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 Slide 4 / 91 Table of Contents: K sp & Solubility Products Click on the topic to go to that section Introduction to Introduction to Solubility Equilibria · Calculating K sp from the Solubility Solubility Equilibria · Calculating Solubility from Ksp · Factors Affecting Solubility · Return to the Precipitation Reactions and Separation of Ions · Table of Contents Slide 5 / 91 Slide 6 / 91 Introduction to Solubility Equilibria 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- Many shells are made of relatively insoluble calcium carbonate, so CaCO 3 (s) the shells are not at huge risk of dissolving in the ocean. 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 Slide 8 / 91 Introduction to Solubility Equilibria Introduction to Solubility Equilibria Consider the equilibrium that exists in a saturated solution of CaCO 3 in water: The equilibrium constant expression for this equilibrium is CaCO 3 (s) ↔ Ca 2+ (aq) + CO 32- (aq) K sp = [Ca 2+ ] [CO 32− ] where the equilibrium constant, K sp , is called the Unlike acid-base equilibria which are homogenous, solubility product. solubility equilibria are heterogeneous, there is always a solid in the reaction. There is never any denominator in K sp expressions because pure solids are not included in any equilibrium expressions. Slide 9 / 91 Slide 10 / 91 Solubility Equilibrium 1 Which Ksp expression is correct for AgCl? [Ag + ]/[Cl - ] The degree to which an ionic compound dissociates in water can be A determined by measuring it's "K sp " or solubility product equilibrium [Ag + ][Cl - ] B constant. [Ag 2+ ] 2 [Cl 2- ] 2 C CaCO 3 (s) --> Ca 2+ (aq) + CO 32- (aq) Ksp @ 25 C = 5.0 x 10 -9 [Ag + ] 2 [Cl - ] 2 Answer D MgCO 3 (s) --> Mg 2+ (aq) + CO 32- (aq) Ksp @ 25 C = 6.8 x 10 -6 None of the above. E 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 (Answer) / 91 Slide 11 / 91 1 Which Ksp expression is correct for AgCl? 2 Given the reaction at equilibrium: Zn(OH) 2 (s) Zn 2+ (aq) + 2OH - (aq) [Ag + ]/[Cl - ] what is the expression for the solubility product B A constant, K sp , for this reaction? Answer AgCl (s) # Ag +(aq) + Cl -(aq) [Ag + ][Cl - ] B Ksp = [Ag + ][Cl - ] [Ag 2+ ] 2 [Cl 2- ] 2 C K sp = [Zn 2+ ][OH - ] 2 / [Zn(OH) 2 ] [Ag + ] 2 [Cl - ] 2 A D [This object is a pull None of the above. E tab] K sp = [Zn(OH) 2 ] / [Zn 2+ ][2OH - ] B K sp = [Zn 2+ ][2OH - ] C K sp = [Zn 2+ ][OH - ] 2 D

Slide 11 (Answer) / 91 Slide 12 / 91 2 Given the reaction at equilibrium: 3 Which Ksp expression is correct for Fe 3 (PO 4 ) 2 ? Zn(OH) 2 (s) Zn 2+ (aq) + 2OH - (aq) what is the expression for the solubility product [Fe 2+ ] 3 [PO 43- ] 2 A constant, K sp , for this reaction? Answer D [ Fe 2+ ] 3 /[ PO 43- ] 2 B K sp = [Zn 2+ ][OH - ] 2 [ Fe 3+ ] 2 [ PO 43- ] 2 C K sp = [Zn 2+ ][OH - ] 2 / [Zn(OH) 2 ] A D [ Fe 2+ ] 2 /[ PO 43- ] 2 [This object is a pull tab] None of the above. K sp = [Zn(OH) 2 ] / [Zn 2+ ][2OH - ] E B K sp = [Zn 2+ ][2OH - ] C K sp = [Zn 2+ ][OH - ] 2 D Slide 12 (Answer) / 91 Slide 13 / 91 4 When 30 grams of NaCl are mixed into 100 mL of 3 Which Ksp expression is correct for Fe 3 (PO 4 ) 2 ? distilled water all of the solid NaCl dissolves. The solution must be saturated and the K sp for the NaCl must be very A [Fe 2+ ] 3 [PO 43- ] 2 high. A Answer [ Fe 2+ ] 3 /[ PO 43- ] 2 B Fe 3 (PO 4 ) 2(s) # 3 Fe 2+(aq) + 2PO 43-(aq) [ Fe 3+ ] 2 [ PO 43- ] 2 C Ksp = [Fe 2+ ] 3 [PO 43- ] 2 True [ Fe 2+ ] 2 /[ PO 43- ] 2 D False None of the above. E [This object is a pull tab] Slide 13 (Answer) / 91 Slide 14 / 91 4 When 30 grams of NaCl are mixed into 100 mL of 5 The conductivity of a saturated solution of Ag 2 CO 3 would distilled water all of the solid NaCl dissolves. The solution be expected to be less than the conductivity of a must be saturated and the K sp for the NaCl must be very saturated solution of CaCO 3 . Justify your answer. high. False The solution in this case is True Answer unsaturated. It has the True capacity to dissolve more False salt. False [This object is a pull tab]

Slide 14 (Answer) / 91 Slide 15 / 91 5 The conductivity of a saturated solution of Ag 2 CO 3 would Solubility be expected to be less than the conductivity of a saturated solution of CaCO 3 . Justify your answer. The term solubility represents the maximum amount of solute that can be dissolved in a certain volume before any precipitate is False observed. True For solutions of the same Answer concentration, Ag 2 CO 3 would The solubility of a substance can be given in terms of dissociate into more ions so False therefore it would have a greater grams per liter g/L conductivity or in terms of [This object is a pull tab] 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 Slide 17 / 91 Solubility Solubility Example #1 Example #1 What is the maximum amount (in grams) of BaC 2 O 4 that could Consider the slightly soluble compound barium oxalate, dissolve in 2.5 L (before a precipitate occurs)? BaC 2 O 4 . The solubility of BaC 2 O 4 is 1.3 x 10 -3 mol/L. 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 The ratio of cations to anions is 1:1. 2.5L x -------------------- = BaC 2 O 4 1 liter This means that 1.3 x 10 -3 moles of Ba 2+ can dissolve in one liter. 3.25 x 10 - 3 g x 1 mole = 0.73g BaC 2 O 4 Also, 1.3 x 10 -3 moles of C 2 O 42- can dissolve in one liter. BaC 2 O 4 225.3 g 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 0.73g is the maximum amount of BaC 2 O 4 that could dissolve occurs)? in 2.5 L before a precipitate forms. Slide 18 / 91 Slide 19 / 91 Solubility Solubility Example #2 Example #3 Consider the slightly soluble compound lead chloride, Consider the slightly soluble compound silver sulfate, PbCl 2 . Ag 2 SO 4 . The solubility of PbCl 2 is 0.016 mol/L. The solubility of Ag 2 SO 4 is 0.015 mol/L. The ratio of cations to anions is 1:2. The ratio of cations to anions is 2:1. This means that 0.016 moles of Pb 2+ can dissolve This means that 0.015 moles of SO 42- can dissolve in one liter. in one liter. Twice as much, or 2(0.016) = 0.032 moles of Cl - can Twice as much, or 2(0.015) = 0.030 moles of Ag + can dissolve in one liter. dissolve in one liter.

Slide 20 / 91 Slide 21 / 91 Solubility 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+ Remember that molar solubility refers to the ion with ions can be dissolved per liter of solution. the lower mole ratio . It does not always refer to the cation, although in most cases it does. A 7.1 x 10 -5 moles Molar B half of that Compound Solubility of [Cation] [Anion] C twice as much Compound 1.3 x 10 -3 1.3 x 10 -3 1.3 x 10 -3 D one-third as much BaC 2 O 4 mol mol mol E one-fourth as much 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 (Answer) / 91 Slide 22 / 91 If the solubility of barium carbonate, BaCO 3 is 7.1 x 10 -5 M, 6 If the solubility of barium carbonate, BaCO 3 is 7.1 x 10 -5 M, 7 this means that a maximum of _______carbonate ions, this means that a maximum of _______barium ions, Ba 2+ 2- ions can be dissolved per liter of solution. CO 3 ions can be dissolved per liter of solution. A 7.1 x 10 -5 moles A A 7.1 x 10 -5 moles Answer B half of that The ratio of ions is 1:1 the B half of that maximum amount of Ba 2+ is C twice as much C twice as much 7.1 x 10 -5 moles per 1 liter. D one-third as much D one-third as much E one-fourth as much [This object is a pull E one-fourth as much tab] Slide 22 (Answer) / 91 Slide 23 / 91 If the solubility of barium carbonate, BaCO 3 is 7.1 x 10 -5 M, If the solubility of Ag 2 CrO 4 is 6.5 x 10 -5 M, this means 7 this means that a maximum of _______carbonate ions, 8 that a maximum of _______silver ions, Ag + , can be 2- ions can be dissolved per liter of solution. CO 3 dissolved per liter of solution. A 6.5 x 10 -5 moles A 7.1 x 10 -5 moles A B twice 6.5 x 10 -5 moles B half of that Answer The ratio of ions is 1:1 the maximum amount of CO 32- is C half 6.5 x 10 -5 moles C twice as much 7.1 x 10 -5 moles per 1 liter. D one-fourth 6.5 x 10 -5 moles D one-third as much E four times 6.5 x 10 -5 moles E one-fourth as much [This object is a pull tab]