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213 PHC

Precipitation Reactions and Titrations (1) 5 th lecture (1) Gary D. Christian, Analytical Chemistry, 6 th edition. 213 PHC. By the end of the lecture the student should be able to:. Understand the precipitation equilibria . Define the solubility product. Precipitation Equilibria.

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213 PHC

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  1. Precipitation Reactions and Titrations (1)5th lecture(1) Gary D. Christian, Analytical Chemistry, 6th edition. 213 PHC

  2. By the end of the lecture the student should be able to: • Understand the precipitation equilibria. • Define the solubility product.

  3. Precipitation Equilibria What is a precipitation reaction The ability of some compounds to form insoluble precipitates when reacted with certain reagents.

  4. Precipitation equilibria A very small amount of insoluble compounds dissolves in water forming a saturated solution. e.g. If solid AgCl is added to water, a small portion of it will dissolve: AgCl (AgCl)aq  Ag+ + Cl- An equilibrium is established between AgCl and its ions: K = [Ag+] [Cl-] / [AgCl]

  5. The Solubility product The product of the ions concentrations is constant at a given temperature. Ksp = [Ag+] [Cl-] This constant is called the solubility product constant. The solubility product of a substance equals the product of the molar conc. of the ions involved, each raised to a power equal to the no. of these ions.

  6. The Solubility product cont. A nonsymmetric salt such as Ag2CrO4 would have a Ksp as follows: Ag2CrO4 2 Ag+ + CrO42- Ksp = [Ag+]2 [CrO42-]

  7. Formation of the precipitate The precipitation will not take place unless the product of [Ag+] and [Cl-] exceeds the Ksp. If the product is just equal to Ksp all the Ag+ and Cl- remains in solution.

  8. Example 10.6 p. 327 • Example 10.8 p. 329 • Example 10.9 p. 329

  9. Questions?

  10. SUMMARY • Precipitation equilibria. • Solubility product. Thank you

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