Question

Which of the following is not a conjugate acid-base pair?

• A. $HPO _{3}^{2-},\, PO _{3}^{3-}$
• B. $H _{2} PO _{4}^{-},\, HPO _{4}^{2-}$
• C. $H _{2} PO _{4}^{-},\, H _{3} PO _{4}$
• D. $H _{2} PO _{4}^{-},\, PO _{3}^{3-}$

Answer 1

Answer: (D)

Acid $_{1}+$ Base $_{2} \rightleftharpoons$ Acid $_{2}+$ Base $_{1}$
$HPO _{3}^{2-}+ H _{2} O \rightleftharpoons H _{3} O ^{+}+ PO _{3}^{3-}$
$H _{2} PO _{4}^{-}+ H _{2} O \rightleftharpoons H _{3} O ^{+}+ HPO _{4}^{2-}$
$H _{3} PO _{4}+ H _{2} O \rightleftharpoons H _{3} O ^{+}+ H _{2} PO _{4}^{2-}$