Construct and combine oxidation and reduction half-equations to balance redox reactions.

What this dot point is asking

You must construct balanced half-equations and combine them into a balanced full redox equation.

Why half-equations help

A redox reaction is electron transfer: one species is oxidised (loses electrons) and another is reduced (gains electrons). Splitting the reaction into two halves lets you track the electrons explicitly and balance even complicated reactions reliably.

Balancing a half-equation in acidic solution

Use this order for each half:

• Balance the atoms being oxidised or reduced.
• Balance oxygen by adding $\text{H}_2\text{O}$.
• Balance hydrogen by adding $\text{H}^+$.
• Balance charge by adding electrons $\text{e}^-$.

Electrons appear on the left of a reduction half-equation (gained) and on the right of an oxidation half-equation (lost).

Checking your answer

A correctly balanced redox equation has the same number of each atom on both sides and the same total charge on both sides. Always verify the charge balance; it is the step most often skipped.

In the exam, write each half-equation clearly, follow the atom-then-charge order, scale for equal electrons, cancel them on combining, and finish by checking both atom and charge balance.