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Zumdahl’s Chapter 4

Zumdahl’s Chapter 4

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Zumdahl’s Chapter 4

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

  2. 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 Chapter Contents

  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 ( –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 • 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–