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213 PHC

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

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213 PHC

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

  2. Precipitation Equilibria

  3. By the end of this lecture the student should be able to: Define precipitation reactions. Define the solubility product. Calculate the molar solubility.

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

  5. 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]

  6. 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.

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

  8. 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.

  9. Questions

  10. Summary Definition of precipitation reactions. Definition of the solubility product. Calculation of molar solubility.

  11. Thank you

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