2. 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) Bi3+(aq) + 3S2–(aq)
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3. Explain. If yes, explain and verify. If no, provide a counter-example.
CONCEPT CHECK!
In comparing several salts at a given temperature, does a higher Ksp value always mean a higher solubility?
Explain. If yes, explain and verify. If no, provide a counter-example.
No. In order to relate Ksp values to solubility directly, the salts must contain the same number of ions. For example, for a binary salt, Ksp = s2 (s = solubility); for a ternary salt, Ksp = 4s3.
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4. EXERCISE!
Calculate the solubility of silver chloride in water. Ksp = 1.6 × 10–10
Calculate the solubility of silver phosphate in water. Ksp = 1.8 × 10–18
a) 1.3×10-5 M
b) 1.6×10-5 M
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5. Calculate the solubility of AgCl in:
EXERCISE!
Calculate the solubility of AgCl in:
Ksp = 1.6 × 10–10
100.0 mL of 4.00 x 10-3 M calcium chloride.
100.0 mL of 4.00 x 10-3 M calcium nitrate.
a) 2.0×10-8 M Note: [Cl-] in CaCl2 is twice the [CaCl2] given mL is not used in the calculation.
b) 1.3×10-5 M
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6. Precipitation (Mixing Two 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.
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7. 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.
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8. Separation of Cu2+ and Hg2+ from Ni2+ and Mn2+ using H2S
At a low pH, [S2–] is relatively low and only the very insoluble HgS and CuS precipitate.
When OH– is added to lower [H+], the value of [S2–] increases, and MnS and NiS precipitate.
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