AP Chemistry Aqueous Equilibria II: Ksp & Solubility Products - PDF document

Slide 1 / 91 Slide 2 / 91 AP Chemistry Aqueous Equilibria II: Ksp & Solubility Products Slide 3 / 91 Table of Contents: K sp & Solubility Products Click on the topic to go to that section Introduction to Solubility Equilibria · Calculating K sp from the Solubility · Calculating Solubility from Ksp · Factors Affecting Solubility · Precipitation Reactions and Separation of Ions ·

Slide 4 / 91 Introduction to Solubility Equilibria Return to the Table of Contents Slide 5 / 91 Introduction to Solubility Equilibria Many shells are made of relatively insoluble calcium carbonate, so the shells are not at huge risk of dissolving in the ocean. Slide 6 / 91 Introduction to Solubility Equilibria Ionic compounds dissociate into their ions to different degrees when placed in water and reach equilibrium with the non-dissociated solid phase when the solution is saturated. Answer A saturated solution of CaCO 3 (s) Ca 2+ Ca 2+ CO 32- CO 32- CaCO 3 (s) Calcium carbonate is a relatively insoluble ionic salt. Would the picture look different for a soluble ionic salt such as Na 2 CO 3 ? Which solution would be the better electrolyte?

Slide 7 / 91 Introduction to Solubility Equilibria Consider the equilibrium that exists in a saturated solution of CaCO 3 in water: CaCO 3 (s) ↔ Ca 2+ (aq) + CO 32- (aq) Unlike acid-base equilibria which are homogenous, solubility equilibria are heterogeneous, there is always a solid in the reaction. Slide 8 / 91 Introduction to Solubility Equilibria The equilibrium constant expression for this equilibrium is K sp = [Ca 2+ ] [CO 32− ] where the equilibrium constant, K sp , is called the solubility product. There is never any denominator in K sp expressions because pure solids are not included in any equilibrium expressions. Slide 9 / 91 Solubility Equilibrium The degree to which an ionic compound dissociates in water can be determined by measuring it's "K sp " or solubility product equilibrium constant. CaCO 3 (s) --> Ca 2+ (aq) + CO 32- (aq) Ksp @ 25 C = 5.0 x 10 -9 Answer MgCO 3 (s) --> Mg 2+ (aq) + CO 32- (aq) Ksp @ 25 C = 6.8 x 10 -6 In both cases above, the equilibrium lies far to the left, meaning relatively few aqueous ions would be present in solution. Which saturated solution above would have the higher conductivity and why?

Slide 10 / 91 1 Which Ksp expression is correct for AgCl? [Ag + ]/[Cl - ] A [Ag + ][Cl - ] B [Ag 2+ ] 2 [Cl 2- ] 2 C [Ag + ] 2 [Cl - ] 2 D None of the above. E Slide 10 (Answer) / 91 1 Which Ksp expression is correct for AgCl? [Ag + ]/[Cl - ] B A Answer AgCl (s) # Ag +(aq) + Cl -(aq) [Ag + ][Cl - ] B Ksp = [Ag + ][Cl - ] [Ag 2+ ] 2 [Cl 2- ] 2 C [Ag + ] 2 [Cl - ] 2 D [This object is a pull None of the above. E tab] Slide 11 / 91 2 Given the reaction at equilibrium: Zn(OH) 2 (s) Zn 2+ (aq) + 2OH - (aq) what is the expression for the solubility product constant, K sp , for this reaction? K sp = [Zn 2+ ][OH - ] 2 / [Zn(OH) 2 ] A K sp = [Zn(OH) 2 ] / [Zn 2+ ][2OH - ] B K sp = [Zn 2+ ][2OH - ] C D K sp = [Zn 2+ ][OH - ] 2

Slide 11 (Answer) / 91 2 Given the reaction at equilibrium: Zn(OH) 2 (s) Zn 2+ (aq) + 2OH - (aq) what is the expression for the solubility product constant, K sp , for this reaction? Answer D K sp = [Zn 2+ ][OH - ] 2 K sp = [Zn 2+ ][OH - ] 2 / [Zn(OH) 2 ] A [This object is a pull tab] K sp = [Zn(OH) 2 ] / [Zn 2+ ][2OH - ] B K sp = [Zn 2+ ][2OH - ] C D K sp = [Zn 2+ ][OH - ] 2 Slide 12 / 91 3 Which Ksp expression is correct for Fe 3 (PO 4 ) 2 ? [Fe 2+ ] 3 [PO 43- ] 2 A [ Fe 2+ ] 3 /[ PO 43- ] 2 B [ Fe 3+ ] 2 [ PO 43- ] 2 C D [ Fe 2+ ] 2 /[ PO 43- ] 2 None of the above. E Slide 12 (Answer) / 91 3 Which Ksp expression is correct for Fe 3 (PO 4 ) 2 ? A [Fe 2+ ] 3 [PO 43- ] 2 A Answer B [ Fe 2+ ] 3 /[ PO 43- ] 2 Fe 3 (PO 4 ) 2(s) # 3 Fe 2+(aq) + 2PO 43-(aq) C [ Fe 3+ ] 2 [ PO 43- ] 2 Ksp = [Fe 2+ ] 3 [PO 43- ] 2 [ Fe 2+ ] 2 /[ PO 43- ] 2 D None of the above. E [This object is a pull tab]

Slide 13 / 91 4 When 30 grams of NaCl are mixed into 100 mL of distilled water all of the solid NaCl dissolves. The solution must be saturated and the K sp for the NaCl must be very high. True False Slide 13 (Answer) / 91 4 When 30 grams of NaCl are mixed into 100 mL of distilled water all of the solid NaCl dissolves. The solution must be saturated and the K sp for the NaCl must be very high. False The solution in this case is Answer unsaturated. It has the True capacity to dissolve more salt. False [This object is a pull tab] Slide 14 / 91 5 The conductivity of a saturated solution of Ag 2 CO 3 would be expected to be less than the conductivity of a saturated solution of CaCO 3 . Justify your answer. True False

Slide 14 (Answer) / 91 5 The conductivity of a saturated solution of Ag 2 CO 3 would be expected to be less than the conductivity of a saturated solution of CaCO 3 . Justify your answer. False True For solutions of the same Answer concentration, Ag 2 CO 3 would False dissociate into more ions so therefore it would have a greater conductivity [This object is a pull tab] Slide 15 / 91 Solubility The term solubility represents the maximum amount of solute that can be dissolved in a certain volume before any precipitate is observed. The solubility of a substance can be given in terms of grams per liter g/L or in terms of moles per liter mol/L The latter is sometimes referred to as molar solubility. For any slightly soluble salt the molar solubility always refers to the ion with the lower molar ratio. Slide 16 / 91 Solubility Example #1 Consider the slightly soluble compound barium oxalate, BaC 2 O 4 . The solubility of BaC 2 O 4 is 1.3 x 10 -3 mol/L. The ratio of cations to anions is 1:1. This means that 1.3 x 10 -3 moles of Ba 2+ can dissolve in one liter. Also, 1.3 x 10 -3 moles of C 2 O 42- can dissolve in one liter. What is the maximum amount (in grams) of BaC 2 O 4 that could dissolve in 2.5 L (before a solid precipitate or solid settlement occurs)?

Slide 17 / 91 Solubility Example #1 What is the maximum amount (in grams) of BaC 2 O 4 that could dissolve in 2.5 L (before a precipitate occurs)? The solubility of BaC 2 O 4 is 1.3 x 10 -3 mol/L. BaC 2 O 4 (s) --> Ba 2+ (aq) + C 2 O 42-(aq) 1.3 x 10 -3 mol BaC 2 O 4 3.25 x 10 - 3 g 2.5L x -------------------- = BaC 2 O 4 1 liter 3.25 x 10 - 3 g x 1 mole = 0.73g BaC 2 O 4 BaC 2 O 4 225.3 g 0.73g is the maximum amount of BaC 2 O 4 that could dissolve in 2.5 L before a precipitate forms. Slide 18 / 91 Solubility Example #2 Consider the slightly soluble compound lead chloride, PbCl 2 . The solubility of PbCl 2 is 0.016 mol/L. The ratio of cations to anions is 1:2. This means that 0.016 moles of Pb 2+ can dissolve in one liter. Twice as much, or 2(0.016) = 0.032 moles of Cl - can dissolve in one liter. Slide 19 / 91 Solubility Example #3 Consider the slightly soluble compound silver sulfate, Ag 2 SO 4 . The solubility of Ag 2 SO 4 is 0.015 mol/L. The ratio of cations to anions is 2:1. This means that 0.015 moles of SO 42- can dissolve in one liter. Twice as much, or 2(0.015) = 0.030 moles of Ag + can dissolve in one liter.

Slide 20 / 91 Solubility Remember that molar solubility refers to the ion with the lower mole ratio . It does not always refer to the cation, although in most cases it does. Molar Compound [Cation] [Anion] Solubility of Compound 1.3 x 10 -3 1.3 x 10 -3 1.3 x 10 -3 BaC 2 O 4 mol mol mol PbCl 2 0.016 mol/L 0.032 mol/L 0.016 mol/L Ag 2 SO 4 0.030 mol/L 0.015 mol/L 0.015 mol/L Slide 21 / 91 6 If the solubility of barium carbonate, BaCO 3 is 7.1 x 10 -5 M, this means that a maximum of _______barium ions, Ba 2+ ions can be dissolved per liter of solution. A 7.1 x 10 -5 moles B half of that C twice as much D one-third as much E one-fourth as much Slide 21 (Answer) / 91 6 If the solubility of barium carbonate, BaCO 3 is 7.1 x 10 -5 M, this means that a maximum of _______barium ions, Ba 2+ ions can be dissolved per liter of solution. A 7.1 x 10 -5 moles A Answer The ratio of ions is 1:1 the B half of that maximum amount of Ba 2+ is C twice as much 7.1 x 10 -5 moles per 1 liter. D one-third as much E one-fourth as much [This object is a pull tab]

Slide 22 / 91 If the solubility of barium carbonate, BaCO 3 is 7.1 x 10 -5 M, 7 this means that a maximum of _______carbonate ions, 2- ions can be dissolved per liter of solution. CO 3 A 7.1 x 10 -5 moles B half of that C twice as much D one-third as much E one-fourth as much Slide 22 (Answer) / 91 If the solubility of barium carbonate, BaCO 3 is 7.1 x 10 -5 M, 7 this means that a maximum of _______carbonate ions, 2- ions can be dissolved per liter of solution. CO 3 7.1 x 10 -5 moles A A B half of that Answer The ratio of ions is 1:1 the maximum amount of CO 32- is C twice as much 7.1 x 10 -5 moles per 1 liter. D one-third as much E one-fourth as much [This object is a pull tab] Slide 23 / 91 If the solubility of Ag 2 CrO 4 is 6.5 x 10 -5 M, this means 8 that a maximum of _______silver ions, Ag + , can be dissolved per liter of solution. A 6.5 x 10 -5 moles B twice 6.5 x 10 -5 moles C half 6.5 x 10 -5 moles D one-fourth 6.5 x 10 -5 moles E four times 6.5 x 10 -5 moles