Proton-transfer and electron-transfer chemistry: Bronsted-Lowry acid-base definition, pH, redox half-reactions, standard electrode potentials. Operational core of electrochemistry and biochemistry.
acids-bases-redox
Brønsted-Lowry acid-base
An acid is a proton (H⁺) donor; a base is a proton acceptor. Every acid-base reaction is a proton transfer between a conjugate acid-base…
pH scale
Logarithmic measure of hydrogen-ion activity: pH = -log₁₀ a_{H⁺}. Neutral water at 25 °C has pH 7.00. Convenient operational handle on…
Oxidation-reduction (redox)
Coupled electron-transfer reactions: one species is oxidised (loses electrons; oxidation number increases) while another is reduced (gains…
Standard electrode potential (E°)
Equilibrium potential of a half-cell reaction under standard conditions (1 M, 1 bar, 25 °C) referenced to the standard hydrogen electrode…
Acid-base indicator colour change
Indicator molecules (e.g. litmus, phenolphthalein, bromothymol blue) shift between protonated and deprotonated forms with different…
Arrhenius acid-base theory
An acid is a substance that increases [H⁺] when dissolved in water; a base is one that increases [OH⁻]. The earliest of the three standard…
Lewis acid-base theory
An acid is an electron-pair acceptor; a base is an electron-pair donor. The most general of the three acid-base theories (G.N. Lewis 1923).…
Acid dissociation constant (Kₐ)
Equilibrium constant for the dissociation HA + H₂O ⇌ A⁻ + H₃O⁺. Kₐ = [A⁻][H₃O⁺] / [HA]; pKₐ = −log₁₀ Kₐ. Large Kₐ (small pKₐ) = strong…
Water autoionization (Kw)
Pure water undergoes self-ionization 2 H₂O ⇌ H₃O⁺ + OH⁻ with Kw = [H₃O⁺][OH⁻] = 1.0×10⁻¹⁴ at 25 °C. Implies pH + pOH = 14 in dilute aqueous…
Buffer solution
A solution that resists changes in pH upon addition of small amounts of acid or base. Typically an aqueous mixture of a weak acid (HA) and…
Titration
Quantitative analytical procedure in which a reagent of known concentration (the titrant) is added incrementally to a solution of unknown…
Oxidation state (oxidation number)
A bookkeeping integer (or fraction) assigned to each atom in a compound that tracks the hypothetical charge it would carry if all bonds…
HSAB (Hard/Soft Acid/Base)
Hard acid + hard base, soft + soft give stable complexes; quantified by absolute hardness η = (I-A)/2; explains selectivity.
pKa, pKb & water leveling
Strongest acid in H₂O is H₃O⁺; pKa<0 leveled; pKa differentiation requires stronger solvents (DMSO scale); Bordwell tables.
Hammett acidity function H₀
H₀ = pKa_BH⁺ - log[BH⁺/B] extends pH for concentrated acids; H₀(H₂SO₄ 100%) ≈ -12; magic acid H₀ ≈ -24.
Superacids & magic acid
H > H₂SO₄ (H₀ < -12); Olah's FSO₃H·SbF₅ protonates alkanes; carborane acid HCB₁₁Cl₁₁ strongest isolable (2004 Nobel).
Frost (oxidation-state) diagrams
Plot nE° vs oxidation state; slopes show redox stability; disproportionation indicated by concave points.
Latimer diagrams
Chain of E° values between oxidation states; compute any potential by weighted average; analyze stability domains.
Pourbaix (E vs pH) diagram
Thermodynamic stability regions in E–pH plane; immunity, passivation, corrosion zones; water stability limits.
Disproportionation/comproportionation
2 Cu⁺ → Cu + Cu²⁺ disproportionation in H₂O; reverse comproportionation; driven by thermodynamic stability.
Arrhenius electrolytic dissociation
Strong vs weak electrolytes; degree α; Kohlrausch law of independent ionic migration; van 't Hoff factor i.
General acid/base catalysis
Rate involves BH⁺ / B⁻ transfer in TS; Brønsted plot α distinguishes specific vs general; pivotal in enzyme mechanism.
Photoredox catalysis
Visible-light-excited Ru/Ir/organic PCs mediate single-electron transfer; couples with H-atom transfer, radical chemistry.
Concentration cells (Nernst limit)
EMF from activity gradient with same electrodes; E = (RT/nF) ln(a₂/a₁); used in glass pH electrodes, ion-selective sensors.
Redox titration endpoints
Permanganimetric, dichromate, Cu iodometry; potentiometric detection; MnO₄⁻/Mn²⁺, I₂/I⁻ self-indicating systems.
Bipolar membrane electrodialysis
Water-splitting membrane produces H⁺ and OH⁻ for acid/base regeneration; clean industrial deacidification.
Buffer capacity β = dCb/dpH
β = 2.303(Kw/[H⁺] + [H⁺] + Σ C_i K_i[H⁺]/(K_i+[H⁺])²); max at pH = pKa; design of biological buffers.