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Home  >>  JEEMAIN and AIPMT  >>  Chemistry  >>  Equilibrium
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$pK_{a1}, pK_{a2}$ and $pK_{a3}$ of $H_3PO_4$ are respectively x, y and z. $pH$ of 0.1 M $Na_2HPO_4$ solution is

(a) 1

(b) $\frac{1}{2} (x+y)$

(c) $\frac{1}{2} (y+z)$

(d) $\frac{1}{2} (x+y+z)$

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1 Answer

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Answer: $\frac{1}{2} (y + z)$
$HPO^{2-}_4$ is amphiprotic
$HPO^{2-}_4 + H_2O \rightleftharpoons PO^{3-}_4 + H_3O^+$
$HPO^{2-}_4 + H_2O \rightleftharpoons H_2PO^-_4 + OH^-$
$\therefore pH $ of 0.1 M $Na_2HPO_4= \frac{pK_{a2} + pK_{a3}}{2} = \frac{1}{2} (y + z)$


answered Nov 29, 2013 by mosymeow_1

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