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Oxidation – Reduction Processes

Oxidation – Reduction Processes

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Oxidation – Reduction Processes

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  1. Oxidation – ReductionProcesses

  2. Redox Reaction Any chemical reaction that involves the transfer of one or more electrons between atoms. One reactant gains electrons and the other reactant loses electrons.

  3. Examples of Redox Reactions • Combustion of gasoline • Burning of wood • Energy from food • Bleaching stains • Iron rusting

  4. Reduction • Electrons are fully or partially gained S0(s) + 2 e- S2- electrons gained: written as a reactant

  5. Oxidation • Electrons are fully or partially lost Mg0 (s) Mg 2+ + 2e- Electrons lost: written as a product

  6. Oxidation and Reduction • Opposing reactions • Must occur together • Redox (Reduction – Oxidation)

  7. Mnemonic Device • LEO the lion goes GER LEO: Loss of Electrons is Oxidation GER: Gain of Electrons is Reduction

  8. Mnemonic Device • OIL RIG • Oxidation Is Loss of electrons • Reduction Is Gain of electrons

  9. Complete Redox Reaction • Add together the reduction half-reaction with the oxidation half-reaction to get the complete redox reaction.

  10. Complete Redox Reaction Add together the 2 half-reactions Mg0 (s) Mg 2+ + 2e- Oxidation + S0(s) + 2 e- S2- Reduction Complete Redox Reaction Mg0 (s) + S0(s) Mg 2+ + S2-  Mg + S Mg+2 + S -2

  11. Assigning Oxidation Numbers

  12. Oxidation Numbers • Numbers assigned to all of the elements involved in the reaction to determine if electrons have been transferred between atoms in a reaction.

  13. Oxidation Numbers • The oxidation number is usually equal to the charge on the ion if it was formed.

  14. Rule #1 • Free elements are assigned an oxidation state of 0. • Al = 0 • Na = 0 • H2 = 0

  15. Rule #2 • The oxidation state for any simple one-atom ion is equal to its charge. • Na+ = +1 • Be2+= +2 • F- = -1

  16. Rule #3 • Hydrogen in compounds is assigned an oxidation state of +1.  Exception - Hydrides, ex. LiH (H=-1). • H2SO4: H=+1 • HCl: H=+1

  17. Rule #4 • Oxygen in compounds is assigned an oxidation state of -2. Exception - Peroxide, ex. H2O2 (O = -1). • H3PO4: O=-2 • H2O: O=-2

  18. Rule #5 • The sum of the oxidation numbers of all atoms in a neutral compound is 0. • H2SO4: add up to 0 • CO2: add up to 0

  19. Rule #6 • The sum of the oxidation numbers of all atoms in a polyatomic ionequals the charge on the ion. • SO42-: add up to -2 • NH4+: add up to +1

  20. Examples • Al(s): • Al = ____ Rule #1 0

  21. Examples • CaCl2: • Ca = ____ • Cl=____ Rule #2 Rule #5 (or rule #2) Ca+2 1 (+2) + 2 (Cl) = 0 -1 Cl = -1

  22. Examples • HNO3: • H= ____ • N= ____ • O= ____ Rule # 3 (Hydrogen) Rule # 4 (Oxygen) +1 Rule # 5 (solve for N) +5 1(1) + 1(N) + 3(-2) = 0 -2 N = +5

  23. Examples • SO42-: • S= ____ • O= ____ Applied to: Rule #4 (oxygen) Rule #6 (polyatomics) Solve for S +6 1(S) + 4(-2) = -2 -2 S= +6

  24. Examples • H2O: • H= ____ • O= ____ Rule #3 (hydrogen) Rule #4 (oxygen) +1 -2

  25. Examples 1(N)+4(+1)=+1 • (NH4)2CO3 N= -3 NH4+ CO32- 1(C)+3(-2)=-2 Rule 7 Rule 6 C=+4 Rule 9 -3 +4 • N=____ C=___ • H=____ O=___ +1 -2

  26. Oxidized Element • The substance that loses electrons is the oxidized element (it undergoes oxidation. • Atoms that are oxidized will have an increase in their oxidation number

  27. Oxidized Element Increase in oxidation number Mg0 (s) + S0(s) Mg 2+ + S2- Mg is oxidized

  28. Reduced Element • The substance that gains electrons is the reduced element (it undergoes reduction). • Atoms that are reduced will have an decrease in their oxidation number

  29. Reduced Element Decrease in oxidation number Mg0 (s) + S0(s) Mg 2+ + S2- S is reduced

  30. Oxidizing Agent/Reducing Agent • The element or compound that is reduced is the oxidizer(or oxidizing agent). • The element or compound that is oxidized is the reducer(or reducing agent).

  31. Examples • Are the following redox reactions? • If yes: • What element is oxidized? • What element is reduced? • What is the oxidizing agent? • What is the reducing agent?

  32. Examples +2 -2 0 0 Mg(s) + S(s)  MgS Mg • What element is oxidized? • What element is reduced? • What is the oxidizing agent? • What is the reducing agent? Step # 2: Do the oxidation numbers change? - if no  it is not a redox reaction - if yes  it is a redox reaction Step #1: Assign Oxidation Numbers Yes – It is a redox S S Mg

  33. Examples 0 0 +1 +2 2AgNO3(aq) + Cu(s) Cu(NO3)2(aq) + 2Ag(s) NO3- NO3- Step # 2: Do the oxidation numbers change? - if no  it is not a redox reaction - if yes  it is a redox reaction • What element is oxidized? • What element is reduced? • What is the oxidizing agent? • What is the reducing agent? Cu Ag Yes – It is a redox Step #1: Assign Oxidation Numbers AgNO3(aq) Cu(s)

  34. Check for Understanding 0 0 +3 -2 4Fe(s) + 3O2(g)2Fe2O3(s) • What element is oxidized? • What element is reduced? • What is the oxidizing agent? • What is the reducing agent? Fe Yes O O2 Fe

  35. Check for Understanding +1 -2 +1 +1 -1 +1 -1 +1 -2 HCl + NaOH NaCl + H2O No – it is not a redox

  36. Check for Understanding +1 -1 +1 +1 +1 -1 • NaCl + AgNO3 NaNO3 + AgCl NO3- NO3- No – it is not a redox

  37. Check for Understanding 0 +3 -2 +2 -2 +4 -2 • Fe2O3(s) + 3CO(g) 2Fe(s) + 3CO2(g) • What element is oxidized? • What element is reduced? • What is the oxidizing agent? • What is the reducing agent? C Yes Fe Fe2O3 CO

  38. Any General Rules • Double displacement is NOT typically redox • Single Displacement is ALWAYS redox • Synthesis (from elements) is ALWAYS redox • Decomposition (to elements) is ALWAYS redox