# Various meanings of Ka, Kb etc

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 $K_\mathrm{a}$, $K_\mathrm{eq}$, ...?

• @MaxW All the temporary element names (systematic element names) were/are/will be three letters. Unu, Unb, Unt, Unq, Unp, Unh, ... Mar 1, 2017 at 9:05
• 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 1, 2017 at 12:48
• 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 1, 2017 at 12:49
• @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 1, 2017 at 13:11
• 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. Mar 15, 2017 at 10:34