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Oxidation – Reduction (Redox)

Oxidation – Reduction (Redox). I. Redox. Assigning oxidation numbers Use the periodic chart! O -2 Oxidation Number is -2 K +1 Oxidation Number is +1 Fe Oxidation Number is 0. 11e -. 11p +. Na atom. Oxidation – Loss of Electrons. Iron Rusting: Fe  Fe 3+ + 3 e -

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Oxidation – Reduction (Redox)

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  1. Oxidation – Reduction (Redox)

  2. I. Redox • Assigning oxidation numbers • Use the periodic chart! • O-2 • Oxidation Number is -2 • K+1 • Oxidation Number is +1 • Fe • Oxidation Number is 0

  3. 11e- 11p+ Na atom Oxidation – Loss of Electrons • Iron Rusting: • Fe  Fe 3+ + 3 e- • S-2 S + 2 e- 10e- 11p+ 1e- lose 1 electron Na+1ion Electrons on right side of arrow

  4. 18e- 17p+ Reduction – Gain of electrons • Cu+2 + 2 e- Cu • S + 2 e- S-2 17e- 17p+ +1e- gain 1 electron Cl-ion Cl atom Electrons on left side of arrow

  5. Mnemonic device • “LEO the lion says GER!” • LEO = Loss of Electrons is OXIDATION • GER = Gain of Electrons is REDUCTION

  6. Oxidizing agent – the species that causes oxidation the species that is reduced (gains electrons) • Reducing agent – the species that causes reduction the species that is oxidized (loses electrons)

  7. Tin (II) chloride is added to Solid Aluminum 3 Sn + AlCl3 3 2 2 +2 -1 0 0 +3 -1 Al Sn SnCl2 Al  a) Write the balanced equation: SnCl2 + Al b) Assign oxidation numbers to all elements c) Which species is oxidized?__________ Which species is reduced? ___________  d) What is the oxidizing agent?___________ What is the reducing agent? __________

  8. Hydrochloric Acid added to Aluminum  a) Write the balanced equation: HCl + Al b) Assign oxidation numbers to all elements c) Which species is oxidized?__________ Which species is reduced? ___________  d) What is the oxidizing agent?___________ What is the reducing agent? __________ 3 H2 + AlCl3 2 6 2 +1 -1 0 0 +3 -1 Al H HCl Al

  9. II. Writing half-reaction A. Recall: Subatomic particles 29 29 29 29 29 27 Why are electrons lost/gained rather than protons?

  10. B. Oxidation half reactions: LEO Cu0 Cu+2 + 2e- Fe+2  Fe+3 + 1 e- Oxidation number goes up What is the same in these two reactions? Lose electrons

  11. C. Reduction half reactions: GER Cu+2 + 2e- Cu0 Mn+7 + 1e-  Mn+6 S0 + 2e-  S-2 Oxidation number goes down What is the same in these three reactions? Gain electrons

  12. III. Write the oxidation and reduction half reactions from this equation: Ca + S  Ca+2 + S-2 Oxidation Ca  Ca+2 + 2 e- Reduction S + 2 e- S-2

  13. IV. Vocabulary 1. electricity – Flow of electrons 2. voltage – “Force” causing the flow of electrons 3. anode – oxidation reaction 4. oxidation potential – voltage due to oxidation reaction AN OX

  14. IV. Vocabulary (cont.) 5. cathode – reduction reaction 6. reduction potential – voltage due to reduction reaction (switch sign) 7. net voltage – oxidation potential + reduction potential 8. spontaneous reactions - a reaction that occurs on its own positive net voltage

  15. V. Will Sn + Mg+2 react or Mg + Sn+2 ? look on Oxidation ½-rxn chart… Sn  Sn2+ + 2e- V = 0.14 V Mg  Mg2+ + 2e- V = 2.37 V Which reaction can be flipped so the net voltage is still positive ? Sn2+ + 2e- Sn V = - 0.14 V Mg  Mg2+ + 2e- V = 2.37 V Sn2++ Mg  Sn + Mg2+ V = 2.23 V

  16. Will Cu + Ag+1 react or Ag + Cu+2 ? look on Oxidation ½-rxn chart… Cu  Cu2+ + 2e- V = -0.34 V Ag  Ag+1 + 1e- V = -0.80 V Which reaction can be flipped so the net voltage is still positive ? Ag+1 + 1e-  Ag V = 0.80 V Cu  Cu2+ + 2e- V = -0.34 V 2Ag+ + Cu  2Ag + Cu2+ V = 0.46 V 2 2 2

  17. Review If reverse the reaction, what happens to V? If change coefficients, what happens to V?

  18. VI. Electrochemical cells and batteries Electron flow Anode – Oxidation Reaction Zn Zn2+ + 2e- Cathode – Reduction Reaction Cu+2 + 2e- Cu Zn  Zn2+ + 2e- V = 0.76 V Cu2+ + 2e-  Cu V = 0.34 Cu2+ + Zn  Zn2++ Cu V = 1.10 V

  19. Copper Zinc Electrochemical Cell e- V Salt bridge Cu Zn Zn2+ Cu2+

  20. Zn  Zn2+ + 2e- V = 0.76 V Cu2+ + 2e-  Cu V = 0.34 Cu2+ + Zn  Zn2++ Cu V = 1.10 V

  21. VII. If you created a Zn-Ag battery a. Which element will oxidize? Zinc will oxidize (higher up the table) b. Identify the anode and the cathode. Zn = Anode Ag = Cathode c. Write the half reactions. Zn  Zn+2 + 2e- 0.76 V 2 Ag+ + 2e- 2 Ago 0.80 V d. Calculate the net voltage. 1.56 V

  22. VIII. If you created a zinc/iron (II) battery a. Which element will oxidize? Zinc will oxidize (higher up the table) b. Identify the anode and the cathode. Zn = Anode Fe = Cathode c. Write the half reactions. Zn  Zn+2 + 2e-0.76 V Fe+ + 2e- Fe+2 -0.44 V d. Calculate the net voltage. 0.32 V

  23. IX. Galvanized iron Wrapped in Zinc. Which is more likely to oxidize, or ? A “sacrificial” metal like zinc is oxidized, the structural metal, Fe, remains pure Fe Zn

  24. X. Underground storage tanks (iron) • Use sacrificial metals to keep structural metals from oxidizing

  25. XI Aluminum wiring – a fire hazard?? • Aluminum Wire and Copper Connections • Mostly in houses built between 1965-1973 • Battery effect • Gaps from lost metal then lead to sparks, a fire hazard. http://images.google.com/imgres?imgurl=http://www3.telus.net/metrohomeinspections/images/burned_outlet.jpg&imgrefurl=http://www3.telus.net/metrohomeinspections/aluminum.htm&h=132&w=199&sz=5&hl=en&start=20&sig2=8KgC_kYwotKxkR4tQ1DnSw&um=1&tbnid=LVV-n0RtI_83WM:&tbnh=69&tbnw=104&ei=8OVBRofGHo3oiQGWq93aDA&prev=/images%3Fq%3Daluminum%2Bwiring%2Bfire%26svnum%3D10%26um%3D1%26hl%3Den%26sa%3DN

  26. This is a Copper-nickel pump that was feeding sea water to a pure titanium pump down stream. The galvanic action from the titanium pump pulled most of the copper out of the copper-nickel pump. It was only 2 years old and had to be replaced with a glass composite impeller.

  27. Cell or Battery? Electrochemical Cells combine to make batteries AA, AAA, C, and D “batteries” are really cells = 1.5 V

  28. cell battery

  29. How Can You Get a 9-V Battery?

  30. Inside of a Battery Lithium-Ion Cell Alkaline Cell

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