Overview
This lecture covers solubility, precipitation reactions, how to predict if a precipitate forms using a solubility table, and how to write molecular, ionic, and net ionic equations for these reactions.
Solubility and Aqueous Solutions
- Aqueous (aq) means a compound is dissolved in water.
- Soluble ionic compounds dissociate into their ions in aqueous solution.
- Use a solubility table to determine if compounds are soluble (aq) or insoluble (s).
Precipitation Reactions
- Mixing two aqueous solutions may result in a solid; this solid is called a precipitate.
- A precipitation reaction occurs when combining two soluble salts forms an insoluble compound.
- If all products are soluble, no solid forms and no reaction occurs.
Predicting Precipitation
- Double replacement reactions involve swapping cations between compounds.
- Check product solubility using the solubility table; solids indicate precipitate formation.
- Example: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq); AgCl is insoluble and precipitates.
Writing Chemical Equations
- Molecular equation: Shows compounds before dissociation, including their phases.
- Ionic equation: Splits all aqueous compounds into their ions; solids and liquids stay intact.
- Net ionic equation: Cancels spectator ions, showing only the ions forming the precipitate.
Example Reactions
- AgNO₃(aq) + NaCl(aq): Spectator ions Na⁺ and NO₃⁻ are removed in the net ionic equation: Ag⁺(aq) + Cl⁻(aq) → AgCl(s).
- Na₂CO₃(aq) + CuCl₂(aq): Results in CuCO₃(s) precipitation; net ionic: Cu²⁺(aq) + CO₃²⁻(aq) → CuCO₃(s).
Key Terms & Definitions
- Aqueous (aq) — dissolved in water.
- Solubility table — chart predicting whether compounds are soluble or insoluble.
- Precipitate — solid formed from a reaction in solution.
- Precipitation reaction — reaction where two solutions form an insoluble solid.
- Molecular equation — equation showing compounds before ionization.
- Ionic equation — equation showing dissociated ions for aqueous compounds.
- Net ionic equation — equation showing only ions involved in forming the precipitate.
- Spectator ions — ions unchanged on both sides of the ionic equation.
Action Items / Next Steps
- Review and practice using the solubility table to predict precipitates.
- Practice writing molecular, ionic, and net ionic equations for precipitation reactions.
- Watch suggested videos and complete extra practice in the exam 3 materials.