SAJC 2026 Solubility Equilibria Lecture Notes (Student)

St. Andrew’s Junior College JC2 H2 Chemistry 2026 1 St Andrew’s Junior College H2 Chemistry 2026 Lecture Notes 20 Solubility Equilibria Assessment Objectives: Candidates should be able to: (a) show understanding of, and apply, the concept of solubility product, Ksp (b) calculate Ksp from concentrations and vice versa. (c) discuss the effects on the solubility of ionic salts by the following: (i) common ion effect (ii) formation of complex ion, as exemplified by the reactions of halide ions with aqueous silver ions followed by aqueous ammonia (see also an Introduction to the Chemistry of Transition Elements) Lecture Outline 1. Solubility and Solubility Product 2. Precipitation and Ionic Product 3. Factors affecting solubility SLS Resources (req @students.edu.sg login) Lesson 1: Solubility and Solubility Product Lesson 2: Precipitation of Sparingly Soluble Salts Lesson 3: Common Ion Effect https://vle.learning.moe.edu.sg/moe- library/module/view/99023736-991d- 4605-a652-df3a6f984c25 https://vle.learning.moe.edu.sg/moe- library/module/view/ed3826a7-ce8c- 4140-97eb-fb189c6f077a https://vle.learning.moe.edu.sg/moe- library/module/view/c29629d4-141c- 4284-8f43-367950bf8405

St. Andrew’s Junior College JC2 H2 Chemistry 2026 2 1. SOLUBILITY AND SOLUBILITY PRODUCT Salts can be classified as soluble or insoluble. But even “insoluble” salts dissolve to a very small extent in water. A saturated solution is a solution in which the maximum amount of solute/salt has been dissolved. A saturated solution of an insoluble salt usually has a concentration of less than 0.001 mol dm –3. Contrast this to a saturated solution of sodium chloride, which has a concentration of 6.15 mol dm–3 For this chapter on solubility equilibrium, we will use the term “sparingly soluble” to describe insoluble salts. Soluble Sparingly soluble All nitrates NIL Most halides Halides of Pb2+, Ag+ and Cu+ Most sulfates Sulfates of Ba2+, Pb2+ and Ca2+ Oxides and hydroxides of Na+, K+, NH4+ and the larger group 2 cations such as Ca2+, Sr2+ and Ba2+ Most oxides and hydroxides Carbonates of Na+, K+ and NH4+ Most carbonates Chromates of Na+, K+ and NH4+ Most chromates Table 1: Soluble and sparingly soluble salts (no need to memorise!!!!) 1.1 Solubility product When a sparingly soluble salt e.g. AgCl solid is added slowly to pure water, it initially dissolves, but will eventually reach a point when no further solid dissolves and undissolved solid is seen. At this point, a saturated solution is formed. The ions in the saturated solution are in dynamic equilibrium with the excess undissolved solid. This means that the ions move from the solid to the saturated solution at the same rate as they move from the solution to the solid. AgCl(s) ⇌ Ag+(aq) + Cl–(aq) We can wr