Solubility Equilibria Solubility product (K sp ) – equilibrium constant; has only one value for a given solid at a given temperature. Solubility – an equilibrium position. Bi 2 S 3 (s) 2Bi 3+ (aq) + 3S 2– (aq)
Ksp Calc - examples Calculate the solubility of silver chloride in water. K sp = 1.6 × 10 –10 1.3×10 -5 M Calculate the solubility of silver phosphate in water. K sp = 1.8 × 10 –18 1.6×10 -5 M
Solubility in acid soln - 1 How does the solubility of silver chloride in water compare to that of silver chloride in an acidic solution (made by adding nitric acid to the solution)? Explain. The solubilities are the same.
Solubility in acid soln - 2 How does the solubility of silver phosphate in water compare to that of silver phosphate in an acidic solution (made by adding nitric acid to the solution)? Explain. Phosphate ion is the conjugate base of a weak acid – a somewhat strong base so it reacts with H+ The silver phosphate is more soluble in an acidic solution.
Solubility in other salt solns Calculate the solubility of AgCl (K sp = 1.6 × 10 –10 ) in: 100.0 mL of 4.00 x 10 -3 M calcium chloride. 2.0×10 -8 M 100.0 mL of 4.00 x 10 -3 M calcium nitrate. 1.3×10 -5 M
Precipitation (Mixing 2 Solutions of Ions) Q > K sp ; precipitation occurs and will continue until the concentrations are reduced to the point that they satisfy K sp. Q < K sp ; no precipitation occurs.
Precipitation? Flow chart for solving Precipitation questions
Selective Precipitation (mixtures of metal ions) Use a reagent whose anion forms a precipitate with only one or a few of the metal ions in the mixture. Example: Solution contains Ba 2+ and Ag + ions. Adding NaCl will form a precipitate with Ag + (AgCl), while still leaving Ba 2+ in solution.