Polyprotic acids (polyacid acids or polyprotonic acids) are acids that have more than one ionizable hydrogen. These acids dissociate in more than one stage and each stage has its own equilibrium constant.
Polyprotic acids do not give up all the protons at once and with the same ease, but they do so in a staggered way, and each time with greater difficulty. The corresponding dissociation constants, decrease a lot (approximately a factor of 10) for each of the successive ionizations.
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