Click below to see the other techniques for balancing redox equations.
Balancing Redox Equations for Reactions in Acidic Conditions Using the Half-reaction Method
Redox reactions are commonly run in acidic solution, in which case the reaction equations often include H2O(l) and H+(aq). This page will show you how to write balanced equations for such reactions even when you do not know whether the H2O(l) and H+(aq) are reactants or products. For example, you may know that dichromate ions, Cr2O72-, react with nitrous acid molecules, HNO2, in acidic conditions to form chromium ions, Cr3+, and nitrate ions, NO3-. Because the reaction requires acidic conditions, you assume that H2O(l) and H+(aq) participate in some way, but you do not know whether they are reactants or products, and you do not know the coefficients for the reactants and products. An unbalanced equation for this reaction might be written
Cr2O72-(aq) + HNO2(aq) --> Cr3+(aq) + NO3-(aq) (acidic)
In order to balance equations of this type, we need a special technique called the half-reaction method or the ion-electron method.