Question

$H_3{PO}_4$ is triprotic. Prove.

Answer 1

Orthophosphoric acid contains three relaceable $H$ atoms and it reacts with alkali to form three series of salts. So it is named as triprotic.
$H_3{PO}_4+NaOH\to \underset{Sodiumdihydrogenphosphate}{Na{H}_2{PO}_4}+H_{2}O$
$H_3{PO}_4+2NaOH\to \underset{Disodiumhydrogenphosphate}{{Na}_{2}H{PO}_4}+2H_{2}O$
$H_3{PO}_4+2NaOH\to \underset{sodiumphosphate}{{Na}_3{PO}_4}+2{3H}_{2}O$