Chapter 16: Acids and Bases

Acids and Bases introduces the Brønsted-Lowry framework, defining acids as proton donors and bases as proton acceptors, which establishes the vital concept of conjugate acid-base pairs and the nature of amphiprotic substances like water that can function as either. The text delves into the autoionization of water, the thermodynamic ion product constant, and the mathematical foundations of the pH and pOH scales used to rigorously quantify the acidity, basicity, or neutrality of aqueous solutions. Students are guided through the chemical equilibrium of these systems, exploring acid ionization constants and base ionization constants to distinguish between strong electrolytes that dissociate completely and weak electrolytes that undergo only partial ionization. The chapter emphasizes practical equilibrium calculations utilizing ICE (Initial, Change, Equilibrium) tables and strategic simplifying assumptions to mathematically determine the degree and percentage of chemical ionization. Further complexity is introduced through the study of polyprotic acids, which ionize in multiple successive steps with decreasing acid strength. The curriculum also tackles advanced equilibrium models by employing material balance and electroneutrality (charge balance) equations for simultaneous and consecutive reactions. The phenomenon of salt hydrolysis is thoroughly explained, demonstrating how specific cations and anions act as weak acids or bases, intrinsically linking the ionization constants of conjugate pairs to predict the resulting pH of salt solutions. Crucially, the text explores the periodic and structural trends that govern chemical behavior, showing how molecular structure, bond length, heterolytic bond dissociation energy, bond polarity, electronegativity, terminal oxygen counts, and electron delocalization (resonance) dictate the relative strength across binary acids, oxoacids, organic carboxylic acids, and aromatic amines. Finally, the chapter broadens the chemical perspective by presenting the Lewis acid-base theory, characterizing acids as electron-pair acceptors and bases as electron-pair donors, which is essential for understanding coordinate covalent bonding, adduct formation, and the inherently acidic behavior of hydrated transition metal complex ions.