Chapter 14: Acid-Base Equilibria in Aqueous Solution

The Brønsted-Lowry model provides the primary framework, defining acids as proton donors and bases as proton acceptors, with emphasis on conjugate acid-base pairs and amphoteric species that can function in either role depending on environmental conditions. Water's self-ionization establishes the water ionization constant and underpins the logarithmic pH and pOH scales used to quantify hydrogen and hydroxide ion concentrations across many orders of magnitude. The strength of weak acids and bases is characterized through ionization constants and their logarithmic expressions, with the reciprocal relationship between conjugate acid and base strength determining solution behavior. The Lewis model extends acid-base theory by describing interactions in terms of electron pair donation and acceptance, enabling analysis of metal complexation and organic reactivity patterns visualized through electrostatic potential mapping. Quantitative analysis of weak acid and base solutions employs ICE tables and equilibrium expressions, while the common ion effect demonstrates how pre-existing ions suppress ionization in equilibrium systems. Speciation diagrams reveal how the relative proportions of protonated and deprotonated forms vary across the pH spectrum, with the critical principle that ionization states are equal when pH equals the acid's pKa value. Buffer solutions maintain relatively constant pH by containing significant quantities of a weak acid and its conjugate base, with buffer capacity determined by the Henderson-Hasselbalch equation and the concentrations of buffering species. Acid-base titrations serve as quantitative analytical techniques, with the pH at the equivalence point depending critically on the strength of the acid and base involved, while polyprotic systems and biological molecules like amino acids exhibit multiple ionizable groups that establish isoelectric points. The chapter emphasizes physiological relevance through discussion of blood buffering systems and the consequences of disruptions to acid-base homeostasis, connecting theoretical principles to real-world pharmaceutical bioavailability and clinical outcomes.