Why do different $\ce{H}$ atoms in a polyprotic acid have different values of $\pu{K_a}$?
All $\ce{H}$ atoms (which can show acidic nature) have similar properties within the molecule. It does not matter which one reacts. For example, in $\ce{H3PO4}$, all the $\ce{H}$ atoms can be dissociated from the molecule to act as acids. All of them are attached to an $\ce{O}$ atom, which is attached to the central $\ce{P}$ atom. If all the properties are same, then why is $\pu{K_a}$ different?
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