Talk:Solubility equilibrium

If you edit the table

Note to anybody editing the table: If you add a line to the table, or change a line, please be sure to cite your data source. Various sources disagree when it comes to solubility product data. Hence without citing a source, any data placed in the table is meaningless. The table has a data source column for that reason. Karlhahn 22:47, 13 December 2006 (UTC)

Wikify

Not bad. I'm going to do some editing myself though, to Wikify a little and also perhaps get things that don't always dissociate completely and so readily as sucrose (maybe an organic acid). Its certainly better than before. EagleFalconn 20:45, 7 Dec 2004 (UTC)

I like it, but it does seem to leave out solid state chemistry. I don't see an obvious way to fix that now, but perhaps I'll come back to it. Articles such as precipitation strengthening could use a link here; I'll work on that for now.--Joel 03:58, 5 August 2005 (UTC)

== merger ==

I put the merger notice; is there really a good reason to have a separate solubility equilibrium article than solubility. There seems to be a lot of overlap in both. Olin

Seems a reasonable suggestion, although I think eventually we will need a separate article on solubility product constant. Until that gets written, all of this could be a section of solubility. Walkerma 19:19, 27 February 2006 (UTC)

I was just thinking about writing a solubility-product constant article when I found this. I think I might, don't know if I'll get around to it tonight, but hopefully soon. seanm028

I suggest keeping it separate, simply because it also has some overlap with equilibrium. Keeping them separate is useful for people interested in equilibrium, and not solubility in general. Pwnz0red

try to think BIG, keep the articles separate, the content will evolve (for example solubility constant table ). Also scope solubility is larger should include solubility of gases in liquids and solids in polymers etc. V8rik 00:17, 26 March 2006 (UTC)

I realize the merger was rejected (although more by non-votes than actual votes), but I will express my opinion more completely, and let the crowd decide. I still don't understand the allure of having two articles. Solubility equilibrium is always associated with solubility, and is a proper subtopic. There are a lot of chemistry articles that are quite fragmented, and it would be nice to have some larger, coherent articles.

Furthermore, why should solubility have a solubility equilibrium article? Should we have an electron transfer equilibrium article and a redox reaction article? If you were looking in an encyclopedia, would you really look up solubility equilibrium? (The solubility of gases in liquids and other above solubilities are equilibrium processes.) I will admit, there is no Wikipedia policy to go by here (just my opinion!), and hence I will let it lie, but I just wanted to express my opinion more completely. Olin 20:40, 28 March 2006 (UTC)

Merge with chemical equilibrium instead

I think that solubility equilibrium should merge with equilibrium constant, and that page should have a solubility product constant inside the solubility equilibrium section. In fact, I was going to link to it in my post on the discussion of the redox page. Kr5t 02:36, 29 March 2006 (UTC)

• not merge: in the interest of quality of information flow and ease of navigation this type of merged should not take place, after all these are not identical topics but related topics. The article chemical equilibrium should be a qualitative article about equilibria. From this article you get to equilibrium constant and to solubility constant and acidity constant and it also makes sense to keep general introductionary text separated from text treating the mathematics and piling many topics on top of each other does not help anybody V8rik 19:02, 29 March 2006 (UTC)

• 'do not merge see below Anlace 15:02, 10 June 2006 (UTC)
• 'opposed Each chemical constant needs its own article because the system of dealing with each one is fundamentally different but based on the same rules, mixing them together will confuse people. —Preceding unsigned comment added by 83.42.216.20 (talk) 17:46, 30 January 2008 (UTC)

Merge unless...

I believe the pages should be merged. Solubility equilibrium is directly linked to chemical equilibrium and should be placed on the same page in its own sub-section. If, however, someone is to create a comprehensive solubility equilibrium constant table, the page should remain as it is. marcpatt14, May 2006

strongly oppose merger. these are both big topics and very different topics. if anything we need more articles such as total dissoved solids, a major topic in water quality analysis within environmental science Anlace 15:01, 10 June 2006 (UTC)

Table

The following is a rough draft of a sol-prod table (from Lange's and CRC) that I will be adding to the article once I've finished proofreading it Karlhahn 01:34, 28 August 2006 (UTC).

Table has now been moved to main page Karlhahn 01:15, 30 August 2006 (UTC)

Doesn't give correct formulæ for hydrated compounds. —DIV (128.250.80.15 (talk) 08:49, 5 April 2008 (UTC))

Clarity

A casual observer may struggle to understand whether a compound with a high or low solubility constant was the most soluble. Does a high solubity constant indicate the most soluble? Maybe this should be clarified.King of Leon 16:57, 9 May 2007 (UTC)

      ---- indeed it does, if the solubility is greater than 1 its very very soluble, if it has less than 1 its less soluble most substances have a very low solubility < 10^-5 . but yes a higher Ksp means more solubility less Ksp means more insolubility

Equations

The development of the solubility product equation for CaSO4 is unclear. All of a sudden K is under square root, but no explanation of how it ends there.

This becomes clear below, however that equation as well or rather its development is also unclear. I think this article is very important but needs a lot of help.--Goobysam (talk) 20:56, 7 January 2009 (UTC)

wikipedia contradicts itself

umm, i was looking up the accepted K_sp value for Ca(OH)₂ for a lab, and i noticed wikipedia gives 2 values for it, 4.68 × 10−6 on the Calcium Hydroxide page, and 8.0 × 10−6 on the chart on this page. which one would be correct? these things should be looked into in order to remove discrepencies.74.104.255.195 23:41, 17 May 2007 (UTC)

The different numbers came from different sources, and different investigators have come up with different numbers. The solubility equilibrium table cites a source. The calcium hydroxide page does not. [1] and [2] both give still other values. I have added a line for one of the above sources. Karl Hahn (T) (C) 00:54, 18 May 2007 (UTC)

alright thankyou74.104.255.195 21:34, 19 May 2007 (UTC)

Units

it seems that the units are missed out throughout the context shouldn't solubility products have the units like mol dm^-3, mol² dm^-6, mol³ dm^-9, etc (depending on the number of ions in the compound)218.215.27.145 13:19, 20 June 2007 (UTC)

Complex Ksp

I added a section on if the mole ratios are not even. it needs a little tidying up but the facts are solid hope someone finds it useful. —Preceding unsigned comment added by 83.42.216.20 (talk) 17:42, 30 January 2008 (UTC)

Thank you very much for that. I went through it and (hopefully) beautified it a bit. I also tried to clarify the units as much as I could. Hope I did not thoughtlessly affect your favourite bit in this nice and useful equation of yours. Stan J. Klimas (talk) 12:41, 1 February 2008 (UTC)

nope not atall you did a great job, thanks. —Preceding unsigned comment added by 88.24.15.38 (talk) 19:05, 26 May 2008 (UTC)

How about explaining how the equation is derived? I can't arrive at this equation.220.255.4.133 (talk) 17:38, 13 August 2008 (UTC)

Ill put up a derivation. —Preceding unsigned comment added by 82.1.253.112 (talk) 22:08, 21 November 2009 (UTC)

general formula

I think that the general fomula

${\sqrt[{n}]{K_{\mathrm {sp} } \over {x^{x}\cdot y^{y}}}}={C \over M_{M}}$

is wrong. I don't know where it comes from.

The solubility product for a general binary compound A_pB_q is given by

K_sp = [A]^p[B]^q

When the product dissociates the concentration of B is equal to q/p times the concentration of A.

[B] = q/p [A]

Therefore

K_sp = [A]^p (q/p)^q [A]^q

= (q/p)^q × [A]^p+q

The solubility is 1/p [A]

$[A]={\sqrt[{p+q}]{K_{\mathrm {sp} } \over {(q/p)^{q}}}}$

The above does not incorporate the last step: the solubility is the mass concentration in terms of the solid. One may incorporate 1/p and insert it under the root to obtain:

$S={[A] \over p}={[B] \over q}={\sqrt[{p+q}]{K_{\mathrm {sp} } \over {(q/p)^{q}}p^{p+q}}}$

Then simplify the powers of p and q. Then convert the molar concentration to the mass concentration and you might find that the original formula is correct after all. Hope this helps. Cheers. Stan J. Klimas (talk) 13:15, 2 July 2010 (UTC)

Many thanks for this; is it worth putting in the main text? I want to go over this article. In particular, the treatment of activity is unsatisfactory. Petergans (talk) 06:26, 3 July 2010 (UTC)

I think that the current text could use improvements, including the addition of the derivation because this formula is not found in the English-language textbooks I am aware of. If German wikipedia is accurate, then the formula should be found in the following textbook, which I do not have: Jander, Blasius: Einführung in das anorganisch-Chemische Praktikum. S.Hirzel, Leipzig 1995 (14. Aufl.), ISBN 3-7776-0672-3. Cheers. Stan J. Klimas (talk) 14:01, 3 July 2010 (UTC)

Extensive revision

The text has been extensively revised and new sections added. There is overlap with the article solubility, but my feeling is that there is no need to merge these articles. Petergans (talk) 08:43, 7 July 2010 (UTC)

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Is the expression for solubility of Iron Phosphate and Calcium Suphate in the table in the "Dissolution with dissociation" incorrect?

In the "Dissolution with dissociation" section, "ionic compounds" subsection, there is an explanation of calculating solubility in terms of Ksp and a table of how this works for various compounds.

In this table, it is stated that the solubility expression for calcium sulphate (CaSO4) is stated to be (Ksp/16)^0.25 and the solubility expression for Iron Phosphate (FePO4) is stated to be (Ksp/729)^(1/6).

Since "p" and "q" are based on stoichiometric constants and not on charge, should the solubility expression not be (Ksp)^0.5 for both compounds?

158.194.9.137 (talk) 14:47, 2 November 2017 (UTC)

Electrical charges are implicit in the derivation as they determine the stoichiometry of the dissociation reaction. When a salt dissolves in a solvent electrical neutrality must always be maintained. This is the basis for the equilibrium expression

A_pB_q ⇌ p A^q+ + q B^p−

p * q⁺ - q * p^- =0 implies maintenance of overall charge neutrality. Petergans (talk) 10:26, 4 November 2017 (UTC)

Hello Petergans,

I apologise for imprecise communication. I was not disputing that the stochiometry of dissociation of salts is dependent on charge. What I was questioning is that since,

FePO₄ ⇌ Fe³⁺ + PO₄^3-;

if S=[FePO₄], then [Fe³⁺]=S and [PO₄^3-]=S,

thus the Ksp=[Fe³⁺][PO₄^3-]=S²,

therefore S=Ksp^1/2 and not (1/729)×Ksp^1/6. However, it is the latter expression that is given in the table.

Likewise for CaSO₄, the dissocation is: CaSO₄ ⇌ Ca²⁺ + SO₄^2-,

therefore Ksp=[Ca²⁺][SO₄^2-]=S²,

thus in this case, like in the previous case, shouldn't S=Ksp^1/2? Instead of (1/16)×Ksp^1/4 which is written in the table?

Once again, I am not disputing the basic chemistry. Rather I am questioning the expressions in the table, because they don't seem right for some of the compounds. 158.194.9.137 (talk) 12:49, 8 November 2017 (UTC)

You are right! Many thanks for the observation. I have revised section concerned. Petergans (talk) 15:12, 9 November 2017 (UTC)

Situations that require the use of activities

I think that some cases where activities are needed in calculations for the system solid salt-solvent should be mentioned by the article.--82.137.14.73 (talk) 21:05, 21 November 2017 (UTC)

Solubility

The temperature dependence that was given

$(1)\left({\frac {\partial \ln x_{i}}{\partial T}}\right)_{P}={\frac {\Delta H^{\ominus }}{RT^{2}}}$

is unsourced and conflicts with the definition given in Denbeigh, "The principles of chemical equilibrium", page 308

$(2){\frac {\partial \ln(S.P.)}{\partial T}}={\frac {H^{0}-h'}{RT^{2}}}$

where $H^{0}$ is the partial molar enthalpy of the electrolyte at infinite dilution and h' is the enthalpy per mole of the pure crystal.

Atkins, "Physical chemistry" p153 (8th edition) states that although solubility is not strictly a colligative property...

$(3)lnx_{B}={\frac {\Delta _{fus}H}{T}}\left(1/T_{f}-1/T\right)$

It is not clear that the two expressions (2) and/or (3) are equivalent to (1). A source citation will needed if expression (1) is to be reinstated. Petergans (talk) 11:42, 10 July 2019 (UTC)

I think the expression (1) is incomplete or has typos. The other two expressions should be inserted in article with their sources.--93.122.250.117 (talk) 15:55, 10 July 2019 (UTC)

A question appears in this context: Does the source Denbigh present only the case of electrolytes solubility equilibrium with solubility products?--37.251.222.165 (talk) 21:58, 10 July 2019 (UTC)

Section 10-10 in Denbeigh is entitled Phase equilibrium of an electrolyte. Solubility product. Indeed, the whole chapter is entitled Reaction equilibrium in solution, Electrolytes. The case of non-electrolytes is discussed in this article in section below, "Simple dissolution".

The concern with unsourced material in this instance is that one cannot check whether specific conditions or approximations apply to the equation originally in the article. It has now been revised and reinstated without citation. This is unsatisfactoryPetergans (talk) 11:29, 11 July 2019 (UTC)

Unsatisfactory of course for the moment. I'm thinking what to cite. The version I have is equivalent to Atkins version, but in differential form, not integrated. Perhaps there is also a differential expression with mole fraction solubility in Atkins, at some other page? Is it OK to cite Atkins for the unintegrated expression I have acces to? (a NON-ENG source)--109.166.137.150 (talk) 00:35, 12 July 2019 (UTC)

Another aspect concerns the separation between electrolytes and non-electrolytes re the dependence on temperature. Should we include also a separate tempdep in the Simple dissolution section to present the dependence?--109.166.137.150 (talk) 00:43, 12 July 2019 (UTC)

I have included the cited integrated form from Atkins.--109.166.128.144 (talk) 01:13, 13 July 2019 (UTC)

Mixed solvents systems

I notice that this article does not include info re the solubility equilibrium of substances in mixed solvents.--109.166.137.83 (talk) 23:36, 19 July 2020 (UTC)

K_sp isn't equal to [Ca]^3 (?)

In the section regarding the solubility product, it is stated that, since in a calcium hydroxide solution the number of hydroxide anions is double the amount of calcium cations, the solubility product K_sp = [Ca2+][OH-]^2 reduces to K_sp = [Ca2+]^3.

How is this possible if the concentration of OH-, as previously stated, is double the concentration of Ca2+? Shouldn't the solubility product equal [Ca2+]{2*[Ca2+]}^2, and thus 4[Ca2+]^3?

This seems to be reinforced by the immediately following table.

Is this correct? 93.43.184.56 (talk) 13:11, 17 November 2021 (UTC)

Yes. It follows from $\mathrm {K_{sp}=[Ca][OH]^{2}}$, since [OH] = 2 [Ca] Petergans (talk) 14:27, 17 November 2021 (UTC)