Unit 7 - Chpt 16 - Solubility equilibria and Quantitative analysis

• Solubility equilibria and Ksp• Predict precipitation

• HW set1: Chpt 16 - pg. 766-771 # 19, 21, 23, 28, 33, 40, 43, 45, 50 - Due Thurs. Mar 21

• Rev Problems: Chpt 16 - pg. 766-771 # - 25, 35, 56

Solubility Equilibria

• Solubility product (Ksp) – equilibrium constant; has only one value for a given solid at a given temperature.

• Solubility – an equilibrium position.

Bi2S3(s) 2Bi3+(aq) + 3S2–(aq)

Ksp values for some compounds

Ksp Calc - examples

Calculate the solubility of silver chloride in water. Ksp = 1.6 × 10–10

1.3×10-5 M

Calculate the solubility of silver phosphate in water. Ksp = 1.8 × 10–18

1.6×10-5 M

Solubility in acid sol’n - 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 sol’n - 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 sol’ns

Calculate the solubility of AgCl (Ksp = 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 > Ksp; precipitation occurs and will continue until the concentrations are reduced to the point that they satisfy Ksp.

• Q < Ksp; 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 Ba2+ and Ag+ ions. Adding NaCl will form a precipitate with

Ag+ (AgCl), while still leaving Ba2+ in solution.