Lecture Notes: Molecular, Ionic, and Net Ionic Equations

Overview

• Transition from molecular to ionic equations involves splitting cations from anions.
• Example focused on lead (II) nitrate and ammonium sulfide.

Key Chemical Concepts

Lead (II) Nitrate

• Lead (II) nitrate consists of lead cations ( \text{Pb}^{2+} ) and nitrate anions ( \text{NO}_3^- ).
• Subscripts indicate the number of ions; e.g., two nitrate ions per lead cation.
• Phases are important; aqueous phase for both lead and nitrate._

Ammonium Sulfide

• Sulfide ( \text{S}^{2-} ) forms a 2- anion.
• Ammonium ( \text{NH}_4^+ ) is a polyatomic cation.
• Phases remain aqueous._

Reaction Outcomes

Ammonium Nitrate

• Remains aqueous; soluble due to ammonium.
• Stoichiometry: two ammonium ions and two nitrate ions.

Lead (II) Sulfide

• Does not split; remains solid (precipitate) in ionic equations.

Spectator Ions and Net Ionic Equations

• Spectator ions (nitrates and ammonium) do not participate in the reaction.
• Net ionic equation arises by removing spectator ions.
• Describes the chemistry in the reaction: formation of a solid precipitate.

Sample Problem

• Reaction Example: Chromium (III) Chloride and Sodium Hydroxide
  • Write chemical formulas from names.
  • Chromium (III) Chloride: ( \text{CrCl}_3 )
  • Sodium Hydroxide: ( \text{NaOH} )_

Predicting and Balancing Reactions

• Identify double displacement reactions.
• Predict products: swap anions.
• Solubility rules help identify phase states (aqueous vs. solid).
• Balance equations using stoichiometric coefficients.

Ionic Equations

• Molecular to ionic equation involves splitting aqueous compounds into ions.
• Solids remain intact in ionic equations.

Example Balance

• Sodium chloride is aqueous, balanced with stoichiometry.
• Chromium hydroxide forms a solid precipitate.

Completing the Net Ionic Equation

• Remove spectator ions (sodium and chloride in this example).
• Ensure charges and atoms are balanced.

Important Steps for Solving Reaction Equations

1. Write molecular equations and predict products.
2. Use solubility rules to determine phases.
3. Balance the equations.
4. Split into ionic equations.
5. Identify and remove spectator ions to derive the net ionic equation.
6. Check balance of atoms and charges.

Participation Questions

• Ammonium Carbonate and Calcium Chloride

  • Write molecular, complete ionic, net ionic equations.
  • Determine precipitate formula.

• Sodium Sulfate and Silver Acetate

  • Write molecular, complete ionic, net ionic equations.
  • Identify spectator ions.

Tips for Solving

• Ensure clarity in predicting products and balancing equations.
• Understand solubility rules and their exceptions.
• Always verify atom and charge balance.

If you have questions, don’t hesitate to ask. Have a great afternoon!