What are diprotic and triprotic acids? Explain with differentiation.
Polyprotic acids are acids that have more than one ionizable proton per molecule. These are also known as polybasic acids.
$1$. Diprotic acid: An acid that has two ionizable protons per molecule. It ionizes in two steps:
$(i)$ $H_2X + H_2O \rightleftharpoons H_3O^{+} + HX^{-}, K_{a(1)}$
$(ii)$ $HX^{-} + H_2O \rightleftharpoons H_3O^{+} + X^{2-}, K_{a(2)}$
Here,$K_{a(1)} > K_{a(2)}$. Examples: $H_2SO_4$,$H_2CO_3$,$H_2C_2O_4$.
$2$. Triprotic acid: An acid that has three ionizable protons per molecule. It ionizes in three steps:
$(i)$ $H_3A + H_2O \rightleftharpoons H_3O^{+} + H_2A^{-}, K_{a(1)}$
$(ii)$ $H_2A^{-} + H_2O \rightleftharpoons H_3O^{+} + HA^{2-}, K_{a(2)}$
$(iii)$ $HA^{2-} + H_2O \rightleftharpoons H_3O^{+} + A^{3-}, K_{a(3)}$
Here,$K_{a(1)} > K_{a(2)} > K_{a(3)}$. Example: $H_3PO_4$.
$1$. Diprotic acid: An acid that has two ionizable protons per molecule. It ionizes in two steps:
$(i)$ $H_2X + H_2O \rightleftharpoons H_3O^{+} + HX^{-}, K_{a(1)}$
$(ii)$ $HX^{-} + H_2O \rightleftharpoons H_3O^{+} + X^{2-}, K_{a(2)}$
Here,$K_{a(1)} > K_{a(2)}$. Examples: $H_2SO_4$,$H_2CO_3$,$H_2C_2O_4$.
$2$. Triprotic acid: An acid that has three ionizable protons per molecule. It ionizes in three steps:
$(i)$ $H_3A + H_2O \rightleftharpoons H_3O^{+} + H_2A^{-}, K_{a(1)}$
$(ii)$ $H_2A^{-} + H_2O \rightleftharpoons H_3O^{+} + HA^{2-}, K_{a(2)}$
$(iii)$ $HA^{2-} + H_2O \rightleftharpoons H_3O^{+} + A^{3-}, K_{a(3)}$
Here,$K_{a(1)} > K_{a(2)} > K_{a(3)}$. Example: $H_3PO_4$.
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Similar Questions
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Which species behave as Bronsted-Lowry acids?
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Which species behave as Bronsted-Lowry acids?
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