notes ch 8 - CH302 Chapter 8 notes part 4 Common Ion...

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CH302 Chapter 8 notes part 4 Common Ion Effects Solubility Product Constants AgCl is not very soluble in water. A dynamic equilibrium exists between the ions in solution and those in the bulk solid ionic lattice. The reversible reaction and its equilibrium constant are: Ag S 2 Ag + S 2 +2 - HO 2 ⎯→ ⎯⎯ ←⎯ - 100% [ ] [ ] KA g S sp 2 2 == × +− 10 10 49 . ( ) ( ) Ca PO 3 Ca 2 PO 3 2+ 4 3 2s 2 4 3 100% 2 −+ + [ ] [ ] KC aP O sp 2 3 4 3 2 25 . × () ←+ + aq aq (s) Cl Ag AgCl K = [Ag + ] [Cl - ] =1 AgCl Note: Activity of a pure solid = 1, and now K is called K sp . For AgCl, K sp = [Ag + ] [Cl - ] = 1.8 x 10 -10 small, AgCl is not very soluble! The BIGGER K sp , the MORE SOLUBLE the species. Generically: X n Y m (s) nX m+ (aq) + mY n- (aq) so K sp = [Y n- ] m [X m+ ] n Consider the dissolution of silver sulfide in water. The solubility product expression for Ag 2 S is: The dissolution of solid calcium phosphate in water is represented as: The solubility product constant expression is: ( ) [] + + + + = + 3 4 4 2 sp 3 aq 4 1 aq 4 2 aq s 4 4 PO NH Ca K PO NH Ca PO CaNH Same rules apply for compounds with more than two kinds of ions. e.g., calcium ammonium phosphate. Molar solubility The maximum amount of the species that will dissolve at the temperature in question (often 25° C).
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notes ch 8 - CH302 Chapter 8 notes part 4 Common Ion...

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