Tang 02 b oxidation number method 2

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  • 1. BALANCING REDOX REACTIONS Oxidation Number Method
  • 2. OXIDATION NUMBER METHOD Redox reactions can be balanced using: a) Half Reactions b) Oxidation numbers Goal: To balance the electrons that are gained and lostNOTE: When half-reactions are not provided, and a reactiondoes not occur in either acidic or basic solution, then theoxidation number method can be used to balance a redoxreaction
  • 3. OXIDATION NUMBER METHOD Example #11. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) Al(s) + MnO2(s)  Al2O3(s) + Mn(s) 0 +4 -2 +3 -2 0
  • 4. OXIDATION NUMBER METHOD Example #11. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) +3 Al(s) + MnO2(s)  Al2O3(s) + Mn(s) 0 +4 -2 +3 -2 0 -4
  • 5. OXIDATION NUMBER METHOD Example #11. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) +3 Al(s) + MnO2(s)  Al2O3(s) + Mn(s) 0 +4 -2 +3 -2 0 -4 Ratio = 4:3 Each Al atom loses 3, .: 4 Al loses 12 Each Mn atom gains 4, .: 3 Mn gains 12
  • 6. OXIDATION NUMBER METHOD Example #11. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) +3 4 Al(s) + 3 MnO2(s)  Al2O3(s) + Mn(s) 0 +4 -2 +3 -2 0 -4 Ratio = 4:3
  • 7. OXIDATION NUMBER METHOD Example #11. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) +3 4 Al(s) + 3 MnO2(s)  2Al2O3(s) + 3Mn(s) 0 +4 -2 +3 -2 0 -4 Ratio = 4:3
  • 8. OXIDATION NUMBER METHOD Example #11. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) 4 Al(s) + 3 MnO2(s)  2Al2O3(s) + 3Mn(s)
  • 9. OXIDATION NUMBER METHOD Example #21. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) NH3(g) + O2(g)  NO2(g) + H2O(l) -3 +1 0 +4 -2 +1 -2
  • 10. OXIDATION NUMBER METHOD Example #21. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) +7 NH3(g) + O2(g)  NO2(g) + H2O(l) -3 +1 0 +4 -2 +1 -2 -2
  • 11. OXIDATION NUMBER METHOD Example #21. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) +7 NH3(g) + O2(g)  NO2(g) + H2O(l) -3 +1 0 +4 -2 +1 -2 -2 Ratio = 4:7 Each N atom loses 7, .: 4 N loses 28 Each O atom gains 2  each O2 gains 4, .: 7 O2 gains 28
  • 12. OXIDATION NUMBER METHOD Example #21. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) +7 4 NH3(g) + 7 O2(g)  NO2(g) + H2O(l) -3 +1 0 +4 -2 +1 -2 -2 Ratio = 4:7 Each N atom loses 7, .: 4 N loses 28 Each O atom gains 2  each O2 gains 4, .: 7 O2 gains 28
  • 13. OXIDATION NUMBER METHOD Example #21. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) +7 4 NH3(g) + 7 O2(g)  4 NO2(g) + 6H2O(l) -3 +1 0 +4 -2 +1 -2 -2 Ratio = 4:7 Each N atom loses 7, .: 4 N loses 28 Each O atom gains 2  each O2 gains 4, .: 7 O2 gains 28
  • 14. OXIDATION NUMBER METHOD Example #21. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) 4 NH3(g) + 7 O2(g)  4 NO2(g) + 6H2O(l)
  • 15. OXIDATION NUMBER METHOD Example #3: In acidic solution1. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) Cu(s) + NO3-(aq)  NO2(g) + Cu2+(aq) 0 +5 -2 +4 -2 +2
  • 16. OXIDATION NUMBER METHOD Example #3: In acidic solution1. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) +2 Cu(s) + NO3-(aq)  NO2(g) + Cu2+(aq) 0 +5 -2 +4 -2 +2 -1
  • 17. OXIDATION NUMBER METHOD Example #3: In acidic solution1. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) +2 Cu(s) + NO3-(aq)  NO2(g) + Cu2+(aq) 0 +5 -2 +4 -2 +2 -1 Ratio = 1:2 Each Cu atom gains 2, .: 1 Cu gains 2 Each N atom loses 1, .: 2 N loses 2
  • 18. OXIDATION NUMBER METHOD Example #3: In acidic solution1. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) +2 Cu(s) +2 NO3-(aq)  NO2(g) + Cu2+(aq) 0 +5 -2 +4 -2 +2 -1 Ratio = 1:2 Each Cu atom gains 2, .: 1 Cu gains 2 Each N atom loses 1, .: 2 N loses 2
  • 19. OXIDATION NUMBER METHOD Example #3: In acidic solution1. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) +2 Cu(s) +2 NO3-(aq)  2 NO2(g) + Cu2+(aq) 0 +5 -2 +4 -2 +2 -1 Ratio = 1:2 Each Cu atom gains 2, .: 1 Cu gains 2 Each N atom loses 1, .: 2 N loses 2
  • 20. OXIDATION NUMBER METHOD Example #3: In acidic solution1. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) 4H+ + Cu(s) +2 NO3-(aq)  2 NO2(g) + Cu2+(aq) + 2H2O 1. Write down the reactant and product and balance atoms other than oxygen and hydrogen. 2. Add H2O molecules to balance the oxygen atoms. 3. Add H+ ions to balance the hydrogen atoms. 4. Add electrons to balance the charge on both sides of the equation.
  • 21. OXIDATION NUMBER METHOD Example #3: In acidic solution1. Assign oxidation numbers to each element.2. Identify the increase and decrease in oxidation numbers.3. Determine the smallest whole-number ratio of the oxidized and reduced elements so that the total increase in oxidationnumbers equals the total decrease in oxidation numbers.4. Use the determined ratio from step 3 to balance the oxidized and reduced reactants.5. Balance the other elements/compounds by inspection.6. Add H2O, H+, and OH- as needed to balance reactions in acidic or basic solution (recall the half-reaction method rules) 4H+ + Cu(s) +2 NO3-(aq)  2 NO2(g) + Cu2+(aq) + 2H2O