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Ch. 16 Solubility and Complex Ion Equilibria

Ch. 16 Solubility and Complex Ion Equilibria. Ms. Pritchard. Bell Ringer. Even though PbI2 is not soluble (according to the solubility rules), does it dissociate in water?. Relative Solubilities. When comparing the relative solubilities of two salts, there are two situations

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Ch. 16 Solubility and Complex Ion Equilibria

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  1. Ch. 16 Solubility and Complex Ion Equilibria Ms. Pritchard

  2. Bell Ringer • Even though PbI2 is not soluble (according to the solubility rules), does it dissociate in water?

  3. Relative Solubilities • When comparing the relative solubilities of two salts, there are two situations • If the two (or more) salts dissolve to produce the same number of particles: Then we can directly compare the Ksp values: AgI(s) Ksp = 1.5x10-16 CuI(s) Ksp = 5.0x10-12 CaSO4(s) Ksp = 6.1x10-5 So we can rank the three salts’ solubility: CaSO4 > CuI > AgI

  4. Relative Solubilities • If the two (or more) salts dissolve to produce different numbers of particles: Then we have to find the solubilities of each salt and compare them: So we can rank the three salts’ solubility: Bi2S3 > Ag2S > CuS

  5. Determining Precipitation • We can determine if a salt will precipitate out by using the Ksp and calculating Q (just like in the equilibrium chapter) • When we compare the two, we can determine if the salt will stay in solution, or precipitate out • If Q is greater than Ksp, precipitation will occur until the concentrations are reduced to satisfy Ksp • If Q is less than Ksp, no precipitation will occur

  6. Example • A solution is prepared by adding 750.0mL of 4.00x10-3 M Ce(NO3)3 to 300mL of 2.00x10-2 M KIO3. Will Ce(IO3)3 (Ksp = 1.9x10-10) precipitate from this solution? • Write the balanced chemical equation • Calculate [Ce3+]0 and [IO3-]0 in the mixed solution

  7. Then calculate Q • Compare Q to Ksp Since Q is greater than Ksp, Ce(IO3)3 will precipitate from the mixed reaction

  8. Equilibrium Concentrations After Precipitation • Because it is not always used useful to just know if solid will precipitate, we sometimes need some additional information, such as the equilibrium concentrations of the ions in solution after precipitation.

  9. Selective Precipitation • When given a mixture of ions, we sometimes want to remove one of the metal ions. We can do this by selective precipitation. By using a reagent that reacts with one metal ion before the other, we can separate the mixture. • For example, say we have a mixture of Ba2+ and Ag+ ions. If we added NaCl, AgCl will precipitate (a white solid), and BaCl2 is soluble in water, so the Ba2+ will remain in solution.

  10. Complex Ions • A complex ion is a charged species that consists of a metal ion surrounded by ligands • A ligand is a Lewis base (something that has a lone electron pair that can be donated to an empty orbital on a metal ion to form a covalent bond) • For example, if you put Ag+ and NH3 in solution, it will form Ag(NH3)+ and will then form Ag(NH3)2+ • The formation of each of these compounds has an equilibrium constant, K1 and K2, called formation constants

  11. Homework • Pg. 767 #45, 48, 49, 51, 52, 57

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