Overview
This lecture explains how to write net ionic equations for reactions in solution, focusing on identifying soluble and insoluble compounds, spectator ions, and special cases involving gas evolution.
Steps for Writing Net Ionic Equations
- Write soluble compounds as separate ions; insoluble/special compounds as full formulas.
- Identify which ions combine to form an insoluble precipitate, gas, or weak acid/base.
- Spectator ions (not participating in the reaction) are omitted from the net ionic equation.
- Swap ion partners to determine possible new compounds and test for insolubility using solubility rules.
Example Problems and Key Takeaways
- Mixing barium nitrate and sodium sulfate forms insoluble barium sulfate; sodium and nitrate ions are spectators.
- Combining potassium chloride and silver nitrate yields insoluble silver chloride; potassium and nitrate are spectators.
- Mixing calcium nitrate and zinc chloride results in no reaction, as all possible products are soluble—no precipitate forms.
- Potassium phosphate and lead(II) nitrate form insoluble lead(II) phosphate; potassium and nitrate are spectators. Always balance net ionic equations.
Gas Evolution Reactions & Special Cases
- Some products (carbonic acid, sulfurous acid, ammonium hydroxide) decompose to produce gases and water instead of existing as compounds.
- Carbonic acid (H2CO3) decomposes into CO2 (gas) and H2O (liquid).
- Sulfurous acid (H2SO3) decomposes into SO2 (gas) and H2O (liquid).
- Ammonium hydroxide (NH4OH) decomposes into NH3 (gas) and H2O (liquid).
Additional Gas Evolution Examples
- Mixing solid sodium bicarbonate (baking soda) and acetic acid (vinegar) produces CO2 (gas), H2O (liquid), Na+ (aq), and acetate (aq).
- Mixing sodium hydroxide solution and ammonium chloride solution produces NH3 (gas), H2O (liquid), Na+ (aq), and Cl– (aq).
Key Terms & Definitions
- Net Ionic Equation — An equation showing only the ions and molecules directly involved in a chemical reaction.
- Spectator Ion — Ions present in solution that do not participate directly in a chemical reaction.
- Solubility Rules — Guidelines to predict whether a compound will dissolve in water.
- Gas Evolution Reaction — A reaction in which a gas is formed as a product and escapes from the solution.
Action Items / Next Steps
- Review and memorize solubility rules for predicting precipitates.
- Practice balancing net ionic equations, including for gas evolution reactions.
- Prepare for the next lesson on non-solution reactions.