Zumdahl’s Zumdahl’s Chapter 4Chapter 4

Chemical Reactions and Chemical Reactions and Solution StoichiometrySolution Stoichiometry

Chapter ContentsChapter Contents

WaterWater Aqueous SolutionsAqueous Solutions

ElectrolytesElectrolytes Strong and WeakStrong and Weak

NonelectrolytesNonelectrolytes Solution Solution

CompositionComposition Chemical Chemical

ReactionsReactions PrecipitationsPrecipitations

Describing ReactionsDescribing Reactions StoichiometryStoichiometry Acid-Base ReactionsAcid-Base Reactions

TitrationTitration Oxidation-ReductionOxidation-Reduction

Oxidation StatesOxidation States Balancing RedoxBalancing Redox

Half Reaction MethodHalf Reaction Method

Polar (covalent) Molecule Polar (covalent) Molecule (( = 1.4) = 1.4)

Hydration Hydration The tendency for salt to “fall apart” when The tendency for salt to “fall apart” when

strong positive and negative charges are strong positive and negative charges are replaced by water-ion interactionsreplaced by water-ion interactions

Hydration spheres cradle ionsHydration spheres cradle ions Hydrogen Bonding Hydrogen Bonding ( ( –H•••O– )–H•••O– )

O lone pair binds neighbor H O lone pair binds neighbor H (at ~ 15%)(at ~ 15%)

““Like dissolves like.”Like dissolves like.”

Water, HWater, H22O, O, Universal Universal SolventSolvent

ElectrolytesElectrolytes

Ions conduct electricityIons conduct electricity in proportion to their number in proportion to their number (& mobility)(& mobility)

Strong Electrolytes are Strong Electrolytes are fullyfully ionized. ionized. NaCl, HNONaCl, HNO33, Ca(OH), Ca(OH)22, MgSO, MgSO44, soap, etc., soap, etc.

Weak Electrolytes are Weak Electrolytes are mostlymostly molecular.molecular. Tap water, CHTap water, CH33COCO22H, (NHH, (NH44)OH, etc.)OH, etc.

Nonelectrolytes do Nonelectrolytes do notnot ionize. ionize. PurePure water, alcohols, sugars, etc. water, alcohols, sugars, etc.

Solution CompositionSolution Composition

Concentration as mol LConcentration as mol L––11 or or MMolarityolarity I.e., moles I.e., moles solutesolute per Liter of final per Liter of final solutionsolution

Alt., Alt., molalitymolality, moles solute per 1 kg solvent., moles solute per 1 kg solvent.

Dilution conserves number of molesDilution conserves number of moles CC11 V V11 = C = C22 V V22 solves dilution problems. solves dilution problems.

Molarity ideal for dispensing solutions.Molarity ideal for dispensing solutions. Controlled volume = controlled moles soluteControlled volume = controlled moles solute Convert to moles by CV, then apply rxn. stoich.Convert to moles by CV, then apply rxn. stoich.

Types of Chemical Types of Chemical ReactionsReactions

Categorized by motivational factors!Categorized by motivational factors! Le ChLe Châtlier: “âtlier: “Rxn. favors missing components.”Rxn. favors missing components.”

Gas Evolution Gas Evolution (gas leaves the solution (gas leaves the solution ))

Precipitation Precipitation (solid leaves the solution (solid leaves the solution ))

Weak electrolyte Weak electrolyte ((ionsions leave the solution) leave the solution) E.g., acid+base makes E.g., acid+base makes water!water!

Redox Redox (electrons find happiness)(electrons find happiness)

MEMORIZE THE MEMORIZE THE SOLUBILITY SOLUBILITY

TABLETABLE

NN choice. choice.

Description of Solution Description of Solution ReactionsReactions

Molecular Equations:Molecular Equations: HCl + KOH HCl + KOH KCl + H KCl + H22OO

Complete Ionic Equations:Complete Ionic Equations: HH++ + Cl + Cl–– + K + K++ + OH + OH–– K K++ + Cl + Cl–– + H + H22OO

Net Ionic EquationNet Ionic Equation:: HH++((aqaq) + OH) + OH––((aqaq) ) H H22O(O(ll))

Precipitation Precipitation StoichiometryStoichiometry

Write balanced net ionic reaction.Write balanced net ionic reaction. Determine limiting reactant.Determine limiting reactant.

Use Concentration Use Concentration Volume to get moles. Volume to get moles. Calculate product moles.Calculate product moles. If required, calculate leftover If required, calculate leftover

reactants.reactants. Use moles divided by Use moles divided by FinalFinal Volume to get Volume to get

concentration of leftovers.concentration of leftovers.

Acid – Base TitrationsAcid – Base Titrations

If at least one is “strong,” neutralization If at least one is “strong,” neutralization will be complete because Hwill be complete because H22O is very O is very ““weak!”weak!”

Choose indicator for strong visual signal Choose indicator for strong visual signal at completion.at completion.

For titrant, CV dispensed gives moles.For titrant, CV dispensed gives moles. Stoichiometry determines moles sampleStoichiometry determines moles sample Sample moles / sample vol = original Sample moles / sample vol = original MM

Oxidation – Reduction Oxidation – Reduction Reactions: REDOXReactions: REDOX

Oxidation: loss of electrons Oxidation: loss of electrons (e.g., metals)(e.g., metals)

Reduction: gain of electrons Reduction: gain of electrons (e.g., F(e.g., F22)) BOTH BOTH MUSTMUST OCCUR OCCUR (because electrons (because electrons

conserved)conserved)

Oxidizing Oxidizing AgentAgent gets Reduced gets Reduced (and (and converse)converse)

Oxidation States Oxidation States (imagine everything ionic)(imagine everything ionic) Add up to charge on speciesAdd up to charge on species Always zero for neutral elementsAlways zero for neutral elements

Solution Redox Solution Redox StoichiometryStoichiometry

Determine redox agentsDetermine redox agents Use Half Reaction MethodsUse Half Reaction Methods

Balance red- and ox- separately with eBalance red- and ox- separately with e––

Balance excess O with HBalance excess O with H22OO Balance excess H with HBalance excess H with H++

Scale each for equal number of Scale each for equal number of ee–– transfertransfer

Add & cancel (esp. Add & cancel (esp. ee––) equally left & right) equally left & right ““Titrate” equation algebraically Titrate” equation algebraically ifif OH OH––