Solubility Equilibria. Even substances that are considered "insoluble" dissolve to a small extent.

Transcription

1 Solubility Equilibria Even substances that are considered "insoluble" dissolve to a small extent. When a solution contains the maximum amount of dissolved material, it is saturated. 1

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3 The undissolved solid and the few ions that dissolve are in equilibrium: AgI (s) Ag + (aq) + I (aq) Ksp = [Ag + ] [I ] Cu(OH)2 Cu +2 (aq) + 2OH (aq) Ksp = [Cu +2 ] [OH ] 2 Ca3(PO4)2 3Ca +2 (aq) + 2 PO4 3 (aq) Ksp = [Ca +2 ] 3 [PO4 3 ] 2 The equilibrium constant for this process is called the solubility product constant, Ksp. 3

4 Copper (I) bromide has a solubility of g/l. Calculate the solubility product constant, Ksp, for this compound. 4

5 In a saturated solution of Bi2S3, the [Bi +3 ] = 2.1x10 15 M. Calculate the Ksp for this compound. 5

6 salts 6

7 AgCl PbI2 7

8 CuCO3 Fe(OH)3 Ag2S 8

9 BaSO 4 9

10 Copper (II) Iodate has a Ksp value of 1.4x10 7. Calculate the concentration of the ions present in a saturated solution of copper (II) iodate and the solubility of the compound in g/100 ml. 10

11 Calculate the concentration of all ions in a saturated solution of Cr(OH)3 (Ksp = 6.7 x ) 11

12 The Common Ion Effect Salts are LESS soluble when common ions are present. LeChatlier's Principle: system will shift away from an addition CuS (s) Cu +2 (aq) + S 2 (aq) Add Cu(NO3)2 Add Na2S Both cause a shift left solubility decreases 12

13 What could be added to each of the following in order to decrease solubility? ZnCO3 Ag2CrO4 13

14 Calculate the molar solubility of CaF2 (Ksp = 4.0 x ) in a. Pure water b M NaF 14

15 ph and Solubility Some salts are less soluble at high (basic) ph. High ph has a larger [OH ], so this can be a common ion. Sn(OH)2 (s) Sn +2 (aq) + 2OH (aq) 15

16 Determine the molar solubility of Co(OH) 3 (K sp = 2.5 x ) in a solution that is buffered to a ph of

17 Low (acidic) ph can sometimes increase solubility If the anion is a strong conjugate base, it can react with acid in the solution. This removes the anion, causing the system to shift right, increasing solubility. Ag3PO4 (s) 3 Ag + (aq) + PO4 3 (aq) H + HPO4 2 System shifts right, and solubility increases. If the anion of the salt is a weak conjugate base, it will NOT react with acid, and there is no increase in solubility. AgCl (s) Ag + (aq) + Cl (aq) H + no reaction 17

18 Which of the following salts would show an increase in solubility in an acidic solution: CaSO4 AgOH CuS PbI2 Ba3(PO4)2 18

19 Another way to increase solubility: In addition to removing some of the anion, some of the cation can be removed, shifting the equilibrium to the right: the cation must be a transition metal a ligand must be added, forming a complex ion. PbCO3 (s) Pb +2 (aq) + CO3 2 (aq) NH3 Pb(NH3)4 +2 FeS (s) Fe +2 (aq) + S 2 (aq) SCN Fe(SCN)4 2 Equilibrium shifts right, and solubility increases 19

20 Predicting Precipitation Will a precipitate form when mixing two solutions? Calculate Qsp to find out! Qsp is calculated the same way as Ksp, only using original concentrations (not equilibrium). If Qsp < Ksp, then no precipitate will form If Qsp > Ksp, then a precipitate will form to find final concentrations after a precipitate forms, stoichiometry needs to be done first, then the equilibrium calculation. (Remember that stoichiometry is done in mmol, equilibrium in M) 20

21 150 ml of M AgNO3 is combined with 250 ml of M K2CrO4. Determine if a precipitate will form. (Ksp for Ag2CrO4 = 9.0 x ) If so, what is the [CrO4 2 ] after equilibrium is established. 21

22 250 ml of 0.95M AgNO3 is added to 150 ml of 0.45M K2SO4. a. Determine whether or not a precipitate forms (Ksp for Ag2SO4 = 1.2 x 10 5 ) Show calculations to support your answer. b. After the chemical reaction happens, determine the [ SO4 2 ] at equilibrium. c. A 1.0 liter saturated solution of Ag2SO4 is prepared. There is some solid left in the bottom of the beaker. 500 ml of water is added, and there is still some solid left in the beaker. After the addition, does the [Ag + ] increase, decrease, or remain the same? Explain. d. Some solid Na2SO4 is added to the above solution. Does the [Ag + ] increase, decrease, or remain the same? Explain. 22