• What is the general name for acids that can only lose one hydrogen ion? (i.e. $\ce{HCl}$)
  • What is the general name for acids that can lose $n$ hydrogen ions? (i.e. $\ce{H_3PO_4}$, which can lose 3)

The answers to these questions are probably mentioned a million times on the internet, but I could not find them.


An acid that can donate one hydrogen ion is called monoprotic (i.e., $\ce{HCl}$). An acid that can donate two is called diprotic (i.e., $\ce{H_2SO_4}$). An acid that can donate 3 is called triprotic ($\ce{H_3PO_4}$). I don't know of any which can donate four.

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    $\begingroup$ An acid that can donate $n$ protons is called polyprotic, assuming $n > 1$. $\endgroup$ – Eric Brown Jun 3 '13 at 19:33
  • $\begingroup$ @EricBrown And assuming $n \in \mathbb{N}$. ;-) $\endgroup$ – Tim Vermeulen Jun 3 '13 at 20:07
  • $\begingroup$ @timjver tough crowd! :-) $\endgroup$ – Eric Brown Jun 3 '13 at 20:13
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    $\begingroup$ Just a side note: most polyprotic acids with more than three acidic hydrogens are organic, I believe, the first example that comes to mind being EDTA. There's only one inorganic tetraprotic acid I can think of off the top of my head, and that's pyrophosphoric acid. $\endgroup$ – Greg E. Jun 3 '13 at 20:16
  • $\begingroup$ Oh yes, I forgot about organic acids! If you make the chain long and branched enough you can squeeze just about as many carboxylic acids in as you want. $\endgroup$ – Zen Jun 3 '13 at 20:21

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