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Chapter 18.3 Solubility Equilibria

Chapter 18.3 Solubility Equilibria. Dressen. Learning Objectives. Understand the dynamics of a dissolving substance. Be able to construct a K sp equlibrium expression (solubility product constant). Be able to calculate a Ksp value. Understand the common ion effect.

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Chapter 18.3 Solubility Equilibria

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  1. Chapter 18.3Solubility Equilibria Dressen

  2. Learning Objectives • Understand the dynamics of a dissolving substance. • Be able to construct a Kspequlibrium expression (solubility product constant). • Be able to calculate a Ksp value. • Understand the common ion effect.

  3. Review…Solubility Rules • Salts are generally more soluble in HOT water (Gases are more soluble in COLD water) • Alkali Metal salts are very soluble in water. NaCl, KOH, Li3PO4, Na2SO4 etc... • Ammonium salts are very soluble in water. NH4Br, (NH4)2CO3 etc… • Salts containing the nitrate ion, NO3-, are very soluble in water. • Most salts of Cl-, Br- and I- are very soluble in water - exceptions are salts containing Ag+ and Pb2+. soluble salts: FeCl2, AlBr3, MgI2 etc... “insoluble” salts: AgCl, PbBr2 etc...

  4. Dissolving a salt... • A salt is an ionic compound - usually a metal cation bonded to a non-metal anion. • The dissolving of a salt is an example of equilibrium. • The water molecules will start to pull out some of the ions from the salt crystal.

  5. At first, the only process occurring is the dissolving of the salt - the dissociation of the salt into its ions. • However, soon the ions floating in the water begin to collide with the salt crystal and are “pulled back in” to the salt. (precipitation) • Eventually the rate of dissociation is equal to the rate of precipitation. • The solution is now “saturated”. It has reached equilibrium.

  6. The equilibrium expression can be written …… But if we recognize that the amount of undissolved solid does not change, we can consider it is a constant. Therefore ….

  7. Animations Salt dissolving Molecular dynamics of salt dissolving

  8. Sample Problem What is the concentration of lead ions and chromate ions in saturated lead chromate solution at 25oC? (Ksp = 1.8 x 10-14)

  9. Common Ion Effect The lowering of solubility of an ionic compound as a result of the addition of a common ion is called the common ion effect. Common Ion Effect-Precipitation

  10. 18.3 Homework #37 Page 565 # 21, 22, 23, 24, 27, 28 Due Friday

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