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Chapter 4: Chemical Quantities & Aqueous Reactions

Chapter 4: Chemical Quantities & Aqueous Reactions. CHE 123: General Chemistry I Dr. Jerome Williams, Ph.D. Saint Leo University. Overview. Precipitation 101 Expressing Precipitation Reactions. Precipitation 101.

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Chapter 4: Chemical Quantities & Aqueous Reactions

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  1. Chapter 4: Chemical Quantities & Aqueous Reactions CHE 123: General Chemistry I Dr. Jerome Williams, Ph.D. Saint Leo University

  2. Overview • Precipitation 101 • Expressing Precipitation Reactions

  3. Precipitation 101 • A precipitate is an insoluble solid; the supernatant liquid is the portion found above the settled precipitate. • We use solubility rules as a separation tool (remove a component from a mixture).

  4. Precipitation 101 • So far, we can predict the solubility of: (a) CdCO3(b) MgO (c) Na2S (d) PbSO4(e) (NH4)3PO4(f) HgCl2

  5. Precipitation 101 • Now predict whether a precipitate will form for: • (a) NiCl2(aq) + (NH4)2S(aq)  • (b) Na2CrO4(aq) + Pb(NO3)2(aq) • (c) AgClO4(aq) + CaBr2(aq)

  6. Precipitation 101 • How do we predict products? • The Beaker Analogy • 1. Draw beaker • 2. Place ions into beaker • 3. Identify candidates • 4. Write out products (identify precipitate)

  7. Expressing Precipitation Reactions • Three basic equations seen for precipitation reactions: • Molecular Equation: All reactants and products are written in molecular form. • Ionic Equation: All dissolved strong electrolytes are written as the dissociated ions. • Net Ionic Equation: All ions that are identical on both sides are deleted.

  8. Expressing Precipitation Reactions • Molecular Equation: All reactants and products are written in molecular (non-dissociated) form along with their phases. • Pb(NO3)2(aq) + 2 KCl(aq) PbCl2(s) + 2 KNO3(aq) • 2 HCl(aq) + Cu(OH)2(s)  CuCl2(aq) + 2 HOH(l) • C2H3O2H(aq) + KOH(aq)  KC2H3O2(aq) + HOH(l)

  9. Expressing Precipitation Reactions • Ionic Equation: All dissolved strong electrolytes in the molecular equation are broken into their ions. • Pb2+ + 2 NO3– + 2 K+ + 2 Cl– PbCl2(s) + 2 K+ + 2 NO3– • 2 H+ + 2 Cl– + Cu(OH)2(s)  Cu2+ + 2 Cl– + 2 HOH(l) • C2H3O2H(aq) + K+ + OH–  K+ + C2H3O2– + HOH(l)

  10. Expressing Precipitation Reactions • Net Ionic Equation:Spectator ions that occur on both sides are cancelled to give only those species which undergo change. • Pb2+ + 2 Cl– PbCl2(s) • 2 H+ + Cu(OH)2(s)  Cu2+ + 2 HOH(l) • C2H3O2H(aq) + OH–  C2H3O2– + HOH(l)

  11. Expressing Precipitation Reactions • Write the molecular, complete ionic equation, and net ionic equations for the following reactions: • AgNO3(aq) + Na2CrO4(aq)  • K2SO4(aq) + MgCO3(aq) 

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