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(7.6)

(7.6). Solubility Product Constant (K sp ). The Terms. Solubility : - a measure of the ability of a substance to dissolve Saturated Solution : - has the maximum amount of solute dissolved in a given volume of solvent at a given temperature Unsaturated :

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(7.6)

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  1. (7.6) Solubility Product Constant (Ksp)

  2. The Terms Solubility: - a measure of the ability of a substance to dissolve Saturated Solution: - has the maximum amount of solute dissolved in a given volume of solvent at a given temperature Unsaturated: - has less than the maximum… Supersaturated: - has more than the maximum…

  3. The Terms Solubility: - measured in g of solute per 100 mL of solution units: (g/100 mL) Molar Solubility: - measured in mole of solute per litre of solution units: (mol/L)

  4. Solubility Product Constant • Background: • For saturated solutions at equilibrium we use the solubility product constant • Symbolized by Ksp • Ksp is similar to K (units are mol/L) • Ksp deals with ions instead of gases • One side of the eq’n has a solid (which is ignored) • Refers to a solid dissolving in water

  5. Solubility Product Constant Ex: Zn(OH)2(s) ↔ Zn2+(aq) + 2 OH1-(aq) • Since Ksp is always calculated by just multiplying concentrations, it is called a “solubility product” constant - Ksp.

  6. Solubility Product Constant Ex: Zn(OH)2(s) ↔ Zn2+(aq) + 2 OH1-(aq) • Note: Notice that Zn(OH)2(s) is left out of the expression! Why? • Physical states matter when you are writing the eqm law equation! • See p484/p802 for values of Ksp

  7. Solubility Product Constant (Ksp) Note- • Used for saturated solutions. • Used for ionic compounds of low solubility, because under ordinary conditions highly soluble ionic compounds do not form precipitates. Their solutions, as used, are not saturated, no solubility equilibrium is established. • Units are omitted from values. • The lower the value of Ksp the lower the solubility of the compound.

  8. Solubility Conversions? • Solubility of MgF2 = 1.72 ×10-3 g/100mL What is its molar solubility (mol/L)? • Molar solubility of ZnCO3 = 3.87 ×10-6 mol/L What is its solubility (in g/100mL)?

  9. Sample Problems • These problems are similar to K except used for solubility.

  10. Sample Problems 1. A chemist finds that the molar solubility of silver carbonate, Ag2CO3, is 1.3 x 10-4 mol/L at 25C. Calculate Ksp for silver carbonate. (Ans: 8.8 x 10-12 )

  11. Sample Problems 2. A saturated solution of copper(II) phosphate, Cu3(PO4)2, has a solubility of 6.1 x 10-7 g/100 mL of solution at 25C. What is the Ksp for copper(II) phosphate at 25C? (Ans:1.1 x 10-37) 3. The Ksp for lead(II) iodide, PbI2 , at room temperature is 9.8 x 10-9. What is the molar solubility of PbI2 at room temperature? (Ans:1.3 x 10-3 mol/L)

  12. Will a Precipitate Form? Use trial ion product, Qsp, and compare the value to Ksp. • If Qsp < Ksp • rxn is not at eqm • soln is unsaturated, ppt is not present • If Qsp > Ksp • rxn is not at eqm • soln is supersaturated, ppt is present • If Qsp = Ksp • rxn is at eqm • soln is saturated, ppt is not present

  13. Sample Problems 4. Consider an aqueous solution containing Ag1+ and Cl1- ions, each at a concentration of 1.0 x 10-5 mol/L. Will precipitation occur? (ans: Qsp < Ksp , no ppt forms) 5. A chemist mixes 100.0 mL of 0.25 mol/L Pb(NO3) 2 with 200.0 mL of 0.070 mol/L NaBr. a) Write the balanced chemical equation for the reaction. b) Does a precipitate form? Hint: Recall dilution. (ans: Qsp > Ksp , ppt forms)

  14. Homework Text • p 486 #1-4 • p 489 #5, 6 • p 493 #1, 3-10 TEST Chapter 7 FRIDAY

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