Talk:Ionic strength

Units

Does ionic strength have the units of molarity? ike9898 17:21, 19 April 2006 (UTC)

Yes. − Twas Now ( talk • contribs • e-mail ) 15:50, 26 February 2007 (UTC)

NO - Reference Atkins-Depaula 8th edition. Ionic strength is a dimensionless quantity. The forumulas on this page do not accuractely reflect this fact, because they neglects (b/b0). —Preceding unsigned comment added by 150.243.36.41 (talk) 22:18, 13 December 2007 (UTC)

Above comment by me, Pckilgore (talk) 22:21, 13 December 2007 (UTC)

YES, dimensions of (moles of) ions per unit volume - http://www.ebyte.it/library/educards/sidimensions/SiDimensionsByCategory.html

I feel like this page needs units on the calculation of ionic strength, as units are important in the scientific field and would make it easier for students to understand the calculations--can that be added? -Karen McKelvie — Preceding unsigned comment added by 71.13.222.111 (talk) 18:00, 27 November 2012 (UTC)

The example in the article does show that if the concentrations are in mol/L (or mol-dm^-3), then ionic strength is also in mol/L. The problem is that not everyone uses mol/L. As the section on Non-ideal solutions says, some authors replace concentration in the definition of ionic strength by molality (mol/kg) so that the ionic strength is also in mol/kg. The IUPAC Gold Book mentions both choices. And still others (such as Atkins and de Paula, Physical Chemistry, 8th ed., p.164, cited above) divide the molality b by b° = 1 mol/kg to obtain a dimensionsless molality and therefore a dimensionless ionic strength (a pure number). All of these choices can be made compatible with the Debye-Huckel equation if the units of the constant A in that equation are changed appropriately.

Is this all worth explaining in detail? Dirac66 (talk) 00:09, 29 November 2012 (UTC)

Ionic strength should be considered dimensionless because molality (i.e. kg substance/kg water) should be used to determine ion concentration. If molality is used then the SI units of kg cancel each other out leaving ionic strength as dimensionless. Molality is a more suitable measure of concentration since it reduces complications that arise from the changing volume of the solvent (i.e. water) as temperature changes. BluesLewis (talk) 14:07, 30 August 2013 (UTC)

Um, molality is mol substance/kg water, so it is not dimensionless. Dirac66 (talk) 17:05, 2 September 2013 (UTC)

Ionic Replacement

I believe this should be split off into a seperate article, as it is not really about ionic strength. While the resulting article will refer to this page certainly, it is more of an experimental technique that deserves its own page, much in the way of Standard_addition Pckilgore (talk) 17:19, 15 December 2007 (UTC)

You are absolutely right. This section is irrelevant and I have deleted it. Petergans (talk) 09:47, 14 July 2008 (UTC)

Measuring ionic strength

Is there a direct way to measure ionic strength, whether with an instrument, some kind of titration, a fluorimetric probe, etc?

-- Tom Anderson 2008-01-16 2055 +0000 —Preceding unsigned comment added by 128.40.81.141 (talk) 20:55, 16 January 2008 (UTC)

organic substances

The above definitions involve two assumptions: (not mentioning it) 1) water solutions 2) complete (total) dissociation.

Organic compounds might dissolve in water, and might have more carboxylic groups. In principle the concentration should be different from the dissociated ions and more ionization steps are possible. E.g. ortho dibenzoic acid dissociates C₆H₄(COO^-)₂ + 2H⁺.

I have never seen ionic strength defined for organic compounds, but it would be logical: the sum of molal concentration of ions multiplied by their Z number and multiplied by the dissociation degree. —Preceding unsigned comment added by Karesz, Charlie (talk • contribs) 08:35, 10 September 2008 (UTC)

Equivalent expressions

The presence of the square of the charge number in the expression of ionic strength can be equivalently expressed by considering the absolute value of the charge number or the root square from the square of the charge number.--MagnInd (talk) 08:17, 5 October 2013 (UTC)

Ionic strength fraction

There seems to be a derived concept from ionic strength, namely ionic strength fraction which describes binary mixed electrolytes. Some details are useful to be included.--5.15.59.0 (talk) 10:55, 20 January 2016 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Ionic strength/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

=== Strengths === Examples, discussion of relevance to debye-huckle Pckilgore (talk) 17:11, 15 December 2007 (UTC) === Weaknesses === Weak definition it terms of current physical chemistry. Ionic strength should not have units.Pckilgore (talk) 17:11, 15 December 2007 (UTC)

Last edited at 17:55, 15 December 2007 (UTC). Substituted at 19:04, 29 April 2016 (UTC)

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Recent change in Molal (mol/kg): It doesn't have to be water ?

@Christian75: about your recent modification of Molal (mol/kg):

https://en.wikipedia.org/w/index.php?title=Ionic_strength&type=revision&diff=960168316&oldid=933081419

15:35, 1 June 2020 Christian75 talk contribs 7,422 bytes -6 Remove "water" in molal (mol/kg water). It doesn't have to be water

Just a request for clarification concerning your recent edit. What do you exactly mean? Is it water or another solvent (e.g., DMF, DMSO, liquid ammonia, (an ionic liquid or a molten salt, but then, I strongly doubt in such a case because of the very high electrolytic background ???), a mixture water/alcohol to modify the water dielectric constant and to decrease the solubility of some salts, or any organic solvent capable of dissociating an ionic substance...).

Or, is it the mass of the whole solution and not the mass of water considered here as the solvent of reference:

solution mass = solvent mass + solutes mass

solution mass = water mass + solutes mass

I was also puzzled by the term water considered as the solvent.

I am inclined to consider that it is the mass of the solution. Then, why not to clearly mention: mass of the solution, the aim being to get rid of volume changes due to the contraction or the expansion of the solution after mixing or dilution.

Remember also that the concept of ionic strength was initially defined for aqueous solutions where it is used in most of the cases. Maybe does it exist some relatively exotic research fields, where it is not water but another solvent. Then, we need to take care not to give an excessive place to something relatively rare.

Indeed, we need to avoid to puzzle the reader with a non-necessary big theoretical generalization which in fact is very rarely applicable and only deals with a very narrow research field poorly known.

I would suggest to stick to the simple case of ordinary aqueous solutions. However, if you are familiar with a rare application of the ionic strength concept to non-aqueous solvents, I propose that you create a new section dedicated to this special application with some relevant references to illustrate the ideas that you have in mind. Such as specialized section should have an appropriate size proportionate to the rest of the content of the page to avoid to cannibalize it, because the concept of ionic strength mainly deals with aqueous solutions.

What is your opinion and thanks to adapt the main page accordingly if considered relevant. Best regards, Shinkolobwe (talk) 15:58, 1 June 2020 (UTC)

@Shinkolobwe: I removed water because the lead talks about solutions (and not water). IUPACs definition (and out article) of molal i "Amount of entities of a solute divided by the mass of the solvent."(IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book")). Therefore, I added "solvent" in my last edit to clarify what molal means. The reference from "Journal of Chemical Education" talks about (a little) about solvents and polarity. Christian75 (talk) 16:50, 1 June 2020 (UTC)

@Christian75: Thank you for your quick answer and for this well sourced explanation. For more clarity, I also just added the term "L solution" to the definition of molarity: molar (mol/L solution). So, it is also clearer from this side. Shinkolobwe (talk) 17:41, 1 June 2020 (UTC)