Do small pH changes also affect the speed of sound in water? To illustrate, picture a large explosive sitting on the ocean floor, and far above it a net of electrodes establishing a steady pH gradient, or a net of tubes emitting fluid of high/low pH, or a large wrapped isoelectric focusing gel... when the target sub passes overhead, the sound of the blast is refracted by differences in transmission speed, and a significant fraction of the original blast is reconstituted at the distant focal point. Or not? ;) Wnt ( talk) 17:55, 3 October 2008 (UTC)
The pH scale images are too small to interpret from the page. This would render them totally useless in printed versions. Can we get them scaled up, please? -- IronMaidenRocks ( talk) 19:02, 7 November 2008 (UTC)
Doesn't pH only go down to 0? Why does the chart say -1? Shouldn't it be edited and or deleted? I have been taught and can find no source contradicting the fact that pH goes down to 0. —Preceding
unsigned comment added by
68.33.178.97 (
talk)
04:55, 20 January 2009 (UTC)
Possibly better pH chart here:
pH chart I created it and am very open to suggestions for change. --
Hansepoo (
talk)
02:57, 8 July 2009 (UTC)
In Chemistry class today, when we were talking about the pH scale, I thought of a problem: If the concentration of H+ or OH- is less than 10-7M, taking the logarithm will result in it being over 7, which does not make sense, since how could an acid be diluted so much that is becomes a strong base, or vice-versa? I didn't see anything about it here, nor in the Chemistry book I looked at to find an answer, anyone have an explanation? -- Gimmethegepgun ( talk) 16:47, 11 March 2009 (UTC)
pH is defined as minus the decimal logarithm of the hydrogen ion activity in an aqueous solution. [15] By virtue of its logarithmic nature, pH is a dimensionless quantity.
where aH is the (dimensionless) activity of hydrogen ions. The reason for this definition is that aH is a property of a single ion which can only be measured experimentally by means of an ion-selective electrode which responds, according to the Nernst equation, to hydrogen ion activity. pH is commonly measured by means of a combined glass electrode, which measures the potential difference, or electromotive force, E, between an electrode sensitive to the hydrogen ion activity and a reference electrode, such as a calomel electrode or a silver chloride electrode. The combined glass electrode ideally follows the Nernst equation:
where E is a measured potential , E0 is the standard electrode potential, that is, the electode electrode potential for the standard state in which the activity is one. R is the
gas constant, T is the temperature in Kelvin, F is the
Faraday constant and n is the number of electrons transferred, one in this instance. The electrode potential, E, is proportional to the logarithm of the hydrogen ion activity.
-- Mrfabioc ( talk) 19:06, 3 May 2009 (UTC)
The article states that carbon dioxide is an acid, but is it right to say this? My understanding is that carbon dioxide will dissolve in water to give an acidic solution of carbonic acid, but then carbonic acid is the acid, not carbon dioxide. Baclough ( talk) 10:34, 24 May 2009 (UTC)
The article says that, "The pH for pure water at 25 °C (77 °F) is close to 7.0.". I don't think that that is true. Pure water should always have a pH of 7, no matter the temperature. Please tell me if I am wrong. Nathan.tang ( talk) 11:11, 13 July 2009 (UTC)
![]() | This page is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
I added "parts hydrogen" to clearly define that pH is a direct measurement of the concentration (parts) of hydrogen ions in a liquid (compared to distilled water). --Lperez2029 13:09, 15 December 2006 (UTC)
pH is the symbol for the logarithm of the reciprocal of hydrogen 'ion concentration' in gram atoms (parts) per liter. For example, a pH of 5 indicates a concentration of .00001 or (10 to the power of 5) gram atoms of hydrogen atoms in one liter of solution. Therefore, pH measurement may be expressed as parts (ion potential) hydrogen, or pH (potential hydrogen), either way it is acceptable in definition terms, but "parts" hydrogen is more correct (as would the expression of ppm (parts per million). No edit wars - I'll bring some top chemists into the discussion, and we will see what is more correct for pH definition for the benefit of all, once and for all. Best regards --Lperez2029 00:39, 17 December 2006 (UTC)
pH literally means negative the log of the hydrogen ion 'activity' in solution; it is commonly written -log[H+] meaning -log of the hydrogen ion concentration. In the common solvent water, a bare hydrogen ion is solvated by the water forming the hydronium ion [H(H2O)]+, so pH is also commonly written -log[H3O+]. For example, pH=7.0 means that the positively charged hydrogen ion concentration in solution is 1x10-7 moles H+/liter, since -log(1x10-7) = 7. Normally, pH would therefore be close in meaning to parts hydrogen (as in ppm) with the understanding that hydrogen means positively charged hydrogen ions in solution; whether the concentration is reported as pH, ppm, g H+/liter, wt%, etc., - moles H+/liter, ie concentration, is the basic chemical term.
There are some fine points here. The 'activity' or 'effective concentration' of H+ is what's measured by a pH meter electrochemically. In dilute solution, the 'activity' and actual concentration of H+ are indistinguishable; activity = concentration. As concentration increases, relative 'activity' decreases due to a chemical thermodynamics concept called chemical potential. Activity < concentration, and concentration H+ is undermeasured by the pH meter because the 'activity' is lessened due to this thermodynamic ionic shielding factor. (The actual H+ concentration could be measured by other means such as titration). So, in this context, one might say that the 'p' has to do with the potential H+ concentration (which is activity) which is less than the actual H+ concentration.
Water does inherently dissociate. Pure water, under 'standard' conditions, dissociates from H2O into hydrated H+ and OH- to the extent of 1x10-7 moles/liter, also called pH 7 or neutral pH, the pH where there is no excess of acid (H+) or base (OH-). Regardless of the early 1900's origins of the use of p in pH, consistent with the meaning of 'p' in descriptions of other chemical equilibria, such as pK, the p of pH nowadays is taken to mean -log.
Now, let the statement speak for itself - as for adding 'parts', I'll leave that up to you gentlemen. Best regards --Lperez2029 22:17, 18 December 2006 (UTC)
Thanks Edward. --Lperez2029 23:17, 21 December 2006 (UTC)
It is suggested that pH stands for "pondus Hydrogenii" (=~ weighting of hydrogen-ions). --march 15, 2009 —Preceding unsigned comment added by 85.81.91.41 ( talk) 14:28, 15 March 2009 (UTC)
"pH is a measure of the acidity of a solution in term of activity of hydrogen (H+). "
Wait but pH also measures the alkilinity of a substance. Is there a seperate test for this? Simply south 15:34, 21 December 2006 (UTC)
To more specifically answer your question; no, there is no separate test necessary to measure alkalinity in a solution, the test may be performed utilising a pH meter or litmus paper. The introduction on the article should read more along the lines pH is a measure of the acidity or alkalinity of a solution in terms of activity of hydrogen (parts Hydrogen). For example; 4= Acidity - - 7pH=pure water - - 12=Alkalinity (or base) --Lperez2029 13:20, 22 December 2006 (UTC)
Alkalinity is not the opposite of acidity. Alkalinity is a measure of the buffering capacity against the addition of H+. And yes, there is a separate test for this (titration). pH is a measure of the H+ activity. period. From this 'basicity' can be determined, if you know the pKw (ie pOH = pKw - pH)(the pKw shouldn't be assumed to be 14 - it is rare to have standard conditions), but there is no way to determine alkalinity from pH as you need to take into account a wide variety of other ions that contribute to alkalinity (ie At = OH- + HCO3- + CO3-- + B(OH)3 + ...). It is likely that there is a way to measure basicity ( ie [OH-]), though it is presumably much easier to measure acidity ([H+]). Piyrwq 16:43, 12 January 2007 (UTC)
Anybody else have a problem with this statement: "strictly speaking, there is no such thing as the H+ ion"? There certainly is such a thing as the H+ ion. It is called a proton and exists discretely in the in the state of matter known as plasma if nowhere else. If nobody objects, I would like to change this statement to read: "in aqueous solution the H+ ion does not exist independently but is actually the third hydrogen atom in H3O+, called the hydronium ion." Thoughts? Objections? Schlemazl 21:53, 13 February 2007 (UTC)
Also, I'm being driven a little crazy by the addition of "basicity" or "alkalinity" to the definition of pH. Knowing [H3O+] does not mean you know [OH-] (basicity). If you have the literature resources at hand, measured temperature, and know the specific nature of other ions in solution you may be able to calculate basicity from the pH, but one does not define the other. It definitely does not give any insight into alkalinity. For example, it is possible to reduce pH of a solution, through the addition of CO2, while alkalinity remains constant Alkalinity#Addition_of_CO2- alkalinity is absolutely not defined by the log of hydrogen concentration, nor is basicity. These are concepts worthy of much discussion, but are not fitting for the definition of pH. Can we come to some kinda consensus, so that references to basicity and alkalinity can be permanently removed from the definition of pH? Piyrwq 02:41, 14 February 2007 (UTC)
Ok, I have rewritten the whole first paragraph - I hope it is an improvement, but no doubt there is still a lot to be changed. For reference, here is the old version, which I felt was over complicated and too wordy.
pH is a measure of the
acidity and the
basicity/alkalinity of a
solution in terms of
activity of
hydrogen (
H+). In
aqueous solutions H+ ions bind to water molecules forming
hydronium ions, or H3O+. For dilute solutions, however, it is convenient to substitute the activity of the hydrogen ions with the concentration,
molarity (mol/L) of the hydrogen ions (however, this is not necessarily accurate at higher concentrations
[1]
[2]).
In aqueous systems, the hydrogen ion activity is dictated by the dissociation constant of water ( Kw = 1.011 × 10−14 M2 at 25 °C) and interactions with other ions in solution. Due to this dissociation constant, a neutral solution (hydrogen ion activity equals hydroxide ion activity) has a pH of approximately 7. Aqueous solutions with pH values lower than 7 are considered acidic, while pH values higher than 7 are considered basic.
The concept was introduced by S.P.L. Sørensen in 1909, and is purported to mean pondus hydrogenii in Latin. [3] However, most other sources attribute the name to the French term pouvoir hydrogène [4] [5] [6]. In English, pH can stand for "hydrogen power," [4] [5] [6] "power of hydrogen," [7] [8] or "potential of hydrogen." [3] [9] [10] All of these terms are technically correct.
Conrad.Irwin 10:10, 21 February 2007 (UTC)
This is incorrect. In 2000, Jens Nørby, a Danish biochemist, went back to Sørensen's original papers on the subject: "But Nørby traces the 'p' to a simple mathematical convention of naming variables. (...) But he did not give an explicit reason for choosing 'p' in his original two papers. Sørensen was primarily concerned with determining the H+ concentration electrometrically. His central equation involved values for measurements at two electrodes, which he arbitrarily designated p and q. To develop a standard, he set the non-hydrogen component, Cq, at 1.0 and solved for the hydrogen ion concentration, Cp, or 10–p. The number p he suggested calling p+H."
Source: http://www1.umn.edu/ships/words/pH.htm which is a summary of the original article: Nørby, Jens. 2000. The origin and the meaning of the little p in pH. Trends in the Biochemical Sciences 25:36-37. ($31.50) —Preceding unsigned comment added by 75.74.75.149 ( talk) 20:05, 1 February 2009 (UTC)
Regarding "By virtue of its logarithmic nature, pH is a dimensionless quantity." IANACB (I am not a chemist, but..) is it truly because of its logarithmic nature? Wouldn't say, a quantity expressed as "log10 lightyears" still be very much a dimensioned distance? Does the dimensionless of pH perhaps have nothing to do with logarithims and everything to do with the value whose logarithm is being taken? If I'm wrong here, thanks for your patience in considering this. —Preceding unsigned comment added by Dfgriggs ( talk • contribs) 18:22, 22 November 2008 (UTC)
The present intro says, "It is unknown what the exact definition of p stands for. Some references suggest the p stands for “Power”[2], others refer to the German word “Potenz” (meaning power in German)[3], still others refer to “potential”."
To be fair, "power", "potenz", & "potential" are all rough synonyms. Ventifax ( talk) 00:00, 1 April 2009 (UTC)
____________________________________________________________
pH is the abbreviation of the latin expression pondus Hydrogenii (pondus = pressure, hydrogenium = hydrogen) —Preceding unsigned comment added by 165.228.210.24 ( talk) 04:59, 2 April 2009 (UTC)
The article states: Most substances have a pH in the range 0 to 14, although extremely acidic or extremely basic substances may have pH less than 0 or greater than 14. An example is acid mine runoff, with a pH = -3.6. Note that this does not translate to a molar concentration of 3981 M.
But it also states that pH is, strictly speaking, a function of the activity of hydrogen ions in solution, not their concentration. And that is acknowledged by references. Now, a careful look at Wikipedia's article on Activity, or preferably to a Physical Chemistry book, will lead you to see that Activity ranges from ZERO to ONE, and is never higher than one, because pure substances have an activity of 1 by definition (it was meant to be analogued to molar fraction, and molar fraction can never be greater than 1 either).
Now pick a calculator and verify the value of -log(1), the result is 0, and that is the lowest pH a substance can ever have. Strictly speaking, pH can never be lower than zero, except when calculated in a less rigurous way, using molarity or molality: but that is incorrect, and should be pointed out. pH lower than zero may be obtained by other ways, maybe (pH-meter?), but it should be clearly specified how was that value obtained, what does it mean (because if it has no meaning, is serves no purpose and shouldn't be used), and emphasis should be put on that strictly speaking, the pH of a solution can never be lower than 0 (because activity ranges from 0 to 1, and therefore -log(act) ranges from 0 to positive infinity). I'll wait for answers regarding this before modifying the article myself. 158.170.51.28 14:50, 27 December 2006 (UTC)
Was added by User:69.140.68.72 and removed by me. A Google search brings up 20 hits. The top four English resources (disregarding Wikipedia's status as first):
— Edward Z. Yang( Talk) 15:03, 19 February 2007 (UTC)
This article needs a nice image to plaster on the top of the document. One can't really photograph pH, though, so we've got to pick something fairly representative. Candidates:
Possible candidates? (add ones you find to the gallery below) — Edward Z. Yang( Talk) 21:53, 21 February 2007 (UTC)
Not experienced with this, but i cant seem to delete the vandelism :( —The preceding unsigned comment was added by 129.234.4.76 ( talk) 14:50, 24 February 2007 (UTC).
Also there seems to be a discrepancy between tables "Representative pH values[citation needed]" and "pH in body fluids [13]" Apologies if this is in the wrong place but text editing is not my forte. -->Check the Gastric Acid #'s
I propose we semi-permanently semi-protect this article. The amount of vandalism it receives is absolutely ridiculous. — Edward Z. Yang( Talk) 22:36, 1 March 2007 (UTC)
I think it would be interesting to have some biological Ph values for comparison. For example the stomach. Also according to de.wikipedia wine has Ph 4, there is a hole there in the english table. -- 172.174.140.43 07:47, 4 March 2007 (UTC)
I actually wanted to look at the page "pH-imbalance", meaning in the body, but I just got redirected to pH.
If somebody feels up to the job, you might want to incorporate the fact that there are three different scales for pH in place, as a recent discussion on the talk page to the article ocean acidification has showed. Hardern 12:01, 13 April 2007 (UTC)
Two problems with the following:
Firstly, the word lemonade refers to totally different drinks in the UK and USA. The carbonated drink commonly known as lemonade in the UK (and limonade in France) is better known as Sprite in the US, but without the lime flavo(u)r. Secondly, the article does not state whether 0.0050M is a reasonable proton concentration for lemonade - is this a hypothetically concentrated lemonade that nobody would want to drink, or a realistic one? The article on lemons says that pure lemon juice has a pH of 2 to 3, and the article on acetic acid says vinegar has a pH around 2.4. Assuming that lemon juice in lemonade is diluted with about 5 parts water, this would give it a pH 0.8 higher than pure juice - and I would also assume that (American) lemonade is less acidic than vinegar, if sourness is any guide to pH. Mtford 06:36, 10 May 2007 (UTC)
If it's real, it seems that Phidron would be better as part of this article. A search of Google Scholar did not find any references to phidron. Most of those in Google itself are apparently based on this article. ChemGardener 19:55, 28 May 2007 (UTC)
"However pH is actually a shorthand for its mathematical approximation: in chemistry a small p is used in place of writing − log10 and the H here represents [H+], the concentration of hydrogen ions."
My understanding was that the use of p as shorthand to mean -log developed from pH, not the other way around, so I'm pulling this unless someone can source it.
Orange32 03:35, 27 August 2007 (UTC)
I am adding one more question to this. Is it usually written as pH, I mean is 'H' a superscript of p or is it just pH? Elncid ( talk) 12:33, 20 December 2007 (UTC)
This may require a separate article, and I am not an expert (or even proficient) by any means on the following, but the following sections seem to be missing:
Perhaps a separate article may be needed. — Rob ( talk) 20:05, 15 October 2007 (UTC)
Hear, hear. —Preceding unsigned comment added by 58.109.98.211 ( talk) 06:28, 27 November 2007 (UTC)
I don't understand something from this artical, Im a fifth grader so this question must seem stupid to most of you but the less acidic something is like pure water you would say want to put a fish in it, at least someone told me at a feild trip. So you want to put fish in bleach and household lye? —Preceding unsigned comment added by 76.104.227.88 ( talk) 04:23, 29 November 2007 (UTC)
This article is too confusing for someone who just wants a simple explanation of pH. It needs a better introduction and some explanation in words, not just math. —Preceding unsigned comment added by Amberlianne ( talk • contribs) 03:22, 9 March 2008 (UTC)
I wholly agree with this. pH is just a simple acidic calculator, not 10 mathematic equations which have nothing to do with acids and science. Same with Circumference. Koshoes ( talk) 18:54, 25 January 2009 (UTC)
Indeed! I have a PhD in Computer Science and informal Chemical education, and I find this article level totally inappropriate. I think the "solution" is to split it into an "Exact definition of pH for Chemical Engineering" and keep "pH" as a high-school grade article which does not make references to "activity" at all. A basic article on pH should follow most biology/chemical 101 text, defining it as -log [H+] using molarity, and giving specific examples of actual pH and its importance to the human body and simple solutions (eg swimming pools, fish tanks, etc)
see for exmaple http://antoine.frostburg.edu/chem/senese/101/acidbase/faq/what-is-pH.shtml
Is there a simple way for the article writers and editors to state plainly the question, "What is pH?" 70.231.150.141 ( talk) 02:11, 19 March 2008 (UTC) In a simple way for any range of high school student down to elementary school student to understand? Thanks. 70.231.150.141 ( talk) 02:13, 19 March 2008 (UTC) Wait, I'll post it as best as I can. —Preceding unsigned comment added by 70.231.150.141 ( talk) 02:14, 19 March 2008 (UTC)
I think the article would be clearer if we dropped most references to hydronium ions (H3O+) in favour of hydrogen ions (protons, H+).
When you consider the solvation, H3O+ isn't all that accurate anyway - it's more like H9O4+ but this depends on temperature. So H3O+ isn't much more accurate as a description of what protons do in aqueous solution than writing H+ (aq). However, writing H+ is much simpler and scarcely less accurate.
Ewen ( talk) 08:33, 23 March 2008 (UTC)
Reworking the introduction section somewhat, how does this sound?
I've tried to limit the hydronium ion stuff (not least because the hydrogen ion pages points to other hydrates of protons, and implies that "hydrogen ion" is favour by IUPAC), and have broken the text up into several more readable (to me) paragraphs. I've also extended the mention of acids and alkalis, since this seems pretty important to me.
Anyway, I'm no chemist, so may have botched some of the above. Comments welcome. If I don't hear anything at all, I'll replace the current intro with the above. Cheers, -- Plumbago ( talk) 16:05, 4 April 2008 (UTC)
The assertion that pure water is pH 7 will confuse budding experimentalists who find that their "pure" water is acidic. Perhaps it would be appropriate to mention that pure water exposed to the atmosphere becomes acidic as CO2 combines with water to form carbonic acid. This is often a point of confusion as folks are experimenting with pH. JonMoulton ( talk) 20:36, 8 April 2008 (UTC)
In text: "But here we define a strong acid as a species which is a much stronger acid than the hydronium (H3O+) ion. In that case the dissociation reaction (strictly HX+H2O↔H3O++X− but simplified as HX↔H++X−) goes to completion, i.e. no unreacted acid remains in solution"
Dissociation ?
Contributions from Brazil
user:pt:lemarlou —Preceding unsigned comment added by 189.68.63.196 ( talk) 15:05, 11 April 2008 (UTC)
There are two tables in this article. One places gastric acid at 1.5-2.0, the second places gastric acid at 0.7. Which is correct? -- Arperry ( talk) 22:28, 29 July 2008 (UTC)
I find it a little sad that both the article and the talk page currently fail to include the string "volt". So, well, at least the latter I can remedy:
At 293.15 K, a pH difference of 1 corresponds to a voltage of .05817 V, or ln(10)× R×293.15 K/ F precisely. For other temperatures, modify accordingly.
That much I am able to gather from the definition given on the page. pH meter appears to have slightly more, but could the relationship between pH and voltage on the one hand, and pH and temperature on the other hand, be made clearer to the non-experts among us?
Is it really as simple as saying that a voltmeter will display pH differences, if temperatures are constant, in the ideal case of an infinitesimal test charge being used?
RandomP ( talk) 13:51, 18 August 2008 (UTC)
http://en.wikipedia.org/wiki/Talk:PH A recent news article claimed that a pH change of as little as 0.02 units could significantly change the degree of absorption of sound in seawater, especially at low frequencies. [3] Do small pH changes also affect the speed of sound in water? To illustrate, picture a large explosive sitting on the ocean floor, and far above it a net of electrodes establishing a steady pH gradient, or a net of tubes emitting fluid of high/low pH, or a large wrapped isoelectric focusing gel... when the target sub passes overhead, the sound of the blast is refracted by differences in transmission speed, and a significant fraction of the original blast is reconstituted at the distant focal point. Or not? ;) Wnt ( talk) 17:55, 3 October 2008 (UTC)
The pH scale images are too small to interpret from the page. This would render them totally useless in printed versions. Can we get them scaled up, please? -- IronMaidenRocks ( talk) 19:02, 7 November 2008 (UTC)
Doesn't pH only go down to 0? Why does the chart say -1? Shouldn't it be edited and or deleted? I have been taught and can find no source contradicting the fact that pH goes down to 0. —Preceding
unsigned comment added by
68.33.178.97 (
talk)
04:55, 20 January 2009 (UTC)
Possibly better pH chart here:
pH chart I created it and am very open to suggestions for change. --
Hansepoo (
talk)
02:57, 8 July 2009 (UTC)
In Chemistry class today, when we were talking about the pH scale, I thought of a problem: If the concentration of H+ or OH- is less than 10-7M, taking the logarithm will result in it being over 7, which does not make sense, since how could an acid be diluted so much that is becomes a strong base, or vice-versa? I didn't see anything about it here, nor in the Chemistry book I looked at to find an answer, anyone have an explanation? -- Gimmethegepgun ( talk) 16:47, 11 March 2009 (UTC)
pH is defined as minus the decimal logarithm of the hydrogen ion activity in an aqueous solution. [15] By virtue of its logarithmic nature, pH is a dimensionless quantity.
where aH is the (dimensionless) activity of hydrogen ions. The reason for this definition is that aH is a property of a single ion which can only be measured experimentally by means of an ion-selective electrode which responds, according to the Nernst equation, to hydrogen ion activity. pH is commonly measured by means of a combined glass electrode, which measures the potential difference, or electromotive force, E, between an electrode sensitive to the hydrogen ion activity and a reference electrode, such as a calomel electrode or a silver chloride electrode. The combined glass electrode ideally follows the Nernst equation:
where E is a measured potential , E0 is the standard electrode potential, that is, the electode electrode potential for the standard state in which the activity is one. R is the
gas constant, T is the temperature in Kelvin, F is the
Faraday constant and n is the number of electrons transferred, one in this instance. The electrode potential, E, is proportional to the logarithm of the hydrogen ion activity.
-- Mrfabioc ( talk) 19:06, 3 May 2009 (UTC)
The article states that carbon dioxide is an acid, but is it right to say this? My understanding is that carbon dioxide will dissolve in water to give an acidic solution of carbonic acid, but then carbonic acid is the acid, not carbon dioxide. Baclough ( talk) 10:34, 24 May 2009 (UTC)
The article says that, "The pH for pure water at 25 °C (77 °F) is close to 7.0.". I don't think that that is true. Pure water should always have a pH of 7, no matter the temperature. Please tell me if I am wrong. Nathan.tang ( talk) 11:11, 13 July 2009 (UTC)