1. Chemical Reactions and Solution Stoichiometry
Zumdahl’s Chapter 4
Chemical Reactions and Solution Stoichiometry

2. Chapter Contents Water Aqueous Solutions Solution Composition
Electrolytes
Strong and Weak
Nonelectrolytes
Solution Composition
Chemical Reactions
Precipitations
Describing Reactions
Stoichiometry
Acid-Base Reactions
Titration
Oxidation-Reduction
Oxidation States
Balancing Redox
Half Reaction Method

3. Water, H2O, Universal Solvent
Polar (covalent) Molecule ( = 1.4)
Hydration
The tendency for salt to “fall apart” when strong positive and negative charges are replaced by water-ion interactions
Hydration spheres cradle ions
Hydrogen Bonding ( –H•••O– )
O lone pair binds neighbor H (at ~ 15%)
“Like dissolves like.”

4. Electrolytes Ions conduct electricity
in proportion to their number (& mobility)
Strong Electrolytes are fully ionized.
NaCl, HNO3, Ca(OH)2, MgSO4, soap, etc.
Weak Electrolytes are mostly molecular.
Tap water, CH3CO2H, (NH4)OH, etc.
Nonelectrolytes do not ionize.
Pure water, alcohols, sugars, etc.

5. Solution Composition Concentration as mol L–1 or Molarity
I.e., moles solute per Liter of final solution
Alt., molality, moles solute per 1 kg solvent.
Dilution conserves number of moles
C1 V1 = C2 V2 solves dilution problems.
Molarity ideal for dispensing solutions.
Controlled volume = controlled moles solute
Convert to moles by CV, then apply rxn. stoich.

6. Types of Chemical Reactions
Categorized by motivational factors!
Le Châtlier: “Rxn. favors missing components.”
Gas Evolution (gas leaves the solution )
Precipitation (solid leaves the solution )
Weak electrolyte (ions leave the solution)
E.g., acid+base makes water!
Redox (electrons find happiness)

7. MEMORIZE THE SOLUBILITY TABLE
N choice.

8. Description of Solution Reactions
Molecular Equations:
HCl + KOH  KCl + H2O
Complete Ionic Equations:
H+ + Cl– + K+ + OH–  K+ + Cl– + H2O
Net Ionic Equation:
H+(aq) + OH–(aq)  H2O(l)

9. Precipitation Stoichiometry
Write balanced net ionic reaction.
Determine limiting reactant.
Use Concentration  Volume to get moles.
Calculate product moles.
If required, calculate leftover reactants.
Use moles divided by Final Volume to get concentration of leftovers.

10. Acid – Base Titrations
If at least one is “strong,” neutralization will be complete because H2O is very “weak!”
Choose indicator for strong visual signal at completion.
For titrant, CV dispensed gives moles.
Stoichiometry determines moles sample
Sample moles / sample vol = original M

11. Oxidation – Reduction Reactions: REDOX
Oxidation: loss of electrons (e.g., metals)
Reduction: gain of electrons (e.g., F2)
BOTH MUST OCCUR (because electrons conserved)
Oxidizing Agent gets Reduced (and converse)
Oxidation States (imagine everything ionic)
Add up to charge on species
Always zero for neutral elements

12. Solution Redox Stoichiometry
Determine redox agents
Use Half Reaction Methods
Balance red- and ox- separately with e–
Balance excess O with H2O
Balance excess H with H+
Scale each for equal number of e– transfer
Add & cancel (esp. e–) equally left & right
“Titrate” equation algebraically if OH–