25.1.8—Write an expression for Ksp
- Syllabus
- 9701–2028–2029
- Objective
- 25.1.8
- Level
- A2
Write Ksp by balancing the dissolution equation and omitting the solid
Write the saturated dissolution equilibrium first, then multiply aqueous-ion concentrations according to the coefficients. The undissolved solid has activity one and is not included.
Use parentheses for polyatomic ions and distinguish charges from stoichiometric powers. The expression is tied to the chosen dissolution direction.
Al(OH)₃(s) ⇌ Al³⁺ + 3OH⁻ gives Ksp=[Al³⁺][OH⁻]³; PbI₂(s) gives Ksp=[Pb²⁺][I⁻]².
Do not include [Al(OH)₃] or write powers from ionic charges instead of equation coefficients.
ConceptA-Level CAIE Chemistry A2