Transcript Zumdahl’s Chap. 4

Zumdahl’s
Chapter 4
Chemical Reactions and
Solution Stoichiometry
Chapter Contents
Water
 Aqueous Solutions
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Electrolytes
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Strong and Weak
Nonelectrolytes
Solution
Composition
 Chemical Reactions
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Describing Reactions
 Stoichiometry
 Acid-Base Reactions
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Precipitations
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Oxidation-Reduction
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Titration
Oxidation States
Balancing Redox
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Half Reaction Method
Water, H2O, Universal Solvent
Polar (covalent) Molecule
 Hydration
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( = 1.4)
The tendency for salt to “fall apart” when
strong positive and negative charges are
replaced by water-ion interactions
 Hydration spheres cradle ions
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Hydrogen Bonding
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( –H•••O– )
O lone pair binds neighbor H (at ~ 15%)
“Like dissolves like.”
Electrolytes
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Ions conduct electricity
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NaCl, HNO3, Ca(OH)2, MgSO4, soap, etc.
Weak Electrolytes are mostly molecular.
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(& mobility)
Strong Electrolytes are fully ionized.
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in proportion to their number
Tap water, CH3CO2H, (NH4)OH, etc.
Nonelectrolytes do not ionize.
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Pure water, alcohols, sugars, etc.
Solution Composition
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Concentration as mol L–1 or Molarity
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I.e., moles solute per Liter of final solution
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Dilution conserves number of moles
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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.
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Types of Chemical Reactions
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Categorized by motivational factors!
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Le Châtlier: “Rxn. favors missing components.”
Gas Evolution (gas leaves the solution )
 Precipitation (solid leaves the solution )
 Weak electrolyte (ions leave the solution)
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E.g., acid+base makes water!
Redox
(electrons find happiness)
MEMORIZE THE
SOLUBILITY TABLE
N choice.
Description of Solution
Reactions
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Molecular Equations:
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Complete Ionic Equations:
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HCl + KOH  KCl + H2O
H+ + Cl– + K+ + OH–  K+ + Cl– + H2O
Net Ionic Equation:
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H+(aq) + OH–(aq)  H2O(l)
Precipitation Stoichiometry
Write balanced net ionic reaction.
 Determine limiting reactant.
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Use Concentration  Volume to get moles.
Calculate product moles.
 If required, calculate leftover reactants.
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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
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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)
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Add up to charge on species
 Always zero for neutral elements
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Solution Redox Stoichiometry
Determine redox agents
 Use Half Reaction Methods
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Balance red- and ox- separately with e–
Balance excess O with H2O
 Balance excess H with H+
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Scale each for equal number of e– transfer
 Add & cancel (esp. e–) equally left & right
 “Titrate” equation algebraically if OH–
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