Balance the equation in acidic and basic solution.

Question

Balance the following equation in a) acidic solution b) basic solution.

MnO2 + H3AsO3 --> Mn 2+ + H3AsO4

Answer 1

MnO₂ + H₃AsO₃ --> Mn²⁺ + H₃AsO₄

Using the half reaction method:

MnO₂ ==> Mn²⁺

MnO₂ ==> Mn²⁺ + 2H₂O ... to balance oxygens

MnO₂ + 4H⁺ ==> Mn²⁺ + 2H₂O ... to balance hydrogens (in acid)

MnO₂ + 4H⁺ + 2e- ==> Mn²⁺ + 2H₂O ... to balance charge and this is the balanced half reaction

AsO₃^3- ===> AsO₄^3-

AsO₃^3- + H₂O ==> AsO₄^3- ... to balance oxygens

AsO₃^3- + H₂O ==> AsO₄^3- + 2H⁺ ... to balance hydrogens (in acid)

AsO₃^3- + H₂O ==> AsO₄^3- + 2H⁺ + 2e- ... to balance charge and this is the balanced half reaction

Adding the two half reactions, we get ...

MnO₂ + 2H⁺ + AsO₃^3- = ==> Mn²⁺ + H₂O + AsO₄^3- ... balanced for mass and charge

To balance in basic solution, do the same thing but when ever you add H+ to balance the hydrogens, also add the same number of OH- to both sides. At the end, combine H+ and OH- on both sides to make H2O and cancel common items on both sides to end up with the balanced equation.