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
Lesson Sequence Evaluate: Warm Up Explain: Notes Elaborate: Practice Problems Evaluate: Exit Ticket
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
Homework Continue working practice problems Ch. 17 49, 51,53, 55, 57,59 69,70, 75,76
Agenda Warm Up Notes Practice Problems Exit Ticket
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
Calculation Solid silver chromate is added to pure water at 25 o C and some solid remains undissolved. The mixture is stirred for several days to ensure that equilibrium is achieved between the undissolved Ag 2 CrO 4 and the solution. Analysis of the equilibrated solution shows that its silver ion concentration is 1.3 x 10 -4 M. Assuming that the Ag 2 CrO 4 solution is saturated, calculate Ksp for the compound.
Calculation The K sp of CaF 2 is 3.9 x 1o -11 at 25 o C. Assuming equilibrium is established between solid and dissolved CaF 2, calculate the solubility of CaF 2 in grams/liter
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 BaSO 4 (s) Ba 2+ (aq) + SO 4 2− (aq)
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.
3. Complex Ions Complex Ions ▫Metal ions can act as Lewis acids and form complex ions with Lewis bases in the solvent.
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 Al 3+, Zn 2+, and Sn 2+
Complex Ions Cont. The formation of these complex ions increases the solubility of these salts.
Will a Precipitate Form? In a solution, ▫If Q = K sp, the system is at equilibrium and the solution is saturated. ▫If Q < K sp, more solid will dissolve until Q = K sp. ▫If Q > K sp, the salt will precipitate until Q = K sp.
Sample Calculation The K sp for BaSO 4 is 1.1 x 10¯ 10 and that for BaSeO 4 is 2.8 x 10¯ 11. A 1.0 M solution of BaCl 2 is added slowly to a solution that is 1.0 x 10¯ 4 M in sodium sulfate, Na 2 SO 4 and 1.0 x 10¯ 4 M in sodium selenate, Na 2 SeO 4. 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 BaCl 2 solution does not change the overall solution volume to any significant degree.)
Selective Precipitation of Ions One can use differences in solubilities of salts to separate ions in a mixture.
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/Selecti vePrecip.html