Net ionic equations show the chemical change that actually happens in a reaction in water. They remove ions that are present but do not participate, making the reaction easier to understand. This matters because many reactions in chemistry involve dissolved ionic compounds, acids, and bases.
Net ionic equations help students focus on precipitate formation, water formation, gas formation, or electron transfer.
Key Facts
- Molecular equation: AgNO3(aq) + NaCl(aq) -> AgCl(s) + NaNO3(aq)
- Complete ionic equation: Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) -> AgCl(s) + Na+(aq) + NO3-(aq)
- Net ionic equation: Ag+(aq) + Cl-(aq) -> AgCl(s)
- Spectator ions appear unchanged on both sides of the complete ionic equation.
- Strong acids, strong bases, and soluble ionic compounds are written as separated ions in complete ionic equations.
- For strong acid and strong base neutralization, the common net ionic equation is H+(aq) + OH-(aq) -> H2O(l).
Vocabulary
- Molecular equation
- A chemical equation that shows reactants and products as complete formulas rather than separated ions.
- Complete ionic equation
- A chemical equation that shows all soluble strong electrolytes as separate ions in aqueous solution.
- Net ionic equation
- A chemical equation that includes only the particles that directly take part in the chemical change.
- Spectator ion
- An ion that appears unchanged on both sides of a complete ionic equation and is not part of the net reaction.
- Precipitate
- An insoluble solid that forms when ions in aqueous solution combine.
Common Mistakes to Avoid
- Splitting solids, liquids, or gases into ions is wrong because only aqueous strong electrolytes are separated in complete ionic equations.
- Canceling ions that are not identical is wrong because spectator ions must have the same formula, charge, state, and amount on both sides.
- Forgetting to balance atoms and charge is wrong because a net ionic equation must conserve both mass and total electric charge.
- Writing weak acids as fully separated ions is wrong because weak acids mostly remain as molecules in solution and should usually be kept together.
Practice Questions
- 1 Write the molecular, complete ionic, and net ionic equations for mixing 0.10 M AgNO3(aq) and 0.10 M NaCl(aq).
- 2 When 25.0 mL of 0.200 M HCl reacts completely with 25.0 mL of 0.200 M NaOH, write the net ionic equation and calculate the moles of water formed.
- 3 Explain why K+(aq) and NO3-(aq) are often spectator ions in precipitation reactions, and describe how you would identify them in a complete ionic equation.