Reactions in Aqueous Solution Chapter 4 – Part 2

Question What makes things work? Why do substances do what they do?

Precipitation Reactions Insoluble Solid Formation From the Mixing of Two Solutions

Precipitation Reactions When one mixes two solutions containing ions that form compounds that are insoluble, a precipitate is formed. Why do they do that?

Solubility Rules for Common Ionic Compounds In water at 250C Soluble Compounds Exceptions Compounds containing alkali metal ions and NH4+ None NO3-, HCO3-, ClO3- Cl-, Br-, I- Halides of Ag+, Hg22+, Pb2+ SO42- Sulfates of Ag+, Ca2+, Sr2+, Ba2+, Hg2+, Pb2+ Insoluble Compounds CO32-, PO43-, CrO42-, S2- OH- Compounds containing alkali metal ions and Ba2+ 4.2

AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq) Molecular Equation The molecular equation lists the reactants and products in their molecular form. AgNO3 (aq) + KCl (aq)  AgCl (s) + KNO3 (aq)

Ionic Equation In the ionic equation all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions. This more accurately reflects the species that are found in the reaction mixture. Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq)  AgCl (s) + K+ (aq) + NO3- (aq)

Writing Net Ionic Equations Write a balanced molecular equation. Dissociate all strong electrolytes. Cross out anything that remains unchanged from the left side to the right side of the equation. Write the net ionic equation with the species that remain.

Precipitation Reactions precipitate Pb(NO3)2 (aq) + 2NaI (aq) PbI2 (s) + 2NaNO3 (aq) molecular equation ionic equation net ionic equation ____________ are spectator ions 4.2

Gravimetric Analysis Dissolve unknown substance in water React unknown with known substance to form a precipitate Filter and dry precipitate Weigh precipitate Use chemical formula and mass of precipitate to determine amount of unknown ion 4.6

Electron Transfer Reactions Oxidation Reduction Electron Transfer Reactions

Oxidation-Reduction Reactions If a substance gives up electrons, something must have collided with that substance and accepted the electrons. Why do they do that?

Displacement Reactions In displacement reactions, ions oxidize or reduce an element. The ions, then, are reduced or oxidized.

Displacement Reactions In this reaction, silver ions oxidize copper metal. Cu (s) + 2 Ag+ (aq)  Cu2+ (aq) + 2 Ag (s)

Displacement Reactions The reverse reaction, however, does not occur. Cu2+ (aq) + 2 Ag (s)  Cu (s) + 2 Ag+ (aq) x

Activity Series

Oxidation-Reduction Reactions (electron transfer reactions) 2Mg (s) + O2 (g) 2MgO (s) Oxidation half-reaction (lose e-) Reduction half-reaction (gain e-) 4.4

Zn (s) + CuSO4 (aq) ZnSO4 (aq) + Cu (s) Agents Zn (s) + CuSO4 (aq) ZnSO4 (aq) + Cu (s) ___ is oxidized ___ is the reducing agent ____ is reduced ___ is the oxidizing agent 4.4

Copper wire reacts with silver nitrate to form silver metal. What is the oxidizing agent in the reaction? ___ is reduced ___ is the oxidizing agent 4.4

Oxidation Numbers To determine if an oxidation-reduction reaction has occurred, we assign an oxidation number to each element in a neutral compound or charged entity. Review the rules on calculating an oxidation number for atoms in a compound.

Types of Oxidation-Reduction Reactions Combination Reaction A + B C S + O2 SO2 Decomposition Reaction C A + B 2KClO3 2KCl + 3O2 4.4

Types of Oxidation-Reduction Reactions Displacement Reaction A + BC AC + B Sr + 2H2O Sr(OH)2 + H2 TiCl4 + 2Mg Ti + 2MgCl2 Cl2 + 2KBr 2KCl + Br2 4.4

Types of Oxidation-Reduction Reactions Disproportionation Reaction Element is simultaneously oxidized and reduced. Cl2 + 2OH- ClO- + Cl- + H2O 4.4

Ca2+ + CO32- CaCO3 NH3 + H+ NH4+ Zn + 2HCl ZnCl2 + H2 Ca + F2 CaF2 Classify the Following Reactions Ca2+ + CO32- CaCO3 NH3 + H+ NH4+ Zn + 2HCl ZnCl2 + H2 Ca + F2 CaF2 4.4

Balancing Equations That Cannot be Balanced by Inspection Oxidation Reduction Balancing Equations That Cannot be Balanced by Inspection

Balancing Redox Equations Break into Half Reactions Balance Half Reactions Balance all but H,O Balance O with water Balance H with H+ Balance charge with e- Add Half Reactions Together Practice Due 10/09/2006 11 AM