Given a complete ionic equation, click the spectator ions to cancel them out and reveal the net ionic equation.
Writing a net ionic equation — stripping away everything that doesn't actually participate in a reaction — reveals the true chemistry happening in solution, and this skill is tested throughout AP Chemistry Unit 4 (reaction types) and Unit 8 (acid-base chemistry).
The process starts with a complete molecular equation, which is then rewritten as a complete ionic equation by dissociating every soluble strong electrolyte into its constituent ions — using solubility rules to correctly identify which compounds actually dissociate (soluble ionic compounds and strong acids/bases) versus which remain as intact formula units (insoluble precipitates, weak acids/bases, water, and molecular gases).
Spectator ions are ions that appear identically on both the reactant and product side of the complete ionic equation, meaning they don't actually undergo any chemical change — they're simply present in solution as bystanders. Canceling spectator ions from both sides leaves the net ionic equation: the species that actually react.
Precipitation reactions are the clearest illustration: mixing AgNO3 and NaCl solutions, the complete ionic equation shows Ag+, NO3-, Na+, and Cl- ions on the reactant side, but Na+ and NO3- remain unchanged as spectators — the net ionic equation is simply Ag+(aq) + Cl-(aq) → AgCl(s), correctly showing that silver and chloride ions are what actually combine to form the solid precipitate, regardless of which soluble silver and chloride salts were originally used.
Acid-base neutralization between any strong acid and strong base reduces to the same net ionic equation every time: H+(aq) + OH-(aq) → H2O(l) — a powerful generalization showing that the "identity" of the acid and base (HCl vs HNO3, NaOH vs KOH) is chemically irrelevant to the net reaction, since those counterions are always spectators in a strong acid-strong base reaction. Gas-forming reactions, like a carbonate reacting with acid to release CO2, follow the same spectator-ion-removal logic.
This builder shows the complete ionic equation and lets you click spectator ions to cancel them, revealing the net ionic equation step by step across precipitation, acid-base, and gas-forming reaction types.