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4.5 Precipitation Reactions

4.5 Precipitation Reactions. Precipitation Reactions. When 2 solutions are mixed and an insoluble substance forms Precipitate - this insoluble substance To figure out what the solid is, we need to know what individual species are present in the solution after the mixture occurs. Example.

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4.5 Precipitation Reactions

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  1. 4.5 Precipitation Reactions

  2. Precipitation Reactions • When 2 solutions are mixed and an insoluble substance forms • Precipitate- this insoluble substance • To figure out what the solid is, we need to know what individual species are present in the solution after the mixture occurs

  3. Example We add potassium chromate and barium nitrate together and a yellow solid forms. What is it? • Write the reactants as they exist in solution. K2CrO4 (aq) + Ba(NO3)2(aq)  2K+(aq) + CrO42- (aq) + Ba2+(aq) + 2NO3-(aq) 

  4. Example • Find the possibilities for the solid. • Since K2CrO4 and Ba(NO3)2 are the beginning solutions, they cannot be the yellow solid. • The only other options are: KNO3 OR BaCrO4

  5. Example • Look at the solubility rules to figure out if either of these are soluble. • Since KNO3 is soluble, the solid must be: BaCrO4 • So equation must be: K2CrO4 (aq) + Ba(NO3)2(aq)  KNO3(aq) + BaCrO4(s)

  6. 4.6 Describing Reactions in Solution

  7. 3 Types of Equations • Molecular - overall reaction but not the actual species in solution • Complete Ionic – represents all strong electrolytes as ions • Net Ionic – Only species that undergo change are included, no spectators

  8. Example Aqueous potassium chloride is added to aqueous silver nitrate. Molecular Equation: • Check solubility rules to figure out what symbols to use after products. KCl(aq) + AgNO3(aq)  KNO3(aq) + AgCl(s)

  9. Example Complete Ionic Equation: • Break all strong electrolytes apart into ions • Leave solids, gases, liquids, and weak electrolytes alone. K+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq)  K+(aq) + NO3-(aq) + AgCl(s)

  10. Example Net Ionic Equation: • Cancel out all spectator ions: species that are identical on both sides of the equation • Must have same charges, states, formulas, etc. K+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq)  K+(aq) + NO3-(aq) + AgCl(s) Cl-(aq) + Ag+(aq)  AgCl(s)

  11. Example Sodium sulfate and lead (II) nitrate are mixed and a precipitate forms. Write the net ionic equation.

  12. Example • Identify species present Molecular Equation: Na2SO4(aq) + Pb(NO3)2(aq)  2NaNO3(aq) + PbSO4(s) Complete Ionic Equation: 2Na+(aq) + SO42-(aq) + Pb2+(aq) + 2NO3-(aq)  2Na+(aq) + 2NO3-(aq) + PbSO4(s)

  13. Example 2. Write balanced net ionic equation Spectator ions: sodium and nitrate 2Na+(aq) + SO42-(aq) + Pb2+(aq) + 2NO3-(aq)  2Na+(aq) + 2NO3-(aq) + PbSO4(s) Complete Ionic Equation: SO42-(aq) + Pb2+(aq)  PbSO4(s)

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