Lesson 2: 4.2 Net Ionic Equations

Why are some ions written explicitly as participating in a chemical reaction while others are ignored entirely?
How do we translate a full molecular equation into a net ionic equation for a precipitation reaction?

Net Ionic Equation
Complete Ionic Equation
Spectator Ion
Aqueous
Soluble
Insoluble
Dissociation

Learning Objective 4.2.A; Suggested Skill 5.B (Mathematical Routines/Balancing)

Students must master the distinction between molecular equations, complete ionic equations, and net ionic equations. They must identify and cancel out spectator ions (ions that remain dissolved and unchanged on both sides of the equation). This requires a firm grasp of solubility rules (specifically: all sodium, potassium, ammonium, and nitrate salts are completely soluble).

Support: Have students write out the complete ionic equation on a dry-erase board and physically draw a single bright red line through any ion that appears identical on both sides before copying down the remaining pieces.
Extension: Present a net ionic equation for a neutralization reaction between a weak acid and a strong base (e.g., HF(aq) + OH^-(aq) --> F^-(aq) + H2O(l)) and challenge students to explain why the weak acid cannot be split apart into separate ions on the reactant side.

Sample Problem: A student mixes an aqueous solution of barium chloride, BaCl2(aq), with an aqueous solution of sodium sulfate, Na2SO4(aq). A white precipitate of barium sulfate forms.

1. Write the balanced full molecular equation for this reaction.

2. Write the balanced net ionic equation for this reaction, ensuring all states of matter are explicitly included.

3. Identify the spectator ions in this chemical system.