Zumdahl

1
Zumdahls Chapter 4

• Chemical Reactions and Solution Stoichiometry

2
Chapter Contents

• Water
• Aqueous Solutions
• 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 (high dielectric constant)
• Hydration spheres cradle ions
• Electric field dampening reduces ppt
• Hydrogen Bonding ( HO )
• 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 L1 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., acidbase 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
• Mem?rize the algorithm.

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