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Chapter 16

Chapter 16. Applications of Equilibrium Principles 1.) In water: a precipitate and its ions AgCl(s) <--> Ag + (aq) + Cl - (aq). 16.2. Fig 16.2 page 427. Chapter 16. 2.) In water, a precipitate and a species used to dissolve it AgCl(s) + 2NH 3 (aq) <--> Ag(NH 3 ) 2 + (aq) + Cl -.

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Chapter 16

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  1. Chapter 16 • Applications of Equilibrium Principles • 1.) In water: a precipitate and its ions • AgCl(s) <--> Ag+(aq) + Cl-(aq)

  2. 16.2 Fig 16.2 page 427

  3. Chapter 16 • 2.) In water, a precipitate and a species used to dissolve it • AgCl(s) + 2NH3(aq) <--> Ag(NH3)2+(aq) + Cl-

  4. Solubility Equilibrium • Expression for Ksp: • Ex. AgCl • Ex. PbCl2

  5. Solubility Equilibrium • Uses for Ksp: • 1. Calculation of the concentration of one ion, knowing that of the other.

  6. Ksp Calculations Calculate [Pb2+] in a solution in equilibrium with lead chloride if [Cl-] = 0.200 M (see Table 16.1, p. 427). [Pb2+] = (1.7x10-5)/(2.0x10-1)2 = 0.00042 M.

  7. Solubility Equilibrium • Uses for Ksp: • 2. Determination of whether a precipitate will form. • P = ion product, (conc. given to you)

  8. Solubility Equilibrium • Uses for Ksp: • If P<Ksp, no precipitate has formed (equilibrium not established)

  9. Solubility Equilibrium • Uses for Ksp: • If P>Ksp, precipitate forms until P becomes equal to Ksp.

  10. Ksp Calculations • Suppose enough Ag+ is added to a solution 0.001 M of CrO42- to make [Ag+] = 0.001 M. Will silver chromate precipitate (Ksp Ag2CrO4 = 2 x 10-12)? • P= (orig. conc. Ag+)2 x (orig. conc. CrO42-) = (1x10-3)2 (1x10-3) = 1x10-9 > Ksp, precip. forms.

  11. Solubility Equilibrium • Uses for Ksp: • 3. Water solubility - What effects solubility? • What are unsaturated, saturated, & supersaturated solutions?

  12. Solubility Equilibrium • s = water solubility (often g/ 100 mL) • PbCl2(s) <--> Pb2+(aq) + 2Cl-(aq) • [Pb2+] = s, [Cl-] = 2s

  13. Ksp Calculations • The Ksp of lead (II) chloride at 25 degrees Celsius is given as 1.7 x 10-5. What is this compounds solubility, in grams per 100 ml, at this temperature? • 4s3 = Ksp = (1.7x10-5); s = 1.6x10-2 M; solubility = 0.44g/100mL.

  14. Dissolving Precipitates • 1.) strong acid (works with basic anions) - water insoluble metal hydroxides, virtually all carbonates, many sulfides. • Ex. CaCO3(s) + 2H+(aq) --> Ca2+(aq) + H2CO3(aq)

  15. Dissolving Precipitates • 2.) NH3 or OH- (works with cations that form complexes) - Ex. AgCl(s) + 2 NH3(aq) --> Ag(NH3)2+(aq) + Cl-(aq) • K = Ksp x Kf • See table 15.4, p. 416

  16. Dissolving Precipitates • Write a general expression for the Kf of : • Ag+(aq) + 2 NH3(aq) --> Ag(NH3)2+(aq)

  17. Ksp Calculations • Consider the previous reaction of silver chloride and ammonia. What is K for this reaction? Use K to determine the solubility (in mol/L) of AgCl in 1.00 M NH3. • K = Ksp x Kf = (1.8x10-10)(1.7x107) = 3.1 x 10-3; s2/1.00 = 3.1x10-3; s = 0.056 mol/L

  18. #49 p.441

  19. #50 before

  20. #50 after

  21. #51 #51 p.442

  22. #55 p.442 #55

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