Balance O with H2O and H with H+, then add OH- to convert to basic solution.
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Redox equations in basic solution are balanced first as if the solution were acidic, using H2O and H+. Hydroxide ions are then added to both sides in an amount equal to the H+ present, so that each H+ combines with an OH- to form water. Water molecules appearing on both sides are cancelled, leaving a final equation that contains OH- rather than H+. The result can be checked by confirming that atoms and charge balance on both sides. This procedure is needed for reactions in alkaline industrial and environmental systems.
Key ideas: In acid, use H2O and H+. In base, first balance as if acidic, then add OH- to both sides equal to the number of H+, combine H+ and OH- into water, and cancel duplicate water. Final answers in base contain OH- and no H+. Example: MnO4- + 2H2O + 3e- giving MnO2 + 4OH-.
Common mistakes and connections: Mistakes: leaving both H+ and OH- in the final equation, adding OH- to only one side, and using acid products in base solutions (Mn2+ forms in acid, MnO2 in neutral or basic). Permanganate gives a different reduced product depending on pH: Mn2+ (acid), MnO2 (neutral), MnO4 2- (strongly basic).
Permanganate takes up five electrons in acid (to Mn2+), three in neutral or basic solution (to MnO2), and one in strong base, changing the balanced equation. The interactive lesson shows this as a live animation or chart.
The balanced basic half-reaction for permanganate reduction to manganese dioxide is MnO4- + 2H2O + 3e- -> MnO2 + 4OH-.
Balance O with H2O and H with H+, then add OH- to convert to basic solution.
Balancing in Acidic and Basic Medium is a intermediate topic in Acids, Bases & Electrochemistry. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Acids, Bases & Electrochemistry first: Reducing Agent, Disproportionation, Balancing Redox: Half-Reaction Method.
The next topics in Acids, Bases & Electrochemistry are Electrochemical Cell and Galvanic Cell.
Yes. The interactive lesson includes a self-check question on Balancing in Acidic and Basic Medium, and the Acids, Bases & Electrochemistry quiz draws on every topic in this area.
Balancing in Acidic and Basic Medium is topic 43 of 105 in Acids, Bases & Electrochemistry.