Redox Half-Reaction Balancer
Enter the two redox couples (the species that changes, before → after) and the medium. The tool balances each half-reaction with water, H⁺ or OH⁻ and electrons, then scales and combines them into a full balanced equation.
How to use this tool
Balance a redox reaction without doing the electron bookkeeping by hand. You give the two species that change, each as "before → after", and pick whether the reaction runs in acid or base; the tool returns the fully balanced equation.
What to enter
- Half-reaction 1: the first couple, reactant on the left, product on the right (e.g. MnO4- → Mn2+).
- Half-reaction 2: the second couple the same way (e.g. Fe2+ → Fe3+). Write charges as a trailing sign: Fe3+, Cr2O7^2-, MnO4-.
- Medium: acidic balances with H⁺, basic with OH⁻. Match this to your actual conditions; it changes the answer.
- Example chips: tap a preset pair to load a worked couple instantly.
Reading the result
The headline is the full balanced equation. Below it, each half-reaction is shown with the factor it was scaled by (so the electrons cancel) and the total electrons transferred. The tool infers which couple is oxidised and which is reduced from the charge balance.
Worked example
Permanganate oxidising iron in acid (MnO4- → Mn2+, Fe2+ → Fe3+) balances to MnO₄⁻ + 5 Fe²⁺ + 8 H⁺ → Mn²⁺ + 5 Fe³⁺ + 4 H₂O, with 5 electrons transferred.
Couples
Balanced
The tool reads which couple is oxidised (loses electrons) and which is reduced from the charge balance, then scales each half-reaction so the electrons cancel exactly. Medium matters: the same couples balance with H⁺ in acid and OH⁻ in base, giving different equations, match it to your real conditions.
Methodology
Each half-reaction is balanced by the ion-electron method: balance the principal element, add H₂O to balance oxygen, add H⁺ to balance hydrogen, then add electrons to balance charge. In basic medium an equal number of OH⁻ is added to both sides to neutralise the H⁺, and excess water is cancelled.
The half-reaction with electrons on the right is the oxidation; the one with electrons on the left is the reduction. Both are scaled to the least common multiple of their electron counts so the electrons cancel, then the two are summed and common H₂O / H⁺ / OH⁻ are reduced.
Known limits
- Each couple must share exactly one redox element (besides O and H) between reactant and product.
- One level of parentheses is parsed; charges are trailing only. Bracket/complex notation isn't supported.
- The tool does not look up which couple oxidises which: it infers oxidation vs reduction from the balanced charge.