Solubility Product Constant

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Solubility Product Constant

• H. Chemistry
• Mrs. Coyle

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Solubility Equilibrium

• AgCl(s) ? Ag (aq) Cl- (aq)
• The concentration of AgCl (s) is constant and
  AgCl is a strong electrolyte (dissociates almost
  completely), so
• Ksp Ag Cl-
• Ksp is the solubility product constant

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Example 1 (17) Calculate Ksp

• The concentration of Pb2 in a saturated
  solution of PbI2 is 1.3 x 10-3 M. What is its
  Ksp?
• Hint Write reaction. Set up equilibrium
  concentrations.
• Answer 8.8x10-9 M

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Example 2 (18) Calculate Solubility and
Concentration

• The Ksp of PbI2 at 25?C is 7.0 x 10-9.
• What is its molar solubility and the
• concentration of each ion at this
• temperature?
• AnswerPbI2 Pb21.2x10-3M
• I-2.4x10-3M

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Example 3(21) Predict Precipitation Using Q
(Ion Product)

• Will precipitation occur when 50.0 mL of
  3.00x10-2 M Pb(NO3)2 solution is added to 50 mL
  of 2.00x10-3 M KCl?
• The Ksp of PbCl2 1.62 x 10-5
• Strategy
• First find the new concentrations (total volume
  is 100mL). Use M1V1 M2V2
• Calculate the Q (Ion Product similar to reaction
  quotient).
• Compare Q to Ksp. If Q gt Ksp precipitation will
  occur until QKsp.
• Answer Q1.5x10-8ltKsp , so no precipitation.

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Example 4( 23) Selective Precipitation

• If a solution contains 1.00x 10-2 M Cl- and
  1.00 x 10-3M I-, which will precipitate first
  AgCl or AgI, if AgNO3 is added a drop at a time
  (assume no volume change).
• Ksp AgCl 1.81 x 10-10 AgI 8.32
  x 10-17
• Strategy Using the Ksp, calculate the highest
  concentration of Ag that would not cause
  precipitation. The reagent that would require the
  lower concentration of Ag to cause
  precipitation, will precipitate first.

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Example 4( 23) Selective Precipitation

• Answer
• Ag 1.81x10-8M in AgCl
• Ag 8.32x10-14M in AgI
• AgI will precipitate first.
• Less concentration of Ag is required to
• cause precipitation.