Talk:Molar concentration

Formula

I believe that the proper formula is $C={\frac {N*A}{V}}$ not $C={\frac {N/A}{V}}$ because it is moles per liter, and one mole is equal to number of molecules 8 Avogadro's number

Anyone else agree?

Wes5550 (talk) 20:44, 4 May 2008 (UTC)

The original formula is correct. By your definition (which is right) $C=M/V$. That makes it Moles per liter. What you are therefore trying to say is$M=N*A$. This isn't right. The amount of moles of a substance present is a fraction of Avagadro's Number... it is hence a division. Say you have 3.01 * 10^23 molecules of a substance X, using a division will derive the correct figure of 0.5M; I hope this makes sense. User: Mubinchoudhury —Preceding comment was added at 11:03, 6 May 2008 (UTC)

Wrong units

This part of the article is wrong:

mol/m³ = 10^-3 mol/dm³ = 10^-3 mol/L = 10^-3 M = 1 mM .

This implies, that

1 mol/m³ = 1 mM

Which is not correct —Preceding unsigned comment added by Hudejo (talk • contribs) 10:46, 16 March 2010 (UTC)

Why not? 1 mol/m³ (if anyone ever used that unit) is 1 mM. The article is only incorrect in implying that mol/dm³ is somehow not an SI unit. Physchim62 (talk) 11:06, 16 March 2010 (UTC)

Also, avogadro's number rounds to 6.022 X 10^23 not 6.023 X 10^23 —Preceding unsigned comment added by Elidurmer (talk • contribs) 01:47, 16 May 2010 (UTC)

Context

The introduction:

(a) is very heavy on jargon. For example, I have a basic knowledge of molarity and how it works (but I am NOT an expert) but haven't a clue what an atomic species is.

(b) Goes into specifics in a narrow topic area (thermodynamics.) About two-thirds of the introduction is about this topic. Thermodynamics might an excellent section in the body of this article, but is unnecessary in introducing what Molarity is.

Michaeloqu (talk) 03:38, 26 May 2010 (UTC)

Specialized aspect of its associated subject (aka "Reorganization")

Molarity is a basic concept, and it is used in many disciplines. This article could be improved by adding sections that cover a fair sampling of those disciplines and how the concept of molarity is relevant to that discipline.

There is a seed of this in the thermodynamics discussion in the introduction, and even better in the examples. IMHO it just needs more. Breaking it down by discipline helps establish context of what is, admittedly, a fairly abstract topic that most people do not use on a regular basis.

There also needs to be a section (at the top) that explains molarity in terms an educated layman would be able to understand. Think Chem 101, or possibly High School Chemistry.

Michaeloqu (talk) 03:38, 26 May 2010 (UTC)

Needs an expert

I do not have enough expertise in this are to write anything even close to the truth at the detail level. If I did, I would do so. I can re-arrange the article to reflect the the changes I am suggesting in the last two sections, but then someone else would have to come along behind me and flesh it out with the actual content.

NON SEQUITUR: I'm pretty new to editing, and I can't find guidance on signing my edits when I create or edit multiple sections on a talk page. Do I sign once at the bottom, or at the end of each section? Since it makes the most sense to me, I will sign each section right now. I would appreciate it if someone could let me know. Thank you.

Michaeloqu (talk) 03:38, 26 May 2010 (UTC)

Milliosmoles etc.

As a professor of biology who specifically teaches anatomy and physiology I can inform you that milliosmoles are definitely used in a clinical setting, thus, knowing mM is an important concept and shouldn't be taken out.

As for the jargon, it's hard not to use it. I would like to know what the main confusion is on the page and where or what people would like to see additional examples of. Also, why is it that the concentration page has a nice discussion of molarity and molality (see Concentration) that isn't utilized here? Or another question would be, why do we have a seperate page for molarity at all?

—Preceding unsigned comment added by Tjcheckley (talk • contribs) 05:16, 30 September 2010 (UTC)

excessive tagging helps no one

please do not clutter the article with quality tags, without discussing here why you think they're needed. -- 99.233.186.4 (talk) 23:56, 20 January 2011 (UTC)

molar density

I see several problems with the new section about "molar density":

• Only important things should appear at the beginning of the article. The relation to "molar density" is certainly not important for someone who wants to read about molar concentration.

• Molar density is not defined in wikipedia at all. "Density" is not the same as "molar density". Therefore, the link to density only creates confusion. Also, using $\rho$ for both the "density" and the "molar density" creates even more confusion.

• The equation, although formally correct, is of no practical use: Measuring and adding up the molar concentrations of all components (including the solvent) is not a useful way to determine the density of a solution. RolfSander (talk) 17:04, 14 April 2011 (UTC)

Remarks to the raised aspects:

• The sum of molar concentrations (total molar concentration) is a control/normalizing relation like that of the sum of mass/mole fractions which allows the finding of the molar concentration of a component when the others' are known. The sum in discussion can be called molar density. This name can be ignored.

• The relation can be used to determine the molar mass of the mixture knowing the density and the molar concentrations. An equivalent form is :$\rho =\sum _{i}c_{i}\cdot M_{i}$

• Total molar concentration appears in Maxwell-Stefan diffusion or in a version of Fick's law of diffusion which expresses the (molar) concentration gradient as a function of mole fraction gradient.--MagnInd (talk) 12:59, 15 April 2011 (UTC)

Although I'm still not very convinced that these conversions are useful, I have a suggestion how we can at least use a well-defined quantity instead of inventing new terms. What you call "total molar concentration" or "molar density" is actually the same as 1/(molar volume). Thus, in the section about mole fraction you could add that:

$x_{i}=c_{i}\cdot M/\rho =c_{i}\cdot V_{m}$

RolfSander (talk) 14:30, 15 April 2011 (UTC)

Sure, the reciprocal of molar volume of the mixture, this volume being the weighed sum of the partial molar volumes.--MagnInd (talk) 18:17, 15 April 2011 (UTC)

Molinity

Speaking of terms with questionable status, does the term ‘‘Molinity’’ (the quotient amount of solute/mass of solution) exist? I″ve encountered it (probably on former revisions of the Concentration page) once by browsing wp.--MagnInd (talk) 18:29, 15 April 2011 (UTC)

I've never heard the term ‘‘Molinity’’ while studying chemistry. A quick google search leads to only a few pages and nothing that looks very reliable. I don't see the need to include it in wikipedia. RolfSander (talk) 19:29, 15 April 2011 (UTC)

Additions to article

The following should be added for the completion of the article:

• Dependence on volume and relation to the thermal expansion of mixtures.
• Spatial variation (gradient) aspects, etc--MagnInd (talk) 09:34, 23 June 2011 (UTC)

Good idea to add these to wikipedia. However, I'm not sure if molar concentration is the right place for it:

• Dependence on volume applies to all concentrations (molar, mass, number) thus it might be better to place the new text into the generic concentration article.
• Solutions with gradients not only have different concentrations at different locations but also different molalities, molar fractions etc. Maybe add some text to the solution page? Currently, a solution is described there as a homogeneous mixture.--RolfSander (talk) 13:15, 23 June 2011 (UTC)

• Of course on all concentrations pages dependence on volume aspects should be inserted, as well as on the generic concentration article.

• The solution page should be adjusted. The homogenous mixture must be reffering to the existence of a single phase, not to spatial variation. The gradient of concentration, as well as of fractions and molality, appearing in Fick's laws, is essential to diffusion phenomena.--MagnInd (talk) 21:07, 26 June 2011 (UTC)

• I don't like to repeat almost identical information on different pages. It is quite impossible to keep them synchronized. I'd prefer to have the main description on the generic concentration article, and add just one sentence to the other pages like: "Note that the ... concentration depends on volume and thus on thermal expansion, as explained on the concentration page."

• I agree regarding the solution page -- RolfSander (talk) 08:23, 27 June 2011 (UTC)

Solution adjusted.--MagnInd (talk) 09:34, 30 June 2011 (UTC)

Of course the generic sentence about the dependence on volume should be inserted for start under section properties for start on all concentration pages involved. The full analysis should involve aspects/refer to conections to partial molar properties, excess and apparent molar properties and the two volume-concerning expressions (volume concentration and volume fraction). The generic analysis fits the concentration page and the specific pages should show specific small differences from case to case.--MagnInd (talk) 09:40, 17 July 2011 (UTC)

Reciprocal

One could ask what molar volume represents the reciprocal of molar concentration?--MagnInd (talk) 21:56, 20 March 2013 (UTC)

Due to appearance in the law of dilution the name dilution or dilution volume appears appropriate.--MagnInd (talk) 09:15, 24 August 2013 (UTC)

The article hides a peculiar historic fact?

Is it a fact that Molar (M) has been invented after 1980 from under the convention of the physics Gravity force, G, to the physics constant of gravity, g, also as pedagogical trick, in line with the ISO we see today?
It may be surprising to the readers to learn that M, the chemical Molar, is of recent invention...
Links: ISO - http://en.wikipedia.org/wiki/ISO and http://en.wikipedia.org/wiki/Gravity . 95.34.121.41 (talk) 14:28, 6 June 2013 (UTC)

I learned about Normality and Molarity of solutions when I was studying chemistry at school in the mid 1970s, so I think you (95.34.121.41?) must be making an unwarranted assumption of some kind. I think the answer to your initial question is, "No".Hedles (talk) 07:14, 20 June 2019 (UTC)

mol-% / mol%

I just came across the term mol-% or mol% a few days ago for the first time. Would this be a good page for a definition? c.f. https://www.researchgate.net/post/What_is_meant_by_mol

Hedles (talk) 08:12, 20 June 2019 (UTC)

No, not here. You can find mol-% there: Mole fraction --RolfSander (talk) 11:07, 22 June 2019 (UTC)

Great thanks, Rolf. Then ought there to be a redirect to it called "Mol-%" or is "mol-%" an incorrect usage for "mol%"?

Context is Polymer_electrolyte_membrane_electrolysis#Advantages_of_PEM_electrolysis. Should this correctly read

" . . . standard conditions 4 mol% H₂ in O₂ . . ." instead of

" . . . standard conditions 4 mol-% H₂ in O₂ . . ." as it currently does.

Googling "Mol-%" didn't find Mol%. So if "Mol-%" is equally correct usage, then I think that another redirect would help functionality. Contrariwise, if "mol-%" is incorrect/depreciated, then it ought to be changed to "mol%" in the Polymer_electrolyte_membrane_electrolysis article. (I have linked the occurrence of "Mol-%" in the paragraph to Mole fraction.) There also seems to be about the same amount of the usage "mol %" (e.g. https://www.researchgate.net/post/What_is_meant_by_mol), on the web - i.e not much. Is there a correct usage?

Incidentally, would you care to express an opinion on what is meant by "The safety limits for H₂ in O₂ are at standard conditions 4 mol-% H₂ in O₂."?

Does it mean, "At standard conditions, the safety limit, for the amount of hydrogen in oxygen, is (no more than) 4 mol-% of H₂."?

If so, would "4 mol-% H₂ in O₂" be a standard way of expressing this? It now seems to me to be the only way to interpret it, but - I think mostly because of having no commas, it took me a few re-reads to reach the conclusion that this is what it means, so I've been casting around for a better way to write it in order that it is less easy for others to mis-parse it. Hedles (talk) 18:16, 23 June 2019 (UTC)

"Equimolar" listed at Redirects for discussion

An editor has identified a potential problem with the redirect Equimolar and has thus listed it for discussion. This discussion will occur at Wikipedia:Redirects for discussion/Log/2022 March 2#Equimolar until a consensus is reached, and readers of this page are welcome to contribute to the discussion. 1234 kb of .rar files (is this dangerous?) 13:32, 2 March 2022 (UTC)

Physicality of 'Megamolar' (MM)?

The article clarifies the meaning of MM when viewed as a symbol for concentration. However, a 'megamolar' is a nonsense unit, because the maximum concentration that can be reached is in the tens of molars; beyond this point one is stretching the definition of a 'solution'. The solid phase of Osmium, for example, has a 'molarity' (dimensionally speaking) of order 10^2M. This clarification should therefore be removed unless a publication which specifically uses MM (perhaps by some really eccentric astronomer) can be found, because it causes unnecessary confusion. 2003:A:D48:9800:54B3:7EE9:25B4:E958 (talk) 10:54, 31 October 2023 (UTC)

Indeed, MM is not very useful. I've adjusted the text.--RolfSander (talk) 11:06, 31 October 2023 (UTC)