Presentation on theme: "Chemical Reactions and Solution Stoichiometry"— Presentation transcript:
1 Chemical Reactions and Solution Stoichiometry Zumdahl’s Chapter 4Chemical Reactions and Solution Stoichiometry
2 Chapter Contents Water Aqueous Solutions Solution Composition ElectrolytesStrong and WeakNonelectrolytesSolution CompositionChemical ReactionsPrecipitationsDescribing ReactionsStoichiometryAcid-Base ReactionsTitrationOxidation-ReductionOxidation StatesBalancing RedoxHalf Reaction Method
3 Water, H2O, Universal Solvent Polar (covalent) Molecule ( = 1.4)HydrationThe tendency for salt to “fall apart” when strong positive and negative charges are replaced by water-ion interactionsHydration spheres cradle ionsHydrogen 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 solutionAlt., molality, moles solute per 1 kg solvent.Dilution conserves number of molesC1 V1 = C2 V2 solves dilution problems.Molarity ideal for dispensing solutions.Controlled volume = controlled moles soluteConvert 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)
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 TitrationsIf 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 sampleSample 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 speciesAlways zero for neutral elements
12 Solution Redox Stoichiometry Determine redox agentsUse Half Reaction MethodsBalance red- and ox- separately with e–Balance excess O with H2OBalance excess H with H+Scale each for equal number of e– transferAdd & cancel (esp. e–) equally left & right“Titrate” equation algebraically if OH–