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Solubility Equilibria

Solubility Equilibria. Lead (II) iodide precipitates when potassium iodide is mixed with lead (II) nitrate. Graphic: Wikimedia Commons user PRHaney. K sp Values for Some Salts at 25 C. Solving Solubility Problems. For the salt AgI at 25 C , K sp = 1.5 x 10 -16.

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Solubility Equilibria

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  1. SolubilityEquilibria Lead (II) iodide precipitates when potassium iodide is mixed with lead (II) nitrate. Graphic: Wikimedia Commons user PRHaney

  2. Ksp Values for Some Salts at25C

  3. Solving Solubility Problems For the salt AgI at 25C, Ksp = 1.5 x 10-16 AgI(s)  Ag+(aq) + I-(aq) O O +x +x x x 1.5 x 10-16 = x2 x = solubility of AgI in mol/L = 1.2 x 10-8 M

  4. Solving Solubility Problems For the salt PbCl2 at 25C, Ksp = 1.6 x 10-5 PbCl2(s)  Pb2+(aq) + 2Cl-(aq) O O +2x +x 2x x 1.6 x 10-5 = (x)(2x)2 = 4x3 x = solubility of PbCl2 in mol/L = 1.6 x 10-2 M

  5. Solving Solubility Problems For the salt AgI at 25C, Ksp = 1.5 x 10-16 AgI(s)  Ag+(aq) + I-(aq) O O +x +x x x 1.5 x 10-16 = x2 x = solubility of AgI in mol/L = 1.2 x 10-8 M

  6. Predicting Precipitate Formation • Use the initial concentrations of ions in solution in the solubility product constant expression to calculate Qsp. • If Qsp < Kspthe solution is unsaturated and no precipitate will form. • If Qsp = Kspthe solution is saturated and no change will occur.

  7. Predicting Precipitate Formation, continued… • If Qsp > Kspa precipitate will form, reducing the concentrations of the ions in the solution until the product of their concentrations in the Ksp expression equals the numerical value of Ksp.

  8. Predicting Precipitate Formation, continued… Do practice problems on pg. 619

  9. Predicting Precipitate Formation, continued… Answers: 25. a. Qsp > Ksp so a precipitate of PbF2 will form. b. Qsp < Ksp so no precipitate will form 26. A precipitate will form.

  10. The Common Ion Effect • Why is PbCrO4 less soluble in aqueous solution of K2CrO4 than in pure water? • The K2CrO4 solution contains CrO42– ions before any PbCrO4 dissolves.

  11. The Common Ion Effect (cont.) • A common ion is an ion that is common to two or more ionic compounds. • The lowering of the solubility of a substance because of the presence of a common ion is called the common ion effect.

  12. Solving Solubility with a Common Ion For the salt AgI at 25C, Ksp = 1.5 x 10-16 What is its solubility in 0.05 M NaI? AgI(s)  Ag+(aq) + I-(aq) 0.05 O 0.05+x +x 0.05+x x 1.5 x 10-16 = (x)(0.05+x)  (x)(0.05) x = solubility of AgI in mol/L = 3.0 x 10-15 M

  13. Precipitation and Qualitative Analysis

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