Talk:PH/Archive1

From Wikipedia, the free encyclopedia

This 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.

Old comments

We have a fine article on PH here-- but it doesn't say what the P and the H stand for!

AFAIK there is also pOH, in a sense the opposite of pH, which measures the concentration of OH- ions

pH

What is the pH of 4% Hydrochloric acid?

I doubt Wikipedia is the right place to ask that question. You might try in the newsgroup sci.chem... -- Schnee 17:48, 21 Sep 2003 (UTC)

the letters 'p' and 'H'. There is little debate that the H stands for Hydrogenium. However, the widely held belief that the 'p' stands for potential (Potenz / puissance / potentia / pondus) has been questioned by Jens G Nørby in an article in Trends Biochem. Sci., 2000, 25(1), 36-37. It appears that the letter 'p' stems rather arbitrarily from a derivation by S.P.L. Sørensen of the electric potential of an electrode for measuring the H+-concentration.

By the way, formally the definition of pH as -log [H+] is not correct, seeing as [H+] is not dimensionless. Rather, it is defined as -log ([H+]/[H+]ref) where [H+]ref is 1 mol/l. --Watje22 09:27, 3 August 2005 (UTC)

It would also be more accurate to define pH in terms of hydrogen activity as opposed to hydrogen concentration, this can be a very important difference in some systems (Seawater for example). --Piyrwq 02:15, 15 August 2005 (UTC)

Title

Is it possible to name the article 'pH' as opposed to 'PH'?

No, it's a limitation of MediaWiki as it's being used here. It's probably the most annoying of the ones on Wikipedia:List_of_pages_whose_correct_title_is_not_allowed_by_MediaWiki. -- User:Docu

Range

"In layman's terms , the "pH" value is an approximate number between 0 and 14..."

I'm pretty sure that the pH can fall outside the range 0 to 14. Maybe they meant that it usually falls in this range. I've worked with 18 M sulfuric acid, and I'm pretty sure that stuff had a pH < 0. Maybe someone could correct this.

I'm quite sure that pH cannot exceed this range. 0 means it has no hydrogen ion (H⁺) concentration, and only hydroxide ion (OH^-) concentration, which cannot be possible. That's as it says in a college biology textbook. See http://www.google.com/search?hl=en&lr=&client=firefox-a&rls=org.mozilla:en-US:official&oi=defmore&q=define:ph for more websites on this topic. --Bsdlogical 17:54, 11 Dec 2004 (UTC)

The pH scale is a logarithmical scale, so sub-zero values are neither impossible nor strange, just unusual. —Caesar 23:35, 2004 Dec 15 (UTC)

Nonsense. Expression -log(c) is negative just for c>1. And c is the H₃O⁺ concentration which evidently cannot exceed 100%, therefore pH cannot be negative. And pH>14 is nonsense for the same reason, since the product of H₃O⁺ and OH^- concentrations in aqueous solution is constant — 10^-14. So pH>14 would indicate the concentration of OH^- greater than 100%. The pH>14 can be achieved only in other than aqueous solutions, where the constant is different from 10^-14. Negative pH definitely doesn't exist.

-- Egg 22:42, 2004 Dec 16 (UTC)

Oh, I'm sorry. My basic presumption that c cannot be >1 is wrong, so the pH eventualy could be out of the 0-14 range. But in fact the definition of pH uses ion activity instead of concentration and that is k times concentration, where k<1. And the ions become inactive in high concentrations, therefore pH really doesn't exceed nor 0 nor 14.

-- Egg 00:47, 2004 Dec 17 (UTC)

But don't forget, that concentration is not percentual, but molar. The "concentration of water in water" therefore is not 1, but approx. 56 mol.dm^-3. If we imagine hypothetic situation, that we have the 1:1 mixture of H₃O⁺ cations and X^- anions of the same molar weight, we get pH = -log 28 = -1.4 . I'm not taking into account activity, I just wanted to show that the limitation is not related to K_w. —Mykhal 01:39, 20 Dec 2004 (UTC)

I hope it will finish discussion about possibility/impossibility

pH - is just a function of activity of hydrogen ions, pH= -1 means that you have activity of hydrogen ions equal 10 mol per liter. It is definitely POSSIBLE if you work with high concentrations of acid solutions like H2SO4. pH=15 means that you have activity of OH-ions equal 10 mol/l (or if you want to recalculate into hydrogen ions activities for aqueous (!) solution = 10^-15 mol/l). It is also definitly POSSIBLE when you work with high contration alkali solutions like NaOH or KOH. DO NOT use percent concentration, ONLY molarity. Please, stop these funny discussions about possibility - impossibility. (Kaverin)

CO₂

I've read, here and there, mainly on equipment for pH balancing, stuff that suggests that there's a relationship between pH and CO₂.

Anyone got a minute to explain why higher CO₂ should lower pH? Should an over-planted aquarium see a really high pH?

look at hydrolisys

CO₂ + H20 -> H⁺ + HCO₃^-

(Kaverin)

Degrading plants will generate CO₂ and H⁺, this will serve to lower the pH. Thriving ::plants(ie photosynthesizing) will consume CO₂ and H⁺, thus raising your pH. Net results ::depends how well your plants are doing I'd think.

(Piyrwq)

The trick is that CO2 reacts with water to form carbonic ACID, which then dissociates:

C02 + H2O --> H2CO3 --> HCO3- + H+

It's actually one of the ways that our body maintains blood pH... Therefore, a person with lung difficulty such as cystic fibrosis, will also suffer from acidosis, due to an inability to get rid of CO2 in the blood...

-wedgeoli-

'Neutral' substance

Is the statement that "the only neutral substance is distilled water" correct? If neutrality is simply pH=7, then it's trivial to create a "neutral" solution that isn't distilled water. For example, add baking soda to water to raise the pH. Then, add just enough vinegar to make the pH=7. The water is neutral (pH=7), but isn't distilled, either. Perhaps we are confusing "neutral" with "pure?"

I think this is important to clarify, especially since the article calls this out as being "important to note."

The scale shows pure water as having a pH of 7.0. But this cannot be correct. Pure water contains no ions at all as the water molecules only disocciate when impurities are present. Thus a logarithmic scale of ion concentration cannot be applied to a substance that has no ions. Deionised water is the purest that can currently be obtained (the clue is in the name). It is impossible to measure the pH of deionised water because the indicator itself plus its solvent introduces ions in the same quantity as water that disocciates and thus invalidates the results because all the ions are introduced by the measurement method. Similarly, an electronic pH meter's indication is useless because the pH electrode relys for its operation on a conductive sample, something that deionised water most definitely is not. In fact deionised wter will degrade a pH electode because it has an enormous affinity for ions and will 'suck' them out of the electrode.

...Incidentally, pure distilled water, when exposed to the atmosphere, has a pH of 5.7, due to carbon dioxide ingassing.

But this doen't occur instantly.

Agree on both points. Note removed. Vsmith 00:47, 27 Feb 2005 (UTC)

Cancer patients

The table claims that cancer patients have a significantly lowered saliva pH. I'm sure this is only true for a few types of cancers, if at all. Do we have a reference? AxelBoldt 20:53, 26 May 2005 (UTC)

It is heavily claimed that people with cancer have a more acidic pH. This hasn't been very well documented, but there have been smallish studies (I can't find a link).

This should be removed again unless someone can come up with a decent reference. Piyrwq 18:25, 12 June 2006 (UTC)

Removed. Besides, it did not have the proper colors on the background. Be bold! vidar lo 22:49, 12 June 2006 (UTC)

pH Definition

I re-jigged part of the pH definition in an effort to get away from this re-occuring idea that pH is somehow an exact number between 1 and 14. For example, the pKw isn't even really 14, it's 13.995. By pointing this out maybe people won't get so caught up in some of these 'laymen' definitions.

I'm still not very happy with my wording though, and will likely reword a few things soon if someone else doesn't do it first. Piyrwq 14:47, 19 August 2005 (UTC)1

pH terminology

The statement "The p stands for the German Potenz" is a myth and should be removed. Sorensen arbitrarily chose the letters p and q for two solutions in his paper. The term pH is derived from solution p with the unknown concentration of H+ ions. Mr. Davies class hates ph scale.

Reference: Norby JG "The origin and the meaning of the little p in pH" Trends Biochem Sci. 2000 Jan;25(1):36-7

pH=power of potential of hydrogen [1] Medscin 17:50, 2 January 2006 (UTC)

Units and formula

pH value has no unit.

Not strictly true: its units are $l o g 10 m o l . d m - 1$ which is not dimensionless at all, just a very weird dimension. Very weird is not the same as none.

pH = − log10[H + ]

I changed it to the more traditional formula, because the following text refers to that formula. If u want to add the more accurate formula, put it elsewhere and explain the difference.

--대조 | Talk 20:40, 15 January 2006 (UTC)

Referring to the formula $\mbox{pH} = -\log_{10}\left(\frac{\left[\mbox{H}^+\right]}{\mathrm{mol}\cdot\mathrm{dm}^{-3}}\right)$

- isn't something on the bottom of an equation with a negative coefficient the same as on the top line with the negative dropped, so shouldn't it be

$\mbox{pH} = -\log_{10}\left(\frac{\left[\mbox{H}^+\right]}{\mathrm{mol}\cdot\mathrm{dm}^{3}}\right)$

Just for the sake of clarity: a logarithm is always dimensionless, even if it is a logarithm of something with dimension, see below!! If the logarithm is lower than 0 this does not mean that is is a logarithm of something that is lower than zero, it is the logarithm of something between 0 and 1. Logarithms of negative numbers only exist if you are using the complex number system! (signed Lave Fischer)

why 'pH scale'???

having spent an hour trying to find this out as part of my chemistry homework, i still have absolutely no idea as to the word that the name 'pH' is derived from!!! according to my chemistry teacher it's a German word, but i am still completely clueless as to what this word is. if anyone knows, could they please post it, as i know you are all highly intelligent people.

Thanks--XMagicFairyX 19:25, 6 February 2006 (UTC)

There's a bit of confusion across the web on this. The two I've seen are French and Dutch (the Dutch one might be the one you're looking for). The French one, however, is more commonly accepted (that's what my textbook says). This is a question for Wikipedia:Reference desk — Edward Z. Yang^(Talk) 00:14, 7 May 2006 (UTC)

Acid Rain

Acid rain is any type of precipitation that has got a pH which is lower than 5.0. Please put another example for pH 6.0.

that box to the right

How is it edited? Redox should not be in the box about acid-base chemistry. Olin 22:26, 19 February 2006 (UTC)

I find that redox-ractions is somewhat related to acid-base, and thuse appropriate. So I think it should stay. --vidar lo 10:59, 6 March 2006 (UTC)

negative pH

Battery acid -0.5 Does it mean that [H+] is larger than one? Or is it a mistake?

No, it's not a mistake. 10 to 0.5 is about 3.2 mol/L. Space Cadet 01:07, 28 February 2006 (UTC)

On negative pH, there is the sentance "An example is acid mine runoff, with a pH = -3.6. Note that this does not translate to a molar concentration of 3981 M." Well, what does it translate to!? According to the simple log function for pH, this is the result you would get. Some clarification is needed here. eprigge 12:57, 20 October 2006 (PST)

You have to factor molecular activity. I'm not familiar enough with the mathematics/equations to give you an exact number though. — Edward Z. Yang^(Talk) 02:51, 21 October 2006 (UTC)

negative pH in aqueous

is negative pH possible to create in an aqueous solution. i know it is certianly possible to have negative pH with strong acids. but is it possible to prepare it in water if it is limited by Kw? also, is a high pH possible to prepare (>14)?

Yes, it is possible to prepare it in water because your [OH] will be less than 10 to -14, so multiplied by each other they will give the exact Kw. As far as > 14, your everyday "Liquid Plumber" has pH of about 15. Space Cadet 12:15, 27 February 2006 (UTC)

Math formulas.

I've started cleaning up the math formulas in this article, as some of them is written in html. This defies the point of letting the user choose whatever to display as png, html or MathML. All formulas should be written in LaTeX. Further, should we use $\lg{\left[H_3O^+\right]}$ or $\log{\left[H_3O^+\right]}$ ?--vidar lo 10:58, 6 March 2006 (UTC)

Well, since mathematicians get all scuffly when you use log to mean base-10, I'd say

log 10 [H 3 O +]

is our best bet. — Edward Z. Yang^(Talk) 00:17, 7 May 2006 (UTC)

title

what happened to that "technical restrictions" thing? How come I see two titles, pH and then underneath PH.

long term effects of elevated pH in living orgqanism

In plants I understadn that high ph blocks the absorption of nutrients - What does it do to animal life?

this will often stop the stop the spawning of fish eggs

Absolute value on concentration

User:Hdante recently reverted the pH equation to this form:

$\mbox{pH} \approx -\log_{10}{\frac{[\mathrm{H^+}]}{1\, mol/L}} = -log_{10} {|[\mathrm{H^+}]|}$

I find the addition of the absolute value signs quite puzzling: isn't concentration always positive? (I suspect that I am misinterpreting the meaning of the straight bars) Furthermore, because brackets denote concentration/molarity in mol/L, wouldn't dividing by 1 mol/L make the concentration unitless? I mean, pH is a unit-less scale, but I would think it would be improper to remove the units from inside the equation...? Someone please explain this to me. — Edward Z. Yang^(Talk) 15:50, 14 May 2006 (UTC)

This is mathematical bureaucracy, required to give the complete insight of the equations. The first point is that you shouldn't take the log of a number with a unit. The second point is that the activity aH+ is unitless, so that it can't be formally compared to something that has a unit (apples X oranges). The last point is that the equation aH+ = [H+]/1molL-1 defines the scale of aH+, that is, it is unitless, but its value is numerically equal to the concentration (in whatever units you'd be using). The last equation, pH = -log |[H+]| means "when calculating the log, don't take into account the mol/L thing", ex: pH = -log |1e-7 mol/L| = -log (1e-7). A similar equation is used in the german wiki. --Hdante 16:57, 14 May 2006 (UTC)

Aha! Suddenly it makes sense. Thanks for the clarification. Maybe a footnote's in order? — Edward Z. Yang^(Talk) 00:21, 15 May 2006 (UTC)

Hello. I think an example is better than a footnote. What's the pH of a lemonade ? --Hdante 19:08, 16 May 2006 (UTC)

Depends on the lemonade. There is a list of pH for some common products, and that should do. Most people should be able to relate it to that list... But it is a logaritmic scale, so I'm not so sure anyone will understand that too easily. Maybe a simple chart with the concentration of

H +

vs. the pH would do? I'm gonna make one soonish... vidar lo 07:57, 18 May 2006 (UTC)

The use of the absolute value is nonsense. First: the absolute value of a unit with dimension is not in general dimensionless. The reason that pH is dimensionless is that it is a logarithm. There is absolutely nothing to stop you from making the logarithm of a unit with dimension, but the logarithm is dimensionless all the same. (An easy way of "demonstrating" this is to make the differential of a (natural) logarithm: d ln x = dx/x, from which you see that the units cancel and the logarithms are always dimensionless, all logarithms irrespective of base). So remove the nonsense about absolute value someone who is authorized, negative activities do not exist. Signed: Lave Fischer

pH indicator's color range

Can someone please explain to me how one might determine the pH at which an indicator changes color?

Your question should be directed to the reference desk in the future. However, I'll indulge you. Read pH indicator to find out more on what indicators really are, and then think logically. If the pH indicator's pH change is known and we use it to determine the unknown: the pH of the solution, what if the pH of the solution is known? — Edward Z. Yang^(Talk) 20:50, 23 May 2006 (UTC)

Number of Hydrogens?

Is pH basically the number of hydrogen ions in a solution? The higher the number of hydrogen ions the greater the pH and the more basic?

If so the why would amino acids lose Hydrogen ions in a high pH solution if there is a greater concentation of H outside the amino acid envrionment?

Am i making sense and have i got it all wrong? Thanks in advance.

When asking questions like these, please use the reference desk in the future. However, I'll give you two terse answers: yes except in extremely concentrated solutions and no you've got it reversed. — Edward Z. Yang^(Talk) 13:34, 30 May 2006 (UTC)

Can we have a explanation of 'pH' in laymen's terms?

Can we have a explanation of 'pH' in laymen's terms? Doesn't need to be a long thing just a paragraph or two. I don't know this stuff real well. :)

Well, the first paragraph should be in laymen's terms. What do find about it that's hard to understand? — Edward Z. Yang^(Talk) 20:52, 31 May 2006 (UTC)

Question:

Why don't create a link to know what the ionization constant od water is!

Self-ionization of water, which is on the menu at the top of the article. — Edward Z. Yang^(Talk) 19:31, 8 June 2006 (UTC)

pH itself

the H is for hydrogen. What does the p stand for? Simply south 21:18, 13 June 2006 (UTC)

See last paragraph of the introduction. —Keenan Pepper 22:22, 13 June 2006 (UTC) (slightly edited by — Edward Z. Yang^(Talk))

Whoops. My mistake. Simply south 12:10, 14 June 2006 (UTC)

I removed "potential hydrogen" from the first sentence. Users must read the entire paragraph to find out the literal meaning of p and H, if there is one. There must be a better layout for this.--Merlin002 11:36, 26 July 2006 (UTC)Hal Avisado

Activities have units!!!

Apparently quote: "aH+ denotes the activity of H+ ions, and is unitless."

This is a fundamental error commonly encountered amongst lower second class (2:2) undergraduate students. Activities are defined as being linearly proportional to concentration (which has UNITS), the proportionality constant being dimensionless and usually represented in the literature as "gamma". This dimensionless constant is often the source of confusion amongst weaker students who confuse an "activity" with an "activity coefficient". For the equation to be dimensionally meaningful it must have a consistent set of units. Therefore activities HAVE UNITS!!!!! Furthermore the original author of this erroneous entry confuses the issue further because the definition given is of a logarithmic nature where any accountability of units is lost by "logging". Worst still the pH scale as defined by it's founder Sören Sörensen in terms of concentrations NOT activities.

Get it right!!!

aH+=gamma(H+) * [H+]

—Preceding unsigned comment added by Oxford chemist (talk • contribs)

Yes, but you should sign your comment, and remove offensive language from it. Stay civil. Please correct the article in question. Be bold!

09:40, 29 June 2006 (UTC)

—Preceding unsigned comment added by Vidarlo (talk • contribs)

Hey hot shot, if you want to define pH for us, why don't you do some research first. I know of at least 4 defintions you can look up; you can start with some history here:

Sorensen, S.P.L., 1909. Enzymstudien. II. Mitteilung. l]ber die Messung und die Bedeutung der Wasserstoffionenkonzentration bei enzymatischen Prozessen. Biochem. Z., 21: 131-304.

and here:

Sorensen, S. P. L.; Linderstrom-Lang, K. The determination and value of po in electrometric measurements of hydrogen-ion concentrations. Compt. rend. trav. ab. Carlsberg (1924), 15(No. 6), 40 pp.

and some more modern stuff here:

Dickson, A. G.. pH scales and proton-transfer reactions in saline media such as sea water. Geochimica et Cosmochimica Acta (1984), 48(11), 2299-308

and here:

Dickson, Andrew G.. The measurement of seawater pH. Marine Chemistry (1993), 44(2-4), 131-42

I'm sure you'll notice in the Dickson (1984) paper that sorensen in fact attempted to defined pH as a function of Hydrogen activity in 1924. And if you think Dickson is an idiot too I recommend you brush up on your German. Good luck! Piyrwq 15:38, 29 June 2006 (UTC)

Okay, uhm, can we all try to stay civil and assume good faith, here?

At least one of the points Oxford chemist raises is entirely valid: The sentence

Though a pH value has no unit, it is not an arbitrary scale

is just a bit weird: the numeric value of something measured in a unit, such as the pH value, is measured on an arbitrary scale.

In fact, a correct sentence would read something like

Since the definition of a pH value involves a choice of units, it is an arbitrary scale

I don't know about the activity vs concentration issue, but I do know enough to say that the article as it stands is inconsistent.

Note that, as has been pointed out above, the unit of the pH value is the rather weird $\log_{10}(\frac{mol}{l})$ — if you use other units than mol or l, the effect will be a shifted scale, not a rescaled one; if you use another base than 10 (and there are very very good reasons to), that will cause a rescaling.

And given the widespread use of scientific notation today, one must wonder why some people apparently think "a pH value of 7" is a better expression than " $10 - 7$ mol/l of H⁺", which not only is similarly short but avoids having to define the pH scale in the first place.

From a non-chemist POV, it all looks very weird. RandomP 13:51, 2 July 2006 (UTC)

Also note that mole fraction contains a similarly weird section:

All of the preceding numbers are dimensionless. Other ways of representing concentrations, e.g., molarity and molality, yield dimensional quantities (per litre, per kilogram, etc.). When chemical formulas seem to be taking the logarithms of dimensional quantities, there is an implied ratio, and such expressions can always be rearranged so that the arguments of the logarithms are dimensionless numbers, as they must be.

I'm hoping someone more knowledgeable than me about chemistry can give this a shot? RandomP 14:38, 2 July 2006 (UTC)

Acording to P. Atkins and L. Jones, in Chemical principles: the quest for insight, chapter 9

"In this expression, $a j$ is the activity of substance J. For ideal systems, that we consider, the activity has simple meanings: (...) For a diluted solution, $a j$ is the numerical value of molarity, $a j = [J]$ (sidenote: similarly, more formally, $a j = [J] / (m o l . L - 1)$ ). (...) Note that all the activities are numbers: they don't have unit. For real systems, the activity is not exactly equal to pressure or molarity and we write: (...) for a solute J, $a J = γ j [J]$ "

Then we understand what the English Chemist up there was talking about. He was so used to the informal equation of activity, a = [J], that he took it for granted. Then he just skipped to the "advanced" gamma equation, to say that only gamma is adimensional, not the activity. Too bad, Oxford Chemist. If he'd just realized that

l o g (a)

would be impossible if a were not a number, maybe he would realize the low rigour in which Chemists use mathematics. Atkins is from there, Oxford. It's obvious that you didn't take classes with him. --hdante 02:24, 31 July 2006 (UTC)

Categories: Talk archives