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Chapter 3

Chapter 3. Oxidation & Reduction. Redox Reactions. oxidation and reduction occurring simultaneously. can be explained based on:. Gains oxygen. Loses hydrogen. Loses electrons. ↑ in oxi number. Example 1:. oxidised. reduced. Example 2:. oxidised. reduced. Example 3:. reduced.

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Chapter 3

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  1. Chapter 3 Oxidation & Reduction

  2. Redox Reactions • oxidation and reduction occurring simultaneously • can be explained based on: Gains oxygen Loses hydrogen Loses electrons ↑ in oxi number

  3. Example 1: oxidised reduced

  4. Example 2: oxidised reduced

  5. Example 3: reduced oxidised

  6. Example 1:

  7. Example 2:

  8. a.The oxidation number of atoms and molecules of elements is zero

  9. b.The oxidation number for a simple ion is similar to the charge of the ion.

  10. example example

  11. Exercise

  12. Exercise

  13. example

  14. 3 types of equations: • Oxidation half equation  Reduction half equation  Ionic equation (oxi ½ eq + red ½ eq)

  15. Example 1:  oxidised X 2 Al  Al3+ + 3e  Cu2+ + 2e  Cu X 3 2Al + 3CuSO4 Al2(SO4)3 + 3Cu 2Al  2Al3+ + 6e 0+2+6-2+3+6-20 3Cu2+ + 6e  3Cu  reduced 2Al + 3Cu2+ 2Al3+ + 3Cu

  16. Example 2: oxidised  Mg  Mg2+ + 2e Mg + 2AgNO3 Mg(NO3)2 + 2Ag  Ag+ + e  Ag X 2 0+1+5-2+2+5-20  Mg + 2Ag+ Mg2+ + 2Ag reduced

  17. (A) Redox Reaction in the Displacement of Metals from its Salt Solution Most reactive metal Potassium K Sodium Na Calcium Ca Magnesium Mg Aluminium Al Zinc Zn Iron Fe Tin Sn Lead Pb [Hydrogen] [ H ] Copper Cu Mercury Hg Silver Ag Gold Au Electrochemical Series: More electropositive An arrangement of metals based on the tendency of each metal atom to donate/release electrons to form a positive ion (cation). More easier release ē K  K+ + ē More easier to form ion Least reactive metal

  18. (A) Redox Reaction in the Displacement of Metals from its Salt Solution Potassium K Sodium Na Calcium Ca Magnesium Mg Aluminium Al Zinc Zn Iron Fe Tin Sn Lead Pb [Hydrogen] [ H ] Copper Cu Mercury Hg Silver Ag Gold Au Example of experiment : Observation thinner • Zn plate become _________________ • blue colour of CuSO4 solution become ______________ • a ____________ solid is formed colourless brown ? Any observable changes? • Zn atom is able to displace the copper (II) ions • Zn atom form __________________ • Cu2+ ion form __________________ zinc ion, Zn2+ copper atom, Cu Oxi ½ eq Zn  Zn2+ + 2e Red ½ eq Cu2+ Cu + 2e Ionic eq Zn + Cu2+ Zn2+ + Cu

  19. Electrode Carbon Cu Plate Zn Plate NaCl solution NaCl solution Electrical Chemical energy energy Chemical Electrical energy energy An electrolytic cell A Voltaic Cell Differences Cell Structure Type of electrodes Carbon or 2 same metals or 2 different metals. 2 Different metals. Electric current Produced from chemical reactions. Used to produce chemical reactions. Conversion of energy +terminal (+charged) Anode – terminal ( – charged) – terminal ( – charged) +terminal (+charged) Cathode

  20. An electrolytic cell Differences A Voltaic Cell ē flow from +terminal – terminal ē flow from –terminal + terminal Electrode Carbon Cu Plate Zn Plate NaCl solution NaCl solution +terminal :Donation of ē (–ē)– terminal : Acceptance of ē (+ē) Uses battery IN TERM OF REDOX REACTION Flow of ē OXIDATION REDUCTION Requirement of battery +terminal : Acceptance of ē (+ē)– terminal : Donation of ē (–ē) Type of reaction Requirement of battery • Do not uses battery REDUCTION OXIDATION

  21. Redox Reaction in Corrosion of Metal / Rusting of Iron 3) 3) 4) 4) 2) 2) 1) oxygen • Rusting is the corrosion of iron. For iron to rust, _______ and _______ must be present. water • Corrosion of metal is a redox reaction in which a metal is • oxidised naturally to its ions, resulting in partial or complete • destruction of the metal. cathode cathode anode O2 (g) + 2H2O (l) + 4e- → 4OH- (aq ) O2 (g) + 2H2O (l) + 4e- → 4OH- (aq ) Fe (s) → Fe2+ (aq) + 2 e- Rusting as a redox reaction • Rusting is the corrosion of iron • oxygen acts as the oxidizing agent • iron acts as the reducing agent

  22. Others metals and rusting of iron K Na Ca Mg Al Zn Fe Sn Pb Cu Hg Ag Au • When two metals are in contact with each other, • the more electropositive metal will corrode.

  23. Chlorine is the strongest oxidising agent Iodide ion is the strongest reducing agent Redox Reaction In Displacement of Halogen From Its Halide Solution. • Halogen are good oxidising agents • strength of halogens as [o] agents  whengo down group 17 More reactive halogen displaces less reactive halogen from its halide solution.

  24. Redox Reaction In Displacement of Halogen From Its Halide Solution. Determine whether the following reactions will occur.  a. Bromine, Br2 + Potassium chloride, KCl ( ) b. Chlorine, Cl2 + Potassium bromide, KBr ( ) c. Bromine, Br2 + Potassium iodide, KI ( ) d. Chlorine, Cl2 + Potassium iodide, KI ( ) e. Iodine, I2 + Potassium chloride, KBr ( ) f. Iodine, I2 + Potassium chloride, KCl ( )    reduced   Cl2 + 2KBr  2KCl + Br2 0+1-1+1-10 oxidised More reactive halogen displaces less reactive halogen from its halide solution.

  25. Redox Reaction In Displacement of Halogen From Its Halide Solution. • The presence of halogens is confirmed using an organic • solvent such as 1,1,1-trichloroethane, CH3CCl3

  26. Cl2 (aq) + 2KBr (aq) → Br2(aq) + 2KCl (aq) Br2 Cl2 (aq) + 2KI (aq) → I2(aq) + 2KCl (aq) I2 No observable changes Br2 Br2 (aq) + 2KI (aq) → I2(aq) + 2KBr (aq) I2 No observable changes I2 No observable changes I2 Reference

  27. Fe2+ (aq) → Fe3+ (aq) + e- Redox Reaction In The Change Of Fe2+ Fe3+ and Fe3+ Fe2+ • Iron exhibits two oxidation numbers: • +2 as iron(II) ion,Fe2+[ pale green aqueous solution] • +3 as iron(III) ion,Fe3+[yellow/yellowish brown/brown] oxidation • Changing iron(II) ions to irons(III) ions is an ___________ • ______________ agent: • Br2 water, Cl2 water, KMnO4 / H+, K2Cr2O7 / H+, H2O2 and • conc. HNO3. Fe2+ (aq) → Fe3+ (aq) + e- Oxidising X 2 Oxi ½ eq 2 2 2 Red ½ eq Cl2 Cl- + 2e- 2 Ionic eq 2Fe2+ (aq) + Cl2 (aq) → 2Fe3+ (aq) + 2Cl- (aq)

  28. Fe3+ (aq) → Fe2+(aq) + e- Redox Reaction In The Change Of Fe2+ Fe3+ and Fe3+ Fe2+ • Iron exhibits two oxidation numbers: • +2 as iron(II) ion,Fe2+[ pale green aqueous solution] • +3 as iron(III) ion,Fe3+[yellow/yellowish brown/brown] reduction • Changing iron(III) ions to irons(II) ions is an ___________ • ______________ agent: • More electropositive metal than Fe such as Zn & Mg, SO2, H2S, • sodium sulphite solution, Na2SO3 and tin(II) chloride solution, SnCl2 Fe3+ (aq) → Fe2+ (aq) + e- Reducing Oxi ½ eq Mg  Mg2+ + 2e- Red ½ eq 2 2 2 X 2 Ionic eq 2Fe3+ (aq) + Mg (s) → 2Fe2+ (aq) + Mg2+ (aq)

  29. Redox Reaction In Transfer of Electron at a Distance e • Reducing and oxidizing agents are separated by an electrolyte • in a U-tube • electrons transfer through the connecting wires and can be • detected by a galvanometer • Electrons : from the reducing agent to the oxidizing agent

  30. Example: ELECTRON TRANSFER AT A DISTANCE Br2 water KMnO4/H+ CuSO4 solution KI solution Fe2+ Fe3+ + e 2I - I2 + 2e Br2 + 2e  2Br - MnO4- + 8H+ + 5e  Mn 2+ + 4H2O 2Fe2++ Br22Fe3+ + 2Br -

  31. Types Of Redox Reactions

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