BCECE Medical BCECE Medical Solved Papers-2014

Three reactions involving \[{{H}_{2}}PO_{4}^{-}\] are given below

I. \[{{H}_{3}}P{{O}_{4}}+{{H}_{2}}O\xrightarrow{{}}{{H}_{3}}{{O}^{+}}+{{H}_{2}}PO_{4}^{-}\]

II. \[{{H}_{3}}PO_{4}^{-}+{{H}_{2}}O\xrightarrow{{}}HPO_{4}^{2-}+{{H}_{3}}{{O}^{+}}\]

III. \[{{H}_{3}}PO_{4}^{-}+O{{H}^{-}}\xrightarrow{{}}{{H}_{3}}P{{O}_{4}}+{{O}^{2-}}\]

In which of the above does \[{{H}_{2}}PO_{4}^{-}\] act as an acid?

A) II only

B) I and II

C) III only

D) I only

Correct Answer: A

Solution :

Only in reaction (II) \[{{H}_{2}}PO_{4}^{-}\], gives \[{{H}^{+}}\] to \[{{H}_{2}}O\], thus behaves as an acid.