17-1: Solubility Equilibria

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17-1 Solubility Equilibria
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Dissociation vs Dissolution

• Dissociation Separation of ions that occurs
  when an ionic compound dissolves (ions are
  produced)
• Dissolution process in which an ionic solid
  dissolves in a polar liquid
• Dissolution equation
  AgCl (s)
  ? Ag (aq) Cl- (aq)

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Precipitation

• The process in which ions leave a solution and
  regenerate an ionic solid
• Opposite of dissolution
• Precipitation equation
• Ag (aq) Cl- (aq) ? AgCl (s)
• Or
• AgCl (s) ? Ag (aq) Cl- (aq)

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Solubility Equilibria

• Occurs when dissolution and precipitation occur
  at the same rate
• AgCl (s) lt-- gt Ag (aq) Cl- (aq)

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Write the dissolution equations for

• NaCl
• NaCl (s) lt -- gt Na (aq) Cl- (aq)
• CaCl2
• CaCl2 (s) lt -- gt Ca2 (aq) 2 Cl- (aq)
• Ca3(PO4)2
• Ca3(PO4)2 (s) lt -- gt 3 Ca2 (aq)
  2 PO4-3 (aq)

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How does this compare to Keq?

• AgCl (s) lt-- gt Ag (aq) Cl- (aq)
• Keq AgCl-
• AgCl
• Change the Keq to Ksp called the solubility
  product constant
• Ksp is calculated from concentration of ions at
  equilibrium
• A small Ksp means that it is not very soluble

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In your book, pg. 567

• SP 2
• SP 3

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How does this tie in with real life?

• Caves form when limestone is dissolved by
  slightly acidic ground water. When carbon
  dioxide dissolves in water, it forms carbonic
  acid.
  CO2(g) H2O(l) ? H2CO3(aq)
• Had a cavity? Tooth enamel is made soluble by
  some foods. Fluoride in drinking water reduces
  the solubility.