CHAPTER 17 SOLUBILITY AND PRECIPITATION

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CHAPTER 17 - SOLUBILITY AND PRECIPITATION
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• Read intro on page 560
• Dissolution
• CaCl2(s) ? Ca2(aq) 2 Cl-(aq)
• Precipitation
• Ca2(aq) 2 Cl-(aq) ? CaCl2(s)
• Ksp Ca2 Cl-2

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• Students complete practice problems 1 2 on
  page 565
• We can look up the solubility product constant
  of many materials at 25 oC.
  (see page 566).
• Demonstrate problem 2 on page 567
• Students complete problems 3 4 on page
  567.

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USING KSP TO CALCULATE ION CONCENTRATIONS

• Review writing ionic equations (worksheet).
• Students earmark polyatomic ion page in notes (or
  ask on a test).
• Complete sample problem 3.
• Students complete practice problems 5 6

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PREDICTING THE FORMATION OF A PRECIPITATE

• Insert the ion concentrations into the Ksp
  equation and calculate the Ksp.
• Since we do not know if the solution is at
  equilibrium, we call the Ksp the ion product
  quotient (Q) (same as the reaction product
  quotient).

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• If Q Ksp the solution is at equilibrium.
• If Q gt Ksp the solution is supersaturated and a
  precipitate will form.
• If Q lt Ksp the solution is unsaturated.
• Chemical reactions that result in a
  precipitate form a product that has a Q greater
  than the precipitates Ksp.

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Can also predict a precipitate rather than
calculate

• The rules on page 574 can be used to predict
  a precipitate.
• A double replacement reaction will take
  place if an insoluble (or slightly
  soluble) compound is formed.
• AgNO3(aq)KBr(aq) ?AgBr(s)KNO3(aq)
• A double replacement reaction will also take
  place if water or a gas is formed.

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• Demonstrate sample problem 4
• Assign practice problems 7 8.

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Net ionic equation

• A net ionic equation includes only the change.
• Total equation
• AgNO3(aq) KBr(aq) ? AgBr(s) KNO3(aq)
• Net Ionic Equation
• Ag(aq) Br-(aq) ? AgBr(s)
• NO3- and K are called spectator ions because
  they do not participate in the reaction

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The common-ion effect

• This is a shift in the equilibrium because the
  concentration of one of the equilibrium ions
  is changed. (Le Chateliers Principle)
• CaSO4(s)? Ca2(aq) SO4-2(aq)
• What will happen if Na2SO4 is added?
• Will shift to the left
• More CaSO4 will precipitate out.