Zumdahl`s Chap. 4 - The University of Texas at Dallas
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Transcript Zumdahl`s Chap. 4 - The University of Texas at Dallas
Zumdahl’s
Chapter 4
Chemical Reactions and
Solution Stoichiometry
Chapter Contents
Water
Aqueous Solutions
Electrolytes
Strong and Weak
Nonelectrolytes
Solution
Composition
Chemical Reactions
Describing Reactions
Stoichiometry
Acid-Base Reactions
Precipitations
Oxidation-Reduction
Titration
Oxidation States
Balancing Redox
Half Reaction Method
Water, H2O, Universal Solvent
Polar (covalent) Molecule ( = 1.4)
Hydration (high dielectric constant)
Hydration spheres cradle ions
Electric field dampening reduces ppt
Hydrogen Bonding
( –H•••O– )
O lone pair binds neighbor H (at ~ 15%)
“Like dissolves like.”
Electrolytes
Ions conduct electricity
NaCl, HNO3, Ca(OH)2, MgSO4, soap, etc.
Weak Electrolytes are mostly molecular.
(& mobility)
Strong Electrolytes are fully ionized.
in proportion to their number
Tap water, CH3CO2H, (NH4)OH, etc.
Nonelectrolytes do not ionize.
Pure water, alcohols, sugars, etc.
Solution Composition
Concentration as mol L–1 or Molarity
I.e., moles solute per Liter of final solution
Dilution conserves number of moles
Alt., molality, moles solute per 1 kg solvent.
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.
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)
MEMORIZE THE
SOLUBILITY TABLE
N choice.
Description of Solution
Reactions
Molecular Equations:
Complete Ionic Equations:
HCl + KOH KCl + H2O
H+ + Cl– + K+ + OH– K+ + Cl– + H2O
Net Ionic Equation:
H+(aq) + OH–(aq) H2O(l)
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.
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
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
Memrize the algorithm.
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–