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Solubility Product Constant Factors Affecting Solubility Selective Precipitation

Solubility Product Constant Factors Affecting Solubility Selective Precipitation. Objectives Today I will be able to: Calculate the solubility product constant for a compound Explain the factors that affect solubility

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Solubility Product Constant Factors Affecting Solubility Selective Precipitation

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  1. Solubility Product ConstantFactors Affecting SolubilitySelective Precipitation

  2. Objectives • Today I will be able to: • Calculate the solubility product constant for a compound • Explain the factors that affect solubility • Determine the compounds that selectively precipitate from a solution when placed under stresses • Informal assessment – monitoring student interactions and questions as they complete the practice problems • Formal assessment – analyzing student responses to the practice problems

  3. Lesson Sequence • Evaluate: Warm Up • Explain: Notes • Elaborate: Practice Problems • Evaluate: Exit Ticket

  4. Warm Up

  5. Objectives • Today I will be able to: • Calculate the solubility product constant for a compound • Explain the factors that affect solubility • Determine the compounds that selectively precipitate from a solution when placed under stresses

  6. Homework • Continue working practice problems • Ch. 17 • 49, 51,53, 55, 57,59 • 69,70, 75,76

  7. Agenda • Warm Up • Notes • Practice Problems • Exit Ticket

  8. Solubility Product ConstantFactors Affecting SolubilitySelective Precipitation Notes

  9. Solubility Equilibria

  10. BaSO4(s) Ba2+(aq) + SO42−(aq) Solubility Product Constant • Consider the equilibrium that exists in a saturated solution of BaSO4 in water:

  11. Solubility Product Constant Expression The equilibrium constant expression for this equilibrium is Ksp = [Ba2+] [SO42−] where the equilibrium constant, Ksp, is called the solubility product.

  12. Ksp is not the same as solubility

  13. What is solubility? What is Ksp? • Solubility is generally expressed as the mass of solute dissolved in 1 L (g/L) or 100 mL (g/mL) of solution, or in mol/L (M). • Equilibrium constant for equilibrium between an ionic sold and its saturated solution • Unitless • Larger magnitude means more dissolving occurred • Only one value per temperature • Does not change with pH or other ions present in solution like solubility

  14. Calculation • Solid silver chromate is added to pure water at 25oC and some solid remains undissolved. The mixture is stirred for several days to ensure that equilibrium is achieved between the undissolved Ag2CrO4 and the solution. Analysis of the equilibrated solution shows that its silver ion concentration is 1.3 x 10-4 M. Assuming that the Ag2CrO4 solution is saturated , calculate Ksp for the compound.

  15. Calculation • The Ksp of CaF2 is 3.9 x 1o-11 at 25oC. Assuming equilibrium is established between solid and dissolved CaF2, calculate the solubility of CaF2 in grams/liter

  16. Factors impacting solubility

  17. BaSO4(s) Ba2+(aq) + SO42−(aq) 1. Common Ion Effect • If one of the ions in a solution equilibrium is already dissolved in the solution, the equilibrium will shift to the left and the solubility of the salt will decrease

  18. 2. pH • If a substance has a basic anion, it will be more soluble in an acidic solution. • Substances with acidic cations are more soluble in basic solutions.

  19. 3. Complex Ions • Complex Ions • Metal ions can act as Lewis acids and form complex ions with Lewis bases in the solvent.

  20. 4. Amphoterism • Amphoteric metal oxides and hydroxides are soluble in strong acid or base, because they can act either as acids or bases. • Examples of such cations are Al3+, Zn2+, and Sn2+

  21. Complex Ions Cont. • The formation of these complex ions increases the solubility of these salts.

  22. Precipitation and Separation of Ions

  23. Will a Precipitate Form? • In a solution, • If Q = Ksp, the system is at equilibrium and the solution is saturated. • If Q < Ksp, more solid will dissolve until Q = Ksp. • If Q > Ksp, the salt will precipitate until Q = Ksp.

  24. Sample Calculation • The Ksp for BaSO4 is 1.1 x 10¯10 and that for BaSeO4 is 2.8 x 10¯11. A 1.0 M solution of BaCl2 is added slowly to a solution that is 1.0 x 10¯4 M in sodium sulfate, Na2SO4 and 1.0 x 10¯4 M in sodium selenate, Na2SeO4. What is the approximate percentage of one anion has precipitated at the point which the second anion just begins to precipitate? (Assume the addition of the BaCl2 solution does not change the overall solution volume to any significant degree.)

  25. Solution

  26. Selective Precipitation of Ions One can use differences in solubilities of salts to separate ions in a mixture.

  27. Selective Precipitation Practice Problems • Visit the website and walk through the sample calculations • Try to solve the problem on your own and then walk through the worked out solution • http://www.chemteam.info/Equilibrium/SelectivePrecip.html

  28. Practice Problems Ch. 17 49, 51,53, 55, 57,59 69,70, 75,76

  29. Closure • Which problem did you find most challenging today?

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