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Classes of Chemical Reactions Reactions in aqueous media • Precipitation reactions • Acid-Base reactions • Oxidation-Reduction reactions • Reversible reactions Classes of Chemical Reactions Water (H2O), a unique solvent most abundant liquid medium for biochemical reactions solvent of high polarity O H H + Classes of Chemical Reactions The solubility of ionic compounds: dissociation Cl- Na+ Cl- Cl- NaCl Na Na+ + ClNa+ O H H + Classes of Chemical Reactions O H H + Classes of Chemical Reactions electrolytes: a substance that conducts an electric current when dissolved in water Acids are donors of H+ (this is a definition) or HBr ! H3O+ + Br¯ HBr ! H+ + Br¯ O H H + Equations for Aqueous Ionic Reactions molecular equation: 2AgNO3 + Na2CrO4 ! Ag2CrO4(s) + 2NaNO3 total ionic equation: 2Ag+ + 2NO3¯ + 2Na+ + CrO42¯ ! Ag2CrO4(s) + 2Na+ + 2NO3¯ net ionic equation: 2Ag+ + CrO42¯ ! Ag2CrO4(s) Classes of Chemical Reactions Precipitation Reactions Driving Force for Precipitation Reactions: INSOLUBILITY Some ions combine to form insoluble products 2Al3+ + 3CO32¯ ! Al2(CO3)3 (s) No reaction in this case: KCl + NaBr: K+ + Cl- + Na+ + Br- ! same ions no precipitate Classes of Chemical Reactions Precipitation Reactions Table 4.1. Solubility Principles SOLUBLE INSOLUBLE 1. all common compounds of Group 1A ions and NH 4+ are soluble 1. all common metal hydroxides are insoluble, except alkali and alkaline earth 2. all common NO3 -, CH3CO2-, and ClO4are soluble 2. all common CO32- and PO43- are insoluble, except alkali and NH4+ 3. all halides, except Ag+, Pb2+, Cu+, and Hg22+ are soluble 3. all common sulfides (S2-) are insoluble, except alkali 4. all common SO42- are soluble, except Ca2+, Sr2+, Ba2+, and Pb2+ Classes of Chemical Reactions Acid-Base Reactions Acid - a substance that is a donor of H+: HX ! H+ + X¯ Base - a substance that is a donor of OH¯: MOH ! M+ + OH¯ Classes of Chemical Reactions Acid-Base Reactions STRONG ACIDS WEAK ACIDS Hydrochloric acid, HCl Hydrofluoric acid, HF Hydrobromic acid, HBr Phosphoric acid, H3PO4 Hydroiodic acid, HI Acetic acid, CH3CO2H Nitric acid, HNO3 Carbonic acid, H2CO3 Sulfuric acid, H2SO4 Perchloric acid, HClO4 Classes of Chemical Reactions Acid-Base Reactions STRONG BASES Sodium Hydroxide, NaOH Potassium Hydroxide, KOH WEAK BASES Ammonia, NH3 NH3 + H2O ! NH4+ + OH¯ Calcium Hydroxide, Ca(OH)2 Strontium Hydroxide, Sr(OH)2 Barium Hydroxide, Ba(OH)2 Cesium Hydroxide, CsOH Classes of Chemical Reactions Acid-Base Reactions Driving Force for Acid-Base Reactions: FORMATION OF WATER Ba2+ + 2OH¯ + 2H+ + 2Cl¯ ! Ba2+ + 2Cl¯ + 2H2O Classes of Chemical Reactions Acid-Base Reactions Driving Force for Acid-Base Reactions: FORMATION OF WATER Ba2+ + 2OH¯ + 2H+ + 2Cl¯ ! Ba2+ + 2Cl¯ + 2H2O Ba(OH)2 + 2HCl ! BaCl2 + 2H2O Classes of Chemical Reactions Acid-Base Reactions Driving Force for Acid-Base Reactions: FORMATION OF WATER Ba2+ + 2OH¯ + 2H+ + 2Cl¯ ! Ba2+ + 2Cl¯ + 2H2O Ba(OH)2 + 2HCl ! BaCl2 + 2H2O OH¯ + H+ ! H2O neutralization reaction Classes of Chemical Reactions Acid-Base Reactions Acid-Base Titrations: one solution of known concentration is used to determine the concentration of another solution HCl + NaOH ! NaCl + H2O Classes of Chemical Reactions Acid-Base Reactions Acid-Base Titrations: one solution of known concentration is used to determine the concentration of another solution HCl + NaOH ! NaCl + H2O Acid-Base Titrations Practice Problem 50.00 mL of an HCl solution of unknown concentration required 33.32 ml of 0.1524 M standard NaOH solution to reach the endpoint. What is the concentration of the HCl solution? Acid-Base Titrations Practice Problem 50.00 mL of an HCl solution of unknown concentration required 33.32 ml of 0.1524 M standard NaOH solution to reach the endpoint. What is the concentration of the HCl solution? HCl + NaOH ! NaCl + H2O Acid-Base Titrations Practice Problem 50.00 mL of an HCl solution of unknown concentration required 33.32 ml of 0.1524 M standard NaOH solution to reach the endpoint. What is the concentration of the HCl solution? HCl + NaOH ! NaCl + H2O n(HCl) = n(NaOH) = 0.03332 L " 0.1524 mol/L = 0.005078 mol Acid-Base Titrations Practice Problem 50.00 mL of an HCl solution of unknown concentration required 33.32 ml of 0.1524 M standard NaOH solution to reach the endpoint. What is the concentration of the HCl solution? HCl + NaOH ! NaCl + H2O n(HCl) = n(NaOH) = 0.03332 L " 0.1524 mol/L = 0.005078 mol 0.005078 mol 0.05000L = 0.1016 mol/L Oxidation-Reduction Red + Ox ! Products e– electrons reducing agent: loses electrons oxidizing agent: gains electrons Oxidation-Reduction Red + Ox ! Products e– electrons reducing agent: loses electrons oxidizing agent: gains electrons 2Mg + O2 ! 2MgO Mg2+ O2– Oxidation-Reduction Red + Ox ! Products e– electrons reducing agent: loses electrons oxidizing agent: gains electrons 2Mg + O2 ! 2MgO 4 electrons Mg2+ O2– Oxidation-Reduction Red + Ox ! Products e– electrons reducing agent: gets oxidized oxidizing agent: gets reduced 2Mg + O2 ! 2MgO 4 electrons Mg2+ O2– Oxidation-Reduction #$ Cl Cl + #+ H H non-polar covalent bond: electrons distributed evenly H Cl polar covalent bond: electrons distributed unevenly OXIDATION STATE: A MODEL, compounds treated as if electrons were transferred completely, not actually shared. +1 -1 H Cl Oxidation-Reduction redox reactions are characterized by change in oxidation state H2 + Cl2 ! 2HCl +1 -1 H Cl Oxidation-Reduction redox reactions are characterized by change in oxidation state H2 + Cl2 ! 2HCl reducing agent: loses electrons oxidizing agent: gains electrons +1 -1 H Cl Oxidation Number (State): General • For an atom in its elemental form equals 0 (H2, N2) • For monoatomic ion equals the ion charge (Ag+, S2-) • The sum of O.N. for the atoms in a compound is zero (HCl) • The sum of O.N. for the atoms in a polyatomic ion equals the ion charge ClO– +1 -2 Oxidation Number (State): General Rules for assigning an oxidation number 1. For Group 1A +1 in all compounds 2. For Group 2A +2 in all compounds 3. For hydrogen +1 in combination with nonmetals -1 in combination with metal and B 4. For fluorine -1 in all compounds 5. For oxygen -2 in all compounds except F and peroxides 6. For Group 7A (halogens) -1 except with O and halogens lower in the group Oxidants and Reducing Agents AgNO3 + NaCl ! AgCl(s) + NaNO3 Oxidants and Reducing Agents -2 +1 +1 -1 +1 -1 +1 -2 AgNO3 + NaCl ! AgCl(s) + NaNO3 +5 +5 Oxidants and Reducing Agents -2 +1 +1 -1 +1 -1 +1 -2 AgNO3 + NaCl ! AgCl(s) + NaNO3 +5 NOT a redox reaction +5 Oxidants and Reducing Agents -2 +1 +1 -1 +1 -1 +1 -2 AgNO3 + NaCl ! AgCl(s) + NaNO3 +5 +5 NOT a redox reaction 2Al + 3H2SO4 ! Al2(SO4)3 + 3H2 Oxidants and Reducing Agents -2 +1 +1 -1 +1 -1 +1 -2 AgNO3 + NaCl ! AgCl(s) + NaNO3 +5 +5 NOT a redox reaction 0 +1 -2 +3 -2 0 2Al + 3H2SO4 ! Al2(SO4)3 + 3H2 +6 +6 Oxidants and Reducing Agents -2 +1 +1 -1 +1 -1 +1 -2 AgNO3 + NaCl ! AgCl(s) + NaNO3 +5 +5 NOT a redox reaction 0 +1 -2 +3 -2 0 2Al + 3H2SO4 ! Al2(SO4)3 + 3H2 +6 +6 a redox reaction Balancing Redox Reactions K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O Balancing Redox Reactions K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O Step 1. Assign oxidation numbers Balancing Redox Reactions +1 +1 +1 +1 K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O Step 1. Assign oxidation numbers Balancing Redox Reactions +1 -2 +1 +1 +1 -2 K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O Step 1. Assign oxidation numbers Balancing Redox Reactions +1 -2 +1 +1 +1 -2 K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O -1 -1 Step 1. Assign oxidation numbers -1 0 Balancing Redox Reactions +1 -2 +1 +1 +3 +1 -2 K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O +6 -1 -1 -1 0 Step 1. Assign oxidation numbers Balancing Redox Reactions +1 -2 +1 +1 +3 +1 -2 K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O +6 -1 -1 -1 0 Step 1. Assign oxidation numbers Step 2. Find and the oxidant and reducing agent Balancing Redox Reactions +1 -2 +1 +1 +3 +1 -2 K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O +6 -1 -1 -1 0 Step 1. Assign oxidation numbers Step 2. Find and the oxidant and reducing agent Balancing Redox Reactions +1 -2 +1 +1 +3 +1 -2 K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O +6 -1 -1 -1 0 Step 1. Assign oxidation numbers Step 2. Find and the oxidant and reducing agent Balancing Redox Reactions +1 -2 +1 +1 +3 +1 -2 K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O +6 -1 -1 -1 0 Step 1. Assign oxidation numbers Step 2. Find and the oxidant and reducing agent Step 3. Determine the number of electrons: (a) gained by the oxidant Balancing Redox Reactions +1 -2 +1 +1 +3 +1 -2 K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O +6 -1 -1 -1 0 Step 1. Assign oxidation numbers Step 2. Find and the oxidant and reducing agent Step 3. Determine the number of electrons: (a) gained by the oxidant (3) Balancing Redox Reactions +1 -2 +1 +1 +3 +1 -2 K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O +6 -1 -1 -1 0 Step 1. Assign oxidation numbers Step 2. Find and the oxidant and reducing agent Step 3. Determine the number of electrons: (a) gained by the oxidant (3), and (b) lost by the reducing agent Balancing Redox Reactions +1 -2 +1 +1 +3 +1 -2 K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O +6 -1 -1 -1 0 Step 1. Assign oxidation numbers Step 2. Find and the oxidant and reducing agent Step 3. Determine the number of electrons: (a) gained by the oxidant (3), and (b) lost by the reducing agent (1) Balancing Redox Reactions +1 -2 +1 +1 +3 +1 -2 K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O +6 -1 -1 -1 0 Step 1. Assign oxidation numbers Step 2. Find and the oxidant and reducing agent Step 3. Determine the number of electrons: (a) gained by the oxidant (3), and (b) lost by the reducing agent (1) Step 4. (the key step) Assign coefficients to match the number of electrons lost and gained. Balancing Redox Reactions +1 -2 +1 +1 +3 +1 -2 K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O +6 -1 -1 -1 0 Step 1. Assign oxidation numbers Step 2. Find and the oxidant and reducing agent Step 3. Determine the number of electrons: (a) gained by the oxidant (3), and (b) lost by the reducing agent (1) Step 4. (the key step) Assign coefficients to match the number of electrons lost and gained. K2Cr2O7 + 6HI ! KI + CrI3 + 3I2 + H2O Balancing Redox Reactions +1 -2 +1 +1 +3 +1 -2 K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O +6 -1 -1 -1 0 Step 1. Assign oxidation numbers Step 2. Find and the oxidant and reducing agent Step 3. Determine the number of electrons: (a) gained by the oxidant (3), and (b) lost by the reducing agent (1) Step 4. (the key step) Assign coefficients to match the number of electrons lost and gained. Step 5. Complete balancing by inspection (by guessing) K2Cr2O7 + 6HI ! KI + CrI3 + 3I2 + H2O Balancing Redox Reactions +1 -2 +1 +1 +3 +1 -2 K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O +6 -1 -1 -1 0 Step 1. Assign oxidation numbers Step 2. Find and the oxidant and reducing agent Step 3. Determine the number of electrons: (a) gained by the oxidant (3), and (b) lost by the reducing agent (1) Step 4. (the key step) Assign coefficients to match the number of electrons lost and gained. Step 5. Complete balancing by inspection (by guessing) K2Cr2O7 + 6HI ! 2KI + 2CrI3 + 3I2 + 7H2O Balancing Redox Reactions +1 -2 +1 +1 +3 +1 -2 K2Cr2O7 + HI ! KI + CrI3 + I2 + H2O +6 -1 -1 -1 0 Step 1. Assign oxidation numbers Step 2. Find and the oxidant and reducing agent Step 3. Determine the number of electrons: (a) gained by the oxidant (3), and (b) lost by the reducing agent (1) Step 4. (the key step) Assign coefficients to match the number of electrons lost and gained. Step 5. Complete balancing by inspection (by guessing) K2Cr2O7 + 14HI ! 2KI + 2CrI3 + 3I2 + 7H2O READ SECTION 4.6: The activity series of the metals READ (!) SECTION 4.6: The activity series of the metals Reversible Reactions CaCO3 ! CaO + CO2 CaO + CO2 ! CaCO3 CaCO3 CaO + CO2 equilibrium system Practice Problem (4.70) Identify the oxidizing agent and the reducing agent in each of the following: 8H+ + 6Cl¯ + Sn + 4NO3¯ ! SnCl62¯ + 2NO2 + 4H2O Practice Problem (4.70) Identify the oxidizing agent and the reducing agent in each of the following: 8H+ + 6Cl¯ + Sn + 4NO3¯ ! SnCl62¯ + 2NO2 + 4H2O 2MnO4¯ + 10Cl¯ + 16H+ ! 5Cl2 + 2Mn2+ + 8H2O Practice Problem (4.75) Use the oxidation number method to balance the following equations by placing coefficients. Identifiy the reducing and oxidizing agents: (b) I2 + Na2S2O3 ! Na2S4O6 + NaI Practice Problem (4.83) Balance the following redox reaction and classify it as a combination, decomposition, or displacement reaction: (a) Ca + H2O ! Ca(OH)2 + H2 (b) NaNO3 ! NaNO2 + O2 (c) C2H2 + H2 ! C2H6