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Oxidation and Reduction Reactions

Oxidation and Reduction Reactions. Magda van Aardt University Senior College Murray.thompson@adelaide.edu.au. Dr Tak Kee Department of Chemistry University of Adelaide. Oxidation and Reduction Reactions.

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Oxidation and Reduction Reactions

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  1. Oxidation and Reduction Reactions Magda van Aardt University Senior College Murray.thompson@adelaide.edu.au Dr Tak Kee Department of Chemistry University of Adelaide

  2. Oxidation and Reduction Reactions “This material has been developed as a part of the Australian School Innovation in Science, Technology and Mathematics Project funded by the Australian Government Department of Education, Science and Training as a part of the Boosting Innovation in Science, Technology and Mathematics Teaching (BISTMT) Programme.”

  3. Refraction and Optical Fibres • When light travels from one medium to another it changes speed. • It also changes direction.

  4. Oxidation and Reduction Redox Reactions

  5. Chemical reaction types Redox reactions can be : * Single replacement reaction * Combination reactions * Decomposition * Combustion reactions Acid-base reactions & double replacement reactions

  6. Redox Reactions Involve a transfer of electrons between reacting species. … Takes place when reduction and oxidation occur simultaneously RED+ OX = REDOX

  7. Redox reactions in batteries

  8. Redox reactions in lead acid batteries h

  9. Redox reactions in photosynthesis 6H2O + 6CO2 + light energy → C6H12O6 + 6O2 http://plantsandalgae/photography_091.jpeg

  10. Cell respiration → Energy = ATP (adenosine triphosphate) Glucose =reductant + + + Carbon dioxide Oxygen=oxidant water Glucose ATP http://biology.clc.uc.edu/Courses/bio104/cellresp.htm

  11. Photography K2Cr2O7

  12. Electrolysis: SALTS AND WATER

  13. Fuel Cells Reduction at Cathode Reduction half equation: ½O2(g)+ 2e- + 2H+ → H2O Oxidation at the anode Oxidation half equation: H2 (g) → 2H+ + 2e- http://p2library.nfesc.navy.mil/issues/emergeoct2005/fuelcell.jpg

  14. Fuel Cells (cont) Space Shuttle Discovery hurtles into space on mission STS-105, August 10, 2001.

  15. Combustion Complete Combustion of propane: C3H8(g) + O2 (g) → 3CO2(g) + 4H2O(g)

  16. Fireworks http://www.chemsoc.org/ExemplarChem/entries/2004/icl_Gondhia/lightcolour.htmlComposition

  17. REDOX REACTIONS IN BLEACHES: H2O2HClOSO2 http://commons.wikimedia.org/wiki/Image:Bleach-bottle.jpg HOCl (aq) is the active ingredient in White King http://www.npr.org/templates/story/story.php?storyId=3892457 http://www.ultrasonic-stain-remover.com/blood_stain_remover.jpg er.com/blood_stain_remover.jpg

  18. Rusting / corrosion Rust = Fe2O3.H2O (the red brown flaky stuff)

  19. Steel making (cont) Fe2O3(S) + CO(g) → 2Fe (l) + 3CO2 (g) +3 +2 0 +4 oxidation reduction

  20. Steel making (cont) Fe2O3 (s)+ 3CO (g) → 2Fe (s) + 3CO2 http://www.bbc.co.uk/history/interactive/animations/blast_furnace/index.shtml

  21. Galvanic Cells Salt bridge = Electrolyte = Solution with ions to carry charge KCl (aq) or NO3(aq) ELECTROLYTES

  22. Electroplating http://www.glenair.com/qwikconnect/vol7num4/electro.jpg

  23. Spin-Coating – a simple way to produce thin films Films of ~100 nm can be routinely produced

  24. Organic Light Emitting Diode (OLED) + Voltage source V volts – Field line + – Device material (Ru2+) Tris(2,2'-bipyridyl) Ruthenium(II) Electron (in the form of Ru+) and hole (Ru3+) migrate towards centre and recombine to produce light – A 3rd year Chem student practical at Adelaide University Positive charge or hole migration Electron migration 24

  25. LESSON 2 OXIDATION AND REDUCTION

  26. REDOX = OXidation + REDuction What is oxidation ? What is reduction?

  27. What is oxidation? OXIDATIONISDEFINED AS : 1: LOSS OF HYDROGEN CH3 OH Cr2O72- → CH2O (methanol) H+ (heat) (methanal)

  28. What is oxidation? OXIDATIONISDEFINED AS : 2: GAIN OF OXYGEN Mg(s) + O2(g) → 2MgO 2Ca (s) + O2(g) → 2CaO

  29. What is oxidation? 3:LOSS OF ELECTRONS =OXIDATION (LEO) OXIDATIONISDEFINED AS :

  30. What is oxidation? 4: INCREASE IN OXIDATION NUMBER Fe (s) → Fe 2+ (aq) + 2e- 0 +2 OXIDATIONISDEFINED AS :

  31. What is reduction? 1: GAIN OF HYDROGEN C3H6 (g) + H2(g) (catalyst) Ni → C3H8(g) (propene) heat pressure (propane) REDUCTIONISDEFINED AS :

  32. What is reduction? REDUCTIONISDEFINED AS : 2: LOSS OF OXYGEN CuO (s) + H2(g) → Cu (s) + H2O (g)

  33. What is reduction? REDUCTIONISDEFINED AS : O2(g) + 4e- → 2O2- (aq) 3:GAIN OF ELECTRONS =REDUCTION (GER)

  34. What is reduction? REDUCTIONISDEFINED AS : 4: DECREASE IN OXIDATION NUMBER Cl2 (g) + 2e- → 2Cl-(aq) -1 0

  35. When is it a redox reaction ? What about this reduction reaction? 2MnO4-(aq)+ 16H+ +10e- → Mn2+(aq)+ 8H2O(l) and this one? Cr2O72-(aq) +14H++6e- → 2Cr3+(aq)+ 7H2O(l)

  36. Rules to determine oxidation numbers Rule1 ELEMENTS: ZERO H2 Li N2 O3 S8 Fe Cu Mg Cl2 O2 F2 uncombined with other elements their oxidation number is

  37. Rules to determine oxidation numbers RULE 2 SIMPLE IONS: H+ =+1 Fe2+ = +2 = -2 O2- Al 3+ = +3 their oxidation number is the charge on the ion :

  38. Rules to determine oxidation numbers RULE 3 OXYGEN: IN COMPOUNDS IS –2 [except in hydrogen peroxide (H2O2 )it is -1 compounds in which it is bounded to fluorine F2O it is +2 ] MgSO4 K2CO3 SO2 CO Na2O P4O10

  39. Rules to determine oxidation numbers RULE 2 MOLECULES: THE SUM OF THE OXIDATION NUMBERS IS: ZERO What is the oxidation number of Phosphorus (P) inP4O10 4(Phosphorus ‘s oxidation number which we will take as x)+10( oxidation number of oxygen) = 0 4 X +10 (-2)= 0 4 X = 20 X=+5X=+IV YOU TRY : S in SO3… and Cl in HClO

  40. Rules to determine oxidation numbers RULE 5 HYDROGEN: =+1 when in compound with a non metal H2O WATER NH4+ AMMONIUM NH3 AMMONIA HCl HYDROCHLORIC ACID

  41. Rules to determine oxidation numbers RULE 6 COMPLEX / POLYATOMIC IONS: THE SUM OF ALL THE OXIDATION NUMBERS IS: CHARGE ON THE ION What is the oxidation number of S in SO42- ? SO42- (oxidation number of S is x) x+ 4 (-2) =-2 x -8 =-2 x= +8-2 x=+6

  42. Using oxidation numbers to identify a redox reaction 0 Rule 1 +1 Rule 5 The oxidation number of hydrogen changes from 0 to +I Increase in oxidation number Hydrogen has been oxidised (undergoes oxidation) Hydrogen is the reductant (reducing agent) Is H2(g) + I2(g) → 2HI (g) a redox reaction?

  43. Using oxidation numbers to identify a redox reaction Is H2(g) + I2(g) → 2HI (g) a redox reaction? 0 Rule 1 -1 Rule 4 and 5 The oxidation number of iodine changes from 0 to – I Decrease in oxidation number Iodine has been reduced (undergoes reduction) Iodine acts as the oxidant (oxidising agent)

  44. Using oxidation numbers to identify a redox reaction Is H2(g) + I2(g) → 2HI (g) a redox reaction? -1 Rule 4+5 0 Rule 1 0 Rule 1 +1 Rule 5 Yes, oxidation number has changed for different chemical species

  45. Using oxidation numbers to identify a redox reaction +1 Rule 5 0 Rule 1 +2 0 -2 +6 +6 -2 The oxidation number of magnesium changes from 0 to +2 Increase in oxidation number Magnesium metal has been oxidised (undergoes oxidation) Magnesium metal (Mg) is the reductant (reducing agent) The oxidation number of H (in H2SO4 changes from +1 to 0 (in H2) Decrease in oxidation number H2SO4 has been reduced (undergoes reduction) H2SO4 acts as the oxidant (oxidising agent) • Mg(s) + H2SO4 (aq) → MgSO4 (aq) + H2 (g)

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