hichem belarbi

This chapter provides a comprehensive and pedagogical exploration of solution chemistry, with a strong emphasis on acid-base equilibria and their analytical applications. It begins by establishing the fundamental concepts of aqueous solutions, including various concentration units and the unique properties of water as a solvent, notably its polarity, hydrogen bonding, and autoprotolysis.

The core of the chapter is dedicated to a rigorous study of acid-base equilibria. It introduces the Brønsted-Lowry theory, the classification of acids and bases (strong vs. weak, based on chemical nature and proton count), and the key constants 𝐾𝑎, 𝐾𝑏​, and 𝑝𝐾𝑎​. A detailed, step-by-step methodology is provided for calculating the pH of various solutions, including strong/weak acids and bases, buffer solutions, and mixtures, with special attention given to the validity of approximations and the crucial role of water's autoprotolysis in very dilute solutions.

The analytical power of these concepts is demonstrated through an extensive section on acid-base titrations. Using a clear and engaging "duel" analogy, the chapter systematically analyzes the four characteristic zones of titration curves for four fundamental cases: strong acid–strong base, weak acid–strong base, weak base–strong acid, and weak acid–weak base. It introduces the Henderson-Hasselbalch equation for buffer solutions and explains the role of the pH jump at the equivalence point. The chapter is enriched with numerous solved application exercises, linking the theoretical principles to practical clinical and pharmaceutical contexts (e.g., drug pKa, buffered vitamin C formulations).

Keywords: Solution Chemistry, Acid-Base Equilibria, pH Calculation, Buffer Solutions, Henderson-Hasselbalch Equation, Titration, Equivalence Point, Stoichiometry, Analytical Chemistry, Pharmaceutical Applications.