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A little while back, I introduced the feature to mhchem to properly format $K$ constant variables, like $\ce{Ka}$ rendering as $K_\mathrm{a}$, $\ce{pKb}$ rendering as $\mathrm{p}K_\mathrm{b}$, etc. (besides $\ce{K_a}$ and $\ce{pK_b}$).

I was inspired by seeing quite some usage of Ka, pKb inside \ce, here at Chemisty.SE. I also checked if there were other meanings of these terms and found none.

But now, I am getting doubts how future-proof this is. What if the next new chemical element's name will have the 'Ka' abbreviation? What if some field will invent the 'Ka' 'nickname'?

Do you know any other meaning of Ka, Kb, Kw, Kf, Kc, Kp, Ka1, Ka2, Ka3, Kb1, Kb2, Kb3, Keq, Ksp other than $K$ constants? How likely is it that alternative meanings for these will emerge?

Or, to phrase it differently: How likely is it (or will it be) that somebody typing \ce{Ka}, \ce{Keq}, ... does intend other output than $K_\mathrm{a}$, $K_\mathrm{eq}$, ...?

mhchem
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  • Ha? These are just arbitrary symbols of mathematical, chemical constants, and have been used long before you were even born. Except $pK_a$ and $pK_b$, which are clearly defined symbols. – Karl Mar 01 '17 at 07:37
  • Ooops, some grammatical mixup in the last sentence. I rephrased it (and added one more). Does it make sense now? – mhchem Mar 01 '17 at 07:47
  • Much better. I don't understand how the system works, though. Is the list you give above complete? – Karl Mar 01 '17 at 08:01
  • There are a number of two-letter symbols in use. Deborah number $De$, Raleigh number $Ra$, Weissenberg number $We$, and quite a few more in other fields. https://de.wikipedia.org/wiki/Dimensionslose_Kennzahl The Knudsen number $Kn$ might collide with your system, perhaps. – Karl Mar 01 '17 at 08:06
  • I can't imagine an element name have 3 letters (Ksp Keq), having a number would be really really weird. Ka seems the only one in some danger. Hopefully the powers to be would realize the problem and choose something else. – MaxW Mar 01 '17 at 08:07
  • Do you have any statistics about who uses your "abbreviations"? It seems a bit strange to add the \ce tag to a simple mathematical constant. – Karl Mar 01 '17 at 08:16
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    @MaxW All the temporary element names (systematic element names) were/are/will be three letters. Unu, Unb, Unt, Unq, Unp, Unh, ... – mhchem Mar 01 '17 at 09:05
  • @Karl. It is a very, very low percentage. You can easily scan the list yourself. Therefore, it is not a big deal if I would remove support again. But also consider all the posts that were entered as Ka and got fixed by others because it did not render properly. – mhchem Mar 01 '17 at 09:22
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    I would rather not have $\ce{Ka}$ render $K_\mathrm{a}$. \ce{} is meant to typeset chemical expressions such as compounds or reactions. $K_\mathrm{a}$ is not a chemical expression, it is a physical/mathematical one. It makes practically zero sense to include these in the same command. Remember that a core principle of $\mathrm{\LaTeX}$ is to use semantic markup — having a chemical markup for a physical constant violates that rule. – Jan Mar 01 '17 at 12:48
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    I think that most of the uses of $\ce{Ka}$ on site were people thinking ‘Ah, when my last post using CO2 was corrected, they wrote $\ce{CO2}$. So now that I have Ka it should probably be $\ce{Ka}$. And in the next line $\ce{m=5g}$.’ Do you really want to account for every semantic misuse? – Jan Mar 01 '17 at 12:49
  • But since these two do not answer the question, they shall remain comments. – Jan Mar 01 '17 at 12:49
  • @Jan I understand your "not every misuse" argument. But could you explain why you think the acid dissociation constant is not a chemical expression? – mhchem Mar 01 '17 at 13:07
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    @mhchem Simply because it is used in physical (or physicochemical) equations. The same is true for pressure, partial pressure, mole fraction, amount of substance, volume and any other physical constant/variable that can be attributed to a single compound. – Jan Mar 01 '17 at 13:11
  • I endorse what Jan says. – Karl Mar 01 '17 at 23:21
  • Let's move over to Meta: About the scope of mhchem – mhchem Mar 02 '17 at 07:44
  • @Jan The acid dissociation constant is a mathematical object used in the course of describing a chemical phenomenon. It is not itself a chemical expression. – hBy2Py Mar 14 '17 at 17:10
  • @hBy2Py My point exactly, except I used mathematical expression** rather than object. – Jan Mar 15 '17 at 00:20
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    That's nitpicking. $K_\mathrm{a}$ is a symbol for a ... "thing" ... mostly used in chemistry. Wikipedia puts $K_\mathrm{a}$ in the chemistry category. Following your arguments, one could could state that the + in a chemical equation is not chemical, but a mathematical character describing a chemical phenomenon. Or one could say that oxidation states should not be part of \ce because they are a "dimensionless number of chemistry" just as $K_\mathrm{a}$ is. I am very open for arguments to remove $K_\mathrm{a}$ support from \ce, but please don't tell me $K_\mathrm{a}$ is not chemical. – mhchem Mar 15 '17 at 10:34

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