Question

For the following half cell reactions, $ E{}^\circ $ values are also given $ M{{n}^{2+}}+2{{H}_{2}}O\xrightarrow[{}]{{}}Mn{{O}_{2}}+4{{H}^{+}}+2{{e}^{-}}; $ $ E{}^\circ =-1.23V $ $ MnO_{4}^{-}+4{{H}^{+}}+3{{e}^{-}}\xrightarrow[{}]{{}}Mn{{O}_{2}}+2{{H}_{2}}O; $ $ E{}^\circ =+1.70V $ Select correct statements

• A. $ M{{n}^{2+}} $ reacts with $ MnO_{4}^{-} $ in acid solution to form $ Mn{{O}_{2}} $
• B. $ Mn{{(Mn{{O}_{4}})}_{2}} $ is stable in acid solution
• C. $ Mn{{O}_{2}} $ disproporttbnates to $ M{{n}^{2+}} $ and $ MnO_{4}^{-} $ in acid solution
• D. None of the above

Answer 1

Answer: (A)

$ 2MnO_{4}^{-}+3M{{n}^{2+}}+2{{H}_{2}}O\xrightarrow[{}]{{}}5Mn{{O}_{2}}+4{{H}^{+}}; $
$ E{}^\circ =0.47\,V $
Thus, cell reaction in which
$ M{{n}^{2+}} $ on reaction with $ MnO_{4}^{-} $ forms $ Mn{{O}_{2}} $ in acidic medium.