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CHAPTER 17 - SOLUBILITY AND PRECIPITATION

CHAPTER 17 - SOLUBILITY AND PRECIPITATION. Read intro on page 560 Dissolution CaCl 2(s) ↔ Ca +2 (aq) + 2 Cl - (aq) Precipitation Ca +2 (aq) + 2 Cl - (aq) ↔ CaCl 2(s) K sp = [ Ca +2 ] [ Cl - ] 2. Students complete practice problems 1 & 2 on page 565

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CHAPTER 17 - SOLUBILITY AND PRECIPITATION

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  1. CHAPTER 17 - SOLUBILITY AND PRECIPITATION

  2. Read intro on page 560 • Dissolution CaCl2(s)↔ Ca+2(aq) + 2 Cl-(aq) • Precipitation Ca+2(aq) + 2 Cl-(aq)↔ CaCl2(s) • Ksp = [Ca+2] [Cl-]2

  3. 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.

  4. 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

  5. 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).

  6. If Q = Ksp the solution is at equilibrium. • If Q > Ksp the solution is supersaturated and a precipitate will form. • If Q < Ksp the solution is unsaturated. • Chemical reactions that result in a precipitate form a product that has a Q greater than the precipitate’s Ksp.

  7. 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.

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

  9. 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

  10. The common-ion effect • This is a shift in the equilibrium because the concentration of one of the equilibrium ions is changed. (Le Chatelier’s Principle) • CaSO4(s)↔ Ca+2(aq) + SO4-2(aq) • What will happen if Na2SO4 is added? • Will shift to the left • More CaSO4 will precipitate out.

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