question_answer 9)

Permanganate ion reacts with bromide ion in basic medium to give manganese dioxide and bromate ion. Write the balanced ionic equation for the reaction.

Answer:

Skeletal equation is \[\overset{+7}{\mathop{MnO_{4}^{-}}}\,+\overset{-1}{\mathop{Br}}\,\to \overset{+4}{\mathop{Mn{{O}_{2}}}}\,+\overset{+5}{\mathop{BrO_{3}^{-}}}\,\] Perusal of oxidation number confirms that \[MnO_{4}^{-}\] is oxidant while \[B{{r}^{-}}\] ion is reductant. The two half equations can be balanced as: \[[MnO_{4}^{-}+4{{H}^{+}}+3{{e}^{-}}\to Mn{{O}_{2}}+2{{H}_{2}}O]2\,\,\,\,\,\,\,\,\,\,\,......(i)\]\[B{{r}^{-}}+3{{H}_{2}}O\to BrO_{3}^{-}+6{{H}^{+}}+6{{e}^{-}}\,\,\,\,\,\,\,\,\,\,\,.......(ii)\] \[\frac{On\text{ }addition}{\frac{2MnO_{4}^{-}(aq)+B{{r}^{-}}+2{{H}^{+}}\to 2Mn{{O}_{2}}+BrO_{3}^{-}+{{H}_{2}}O}{{}}}\] On adding two \[O{{H}^{-}}\] ions on both sides we get the balanced equation in basic medium: \[2MnO_{4}^{-}(aq)+B{{r}^{-}}(aq)+\underbrace{2{{H}^{+}}(aq)+2O{{H}^{-}}(aq)}_{{}}\to \] \[2Mn{{O}_{2}}+BrO_{3}^{-}+2O{{H}^{-}}+{{H}_{2}}O\] \[2MnO_{4}^{-}(aq)+B{{r}^{-}}(aq)+{{H}_{2}}O\to \] \[2Mn{{O}_{2}}+BrO_{3}^{-}(aq)+2O{{H}^{-}}(aq)\]