Mistake Master
Net ionic equations
In solution, a lot of the ions are just watching. A net ionic equation throws out those spectators and shows only what actually reacts — but only if you split the right species and cancel only the truly identical ones.
§1
Stripping down to what changes.
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A net ionic equation shows only the species that change during a reaction. You get there in three steps, starting from the balanced molecular equation.
First, write the complete ionic equation by dissociating the strong, soluble electrolytes into ions. Solids, gases, weak acids, and other molecular species stay together, undissociated.
Then cancel the spectator ions — the ones that appear identical and unchanged on both sides. What remains is the net ionic equation, showing the real chemistry (for example, the formation of a precipitate).
§2
The three-step sequence.
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Split the right species, cancel only the identical ones.
- Write the balanced molecular equation. Include states: (aq), (s), (l), (g).
- Dissociate strong electrolytes only. Split soluble ionic compounds and strong acids/bases into ions. Keep solids, gases, weak acids, and molecular species together.
- Identify spectator ions. Any ion that is identical and unchanged on both sides is a spectator.
- Cancel spectators to get the net ionic. Remove the spectators; only the species that actually change remain.
§3
The pieces you'll meet.
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Know what splits and what cancels.
§4
Worked example: silver nitrate plus sodium chloride.
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Molecular. AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq).
Complete ionic. Dissociate the soluble strong electrolytes: Ag⁺ + NO₃⁻ + Na⁺ + Cl⁻ → AgCl(s) + Na⁺ + NO₃⁻. The solid AgCl stays together — it is not soluble, so it does not split.
Spectators. Na⁺ and NO₃⁻ appear unchanged on both sides; they are spectators.
Net ionic. Cancel the spectators: Ag⁺(aq) + Cl⁻(aq) → AgCl(s). That is the real reaction — silver and chloride ions forming a precipitate.
§5
Mistakes that cost real points.
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"Split the solid product into ions too."
Only soluble strong electrolytes dissociate. A solid precipitate (like AgCl) is written together, not split into ions, because it is not dissolved. Splitting the solid destroys the whole point of the net ionic equation.
Fix. Keep solids (and gases and weak acids) together. Dissociate only the soluble strong electrolytes in solution.
"Weak acids should be split into ions like strong ones."
Weak acids barely dissociate, so they are written as intact molecules in ionic equations, not as separated ions. Only strong acids (and other strong electrolytes) are split. Treating a weak acid as fully dissociated is a common error.
Fix. Split strong electrolytes only. Write weak acids (and weak bases) as whole molecules.
"Any ions on both sides can be canceled."
Only ions that are identical and unchanged on both sides are spectators and can be canceled. Canceling ions that differ, or that are part of a formed solid, produces a wrong equation.
Fix. Cancel an ion only if the exact same ion appears unchanged on both sides; otherwise it participates.
§6
Skill Check.
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Ten scenarios. Pick the chips that match your answer, then check. A scenario marks complete the first time every part is right. Progress saves on this device.