Interactive redox balancing: iron and oxygen half-equations built step by step in acidic and basic solution, with electrons lost always equal to electrons gained

You never balance the whole equation — you split it into halves

A redox equation hides two jobs: one species loses electrons (oxidation) while another gains them (reduction). You write and balance each half on its own, then scale them so the electrons lost equal the electrons gained, and add. Here the example is rusting steel: iron gives up electrons at a paint chip and oxygen takes them at a wet patch nearby.

Electron transfer
Balanced
Move electrons from iron to oxygen through the steel and watch: every electron one side loses, the other side gains.
4 e⁻ lost = 4 e⁻ gained
Electron flow
Zero flow Balanced Twice over
Oxidation e⁻ lost
4
Reduction e⁻ gained
4
Build the equation
Step 1 of 6

    In acidic solution, balance each half in order: atoms other than O and H first, then oxygen by adding H₂O, then hydrogen by adding H⁺, then charge by adding electrons to the more positive side. Next multiply the halves so the electrons lost equal the electrons gained, add them, and cancel anything that appears on both sides. Finish with a check: every atom and the total charge must match on each side.

    Know This
    Redox balancing succeeds when you split the overall equation into oxidation and reduction half-equations, balance atoms (non-H/O first, then O with H₂O, then H with H⁺; extension: in basic solution, add OH⁻ to both sides to turn that H⁺ into water), balance charge by adding electrons, then multiply so electrons cancel when you add them together.