Solutions

This chapter deals with the composition, behaviour, and properties of homogeneous mixtures called solutions. It explains different types of solutions (solid, liquid, gas) and various ways of expressing concentration such as mass percentage, volume percentage, mole fraction, molarity, and molality. The concept of solubility is discussed along with factors affecting it, including temperature and pressure, and Henry’s law for gases (p = kᴴx). The chapter introduces vapour pressure of liquid solutions and Raoult’s law (p₁ = X₁p₁°), distinguishing between ideal and non-ideal solutions and explaining deviations and azeotropes. A major focus is on colligative properties—relative lowering of vapour pressure, elevation of boiling point (ΔT_b = K_bm), depression of freezing point (ΔT_f = K_fm), and osmotic pressure (π = CRT)—which depend only on the number of solute particles. It also covers determination of molar mass using these properties and explains abnormal molar mass through association or dissociation using the van’t Hoff factor (i). Overall, the chapter builds a quantitative framework connecting solution concentration, intermolecular interactions, and thermodynamic properties.