Acid Base & Solubility Equilibria

Solubility equilibrium is a type of dynamic equilibrium that exists when a chemical compound in the solid state is in chemical equilibrium with a solution of that compound. The solid may dissolve unchanged, with dissociation, or with chemical reaction with another constituent of the solution, such as acid or alkali. Each solubility equilibrium is characterized by a temperature-dependent solubility product which functions like an equilibrium constant. Solubility equilibria are important in pharmaceutical, environmental and many other scenarios.

Course Contents

  • Acid dissociation constants, Ka and the use of pKa
  • Base dissociation constants, Kb and the use of pKb
  • The ionic product of water, Kw
  • pH: choice of pH indicators
  • Buffer solutions
  • Solubility product; the common ion effect and complex ion formation

Learning Outcomes

Candidates should be able to:

  • (a) explain qualitatively the differences in behaviour between strong and weak acids and bases in terms of the extent of dissociation
  • (b) explain the terms pH; Ka ; pKa ; Kb ; pKb ; Kw and apply them in calculations, including the relationship Kw =KaKb
  • (c) calculate (H+ (aq)) and pH values for strong acids, weak monobasic (monoprotic) acids, strong bases, and weak monoacidic bases [Calculations involving weak acids/bases will not require solving of quadratic equations]
  • (d) describe the changes in pH during acid-base titrations and explain these changes in terms of the strengths of the acids and bases
  • (e) explain the choice of suitable indicators for acid-base titrations, given appropriate data
  • (f) (i) explain how buffer solutions control pH
  • (ii) describe and explain their uses, including the role of H2CO3 /HCO3– in controlling pH in blood
  • (g) calculate the pH of buffer solutions, given appropriate data
  • (h) show understanding of, and apply, the concept of solubility product, Ksp
  • (i) calculate Ksp from concentrations and vice versa
  • (j) 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 Section 13)