Reactivity 3. What are the mechanisms of chemical change?

• Acid = proton donor • Base = proton acceptor • Deduce acid and base in a reaction; distinguish base and alkali

• Differ by one proton • Deduce conjugate acid/base formulas

• Can act as both acid and base • Write equations showing acid and base behaviour

• pH = −log₁₀[H⁺] • [H⁺] = 10⁻ᵖᴴ • Calculate pH and [H+]; include universal indicator and pH probe use

• Kw = [H⁺][OH⁻] • Acidic: [H⁺] > [OH⁻] • Neutral: [H⁺] = [OH⁻] • Basic: [H⁺] < [OH⁻] • Recognize acidic, neutral, and basic solutions from [H+] and [OH-]

• Differ in extent of ionization • Equilibrium favors weaker conjugate • Distinguish strong/weak from concentrated/dilute

• Acid + metal oxide/hydroxide/carbonate/hydrogencarbonate • Formulate equations and identify parent acids/bases of salts

• Strong acid-strong base titrations • Characteristic shapes • Sketch and interpret intercept and equivalence point for monoprotic titrations

• pOH = −log₁₀[OH⁻] • [OH⁻] = 10⁻ᵖᴼᴴ • pH + pOH = 14 (at 25°C) • Interconvert [H+], [OH-], pH, and pOH

• Ka, Kb, pKa, pKb • Interpret relative acid/base strength from Ka, Kb, pKa, and pKb

• Ka × Kb = Kw • Solve problems involving Ka, Kb, and Kw

• pH depends on parent acid/base strength • Write ion hydrolysis equations and predict salt solution pH

• Four combinations: strong-strong, strong-weak, weak-strong, weak-weak • Interpret buffer region and points where pH = pKa or pOH = pKb

• Weak acids with colored conjugate pairs • Color change at pH ≈ pKa • Write indicator equilibria and include universal indicator as a mixture

• End point coincides with equivalence point • Choose indicators from salt identity and indicator pH range; distinguish end point and equivalence point

• Resist pH change • Acidic buffers: weak acid + conjugate base • Basic buffers: weak base + conjugate acid • Explain buffer action using weak acid/base conjugate systems

• Buffer pH depends on pKa/pKb and acid/base to conjugate ratio • Solve buffer composition and pH problems using equilibrium constants • Explain the effect of dilution on buffer pH

• Electron transfer, oxidation state change • Oxygen gain/loss, hydrogen loss/gain • Oxidizing/reducing agents • Deduce oxidation states and identify oxidized/reduced species

• Separate oxidation and reduction • Show electron loss/gain • Deduce redox half-equations and equations in acidic or neutral solutions

• Metals: ease of oxidation • Halogens: ease of reduction • Metal displacement reactions • Predict metal oxidation and halogen reduction using supplied data

• Release H₂ gas • Deduce equations for reactive metals with dilute acids

• Oxidation at anode • Reduction at cathode • Signs/polarities in voltaic vs. electrolytic cells • Identify anode/cathode from electrode reactions

• Spontaneous redox → electrical energy • Electron flow: anode → cathode (external circuit) • Ion movement across salt bridge • Include metal/metal ion half-cells, circuit, and salt bridge

• Redox reactions reversible with electrical energy • Deduce charging reactions from discharge reactions and compare cell types

• Electrical energy → chemical energy • Non-spontaneous reactions • Electrolysis of molten salts • Explain current conduction and deduce molten salt electrolysis products

• Primary alcohols → aldehydes → carboxylic acids • Secondary alcohols → ketones • Include distillation/reflux setup and that tertiary alcohols are not oxidized similarly

• Carboxylic acids → aldehydes → primary alcohols • Ketones → secondary alcohols • Include hydride ion role; specific reducing agents and mechanisms are not assessed

• Addition of H₂ lowers unsaturation • Alkenes + H₂, alkynes + H₂ • Deduce hydrogenation products of alkenes and alkynes

• Hydrogen half-cell = 0 V by convention • Ease of oxidation/reduction • Use standard conditions and electrode potential data to compare oxidizing/reducing ability

• Calculate from E⦵ values • Positive E⦵cell = spontaneous • Predict feasible redox reactions from E⦵cell

• ΔG⦵ = −nFE⦵cell • Link electron number, Faraday constant, and spontaneity

• Competing reactions at electrodes • Water oxidation/reduction • Deduce products from standard electrode potentials; include water and aqueous solutions

• Electrolytic coating with metal layer • Explain the metal object as cathode and the coating metal as ion source

3.3.1Radicals

• Molecular entity with unpaired electron • Highly reactive • Recognize radical notation and high reactivity

3.3.2Homolytic fission

• Produces radicals • Halogens with UV light/heat (initiation step) • Use single-barbed arrows for single-electron movement

3.3.3Radical substitution

• Alkanes + halogens • Propagation and termination steps • Mixture of products • Write initiation, propagation, and termination equations

• Donate electron pair to electrophile • Recognize nucleophiles as electron-rich species

• Nucleophile donates pair, forms new bond • Another bond breaks, leaving group departs • Deduce substitution products from nucleophile and leaving group

• Both electrons stay with one fragment • Forms ions • Use curly arrows to show electron-pair movement

• Accept electron pair from nucleophile • Recognize electrophiles as electron-deficient species

• High electron density at C=C bond • Reactions: + H₂O, + halogens, + hydrogen halides • Deduce alkene addition equations; SL mechanisms are not assessed

• Lewis acid = electron-pair acceptor • Lewis base = electron-pair donor • Classify nucleophiles/electrophiles using Lewis acid-base theory

• Lewis base + Lewis acid • Nucleophiles = Lewis bases • Electrophiles = Lewis acids • Explain coordination bond formation with electron-pair donation

• Ligands donate electron pairs to transition metal cations • Identify ligands and central transition metal cations in complex ions

• Primary halogenoalkanes: SN2 • Tertiary halogenoalkanes: SN1 • Distinguish one-step SN2 and two-step SN1; include stereospecific SN2

• Identity influences rate • Link carbon-halogen bond enthalpy and polarity to reaction rate

• Symmetrical alkenes + halogens/water/HX • Describe mechanisms with curly arrows and carbocation/halonium intermediates as appropriate

• Unsymmetrical alkenes + HX or H₂O • Major product from more stable carbocation • Predict and explain major products from carbocation stability

• Mechanism with charged electrophile E⁺ • Formation of the electrophile is not assessed