What is the word to describe the number of acidic hydrogens an acid has? I am currently thinking something like "proticity", but I am not sure The use case world be for a table of things like this:

Acid    | Proticity
CH₃COOH |  1
H₂SO₄   |  2
H₃BO₃   |  3

Or in a set of statements like this:

The volume of gas produced by reaction A was 4.6 L. The proticity of Acid B was 3. The tare mass of object C was 4.76 g. The density of substance D was 7.8 g/mL.

Is there a specific word used to refer to this quantity? What word should I use to refer to it?

  • 4
    $\begingroup$ I don't know if there is an accepted term, but if there is not one, let's use "proticity". I like it. $\endgroup$
    – Ben Norris
    Commented Sep 27, 2014 at 19:18

3 Answers 3


The term that I learned was (ironically) "basicity."

I'm not sure if that's the standard term, or even if there is a standard term, but this refers to how many bases you need to neutralize the acid completely.

EDIT: Thanks for the correction from LDC3: the "basicity" of an acid refers to how many bases you've already added to it. Thus, $\ce{NaH2PO4}$ would be "sodium phosphate, monobasic," $\ce{Na2HPO4}$ would be "sodium phosphate, dibasic," and so on.

Again, not sure if this is standard terminology.

  • 3
    $\begingroup$ If you go to a chemical site (like Sigma-Aldrich) the formula $\ce {NaH2PO4}$ is called phosphoric acid, monobasic and $\ce {Na2HPO4}$ is called phosphoric acid, dibasic because of the number of bases (2 NaOH) use to get the compound. $\endgroup$
    – LDC3
    Commented Sep 27, 2014 at 17:56
  • 1
    $\begingroup$ This is accepted terminology AFAIK. I've seen Wikipedia use it too consistently across articles, and I've seen chemical bottles use "sodium phosphate, monobasic" (or "dibasic") as you mentioned. $\endgroup$
    – Dissenter
    Commented Sep 27, 2014 at 18:07
  • $\begingroup$ @LDC3 You might be right. Unfortunately, Sigma Aldrich seems to be down for me right now. I will check and update the answer when it comes online, but curiously, Wikipedia seems to say the opposite. Maybe an editor got confused one day? en.wikipedia.org/wiki/Dibasic $\endgroup$
    – chipbuster
    Commented Sep 27, 2014 at 18:56
  • $\begingroup$ Checked the sigma and other sources, and I stand corrected. $\endgroup$
    – chipbuster
    Commented Sep 29, 2014 at 21:27

Proticity does sound nice, but it is a bad choice since the term has already been introduced by Peter D. Mitchell (1978 Nobel Prize in Chemistry) in a completely different context.

In his Nobel Lecture, Peter D. Mitchell explains:

I use the word proticity for the force and flow of the proton current by analogy with the word electricity, which describes the force and flow of an electron current.

  • $\begingroup$ Very interesting. What would you propose, then? $\endgroup$
    – ringo
    Commented Dec 2, 2016 at 9:04
  • 1
    $\begingroup$ @ringo Honestly, I don't know a good noun in English (or German). In both languages, I have always used inelegant constructions (multiprotonic acids / mehrprotonige Säuren) instead. $\endgroup$ Commented Dec 2, 2016 at 9:12
  • 2
    $\begingroup$ I think the context is different enough that we can cope with the identical word meaning different things. There are other examples, where it’s much worse. $\endgroup$
    – Jan
    Commented Dec 3, 2016 at 0:50

Monoprotic, Diprotic, Trioprotic, tetraprotic, pentaprotic, hexaprotic, septaprotic, octaprotic....


I then suggest "equivalents factor," which is directly related to the concept of normality:

"Normality isn't the same like Molarity, but you can say N = M * equivalents. 1 M HCl = 1 N HCl, but 1 M H2SO4 = 2 N H2SO4..." -source

  • $\begingroup$ I already know those words; what I am looking for is a word for the number itself. $\endgroup$ Commented Sep 29, 2014 at 0:39

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