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Chapter 21 Notes, part III

Chapter 21 Notes, part III. Ksp and Common Ion Effect. Solubility Product Constant. Salts have different solubilities; even salts we earlier considered insoluble have a very, very small amount of solubility in water.

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Chapter 21 Notes, part III

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  1. Chapter 21 Notes, part III Ksp and Common Ion Effect

  2. Solubility Product Constant • Salts have different solubilities; even salts we earlier considered insoluble have a very, very small amount of solubility in water. • The solubility product constant (Ksp) is an index of how soluble a salt is—the bigger the Ksp, the more soluble the salt is.

  3. Ksp • Ksp is based on Keq from Ch. 19; for example: • Keq for AgCl(s) D Ag+(aq) + Cl-(aq) would be: Keq = • But a solid is not dissolved, and thus does not have a constant, so: Ksp = [Ag+][Cl-] [Ag+][Cl-] [AgCl]

  4. Practice Problem #1 • What is the Ksp for Ag2SO4 if its solubility is 3.5x10-10M?

  5. Practice Problem #2 • What is the concentration of silver ions and chlorine ions in AgCl if Ksp=1.8x10-10 at 25oC?

  6. Practice Problem #3 • Calcium fluoride has Ksp=3.9x10-11. What is the concentration of fluoride ions?

  7. Practice Problem #4 • Ksp for Ag2S is 8x10-51. What is the concentration of Ag+ ions?

  8. Common Ion Effect • A common ion is an ion that two salts or a salt and an acid or base have in common. • The lowering of solubility of a substance by the addition of a common ion is called the common ion effect.

  9. Common Ion Effect • For example: • PbCrO4D Pb2+ + CrO42- Ksp=1.8x10-14 • If we add lead (II) nitrate (Pb(NO3)2), we are adding a common ion (see the dissociation reaction on the board).

  10. Common Ion Effect • Due to LeChatelier’s principle, the reaction will shift left because of the increased Pb2+ concentration, causing formation of PbCrO4 solid.

  11. Practice Problem #5 • Predict whether barium sulfate will precipitate if of 0.0010mol barium nitrate is mixed with 1.0L of 0.0040M sodium sulfate to form a 1.0L solution (Ksp of BaSO4 = 1.1x10-10)

  12. Practice Problem #6 • Predict whether silver cyanide will precipitate if 500mL of 0.00012M silver nitrate is mixed with 500mL of 0.00040M sodium cyanide to form a 1.0L solution (Ksp of AgCN=2.0x10-12)

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