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Redox Reactions

Redox Reactions. Redox Reactions Oxidation - Reduction reactions Terms Oxidation loss of electrons electrons are a product Na --> Na + + e - Reduction gain of electrons electrons are a reactant Br 2 + 2e - --> 2Br -. Oxidizing Agent

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Redox Reactions

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  1. Redox Reactions • Redox Reactions Oxidation - Reduction reactions • Terms Oxidation loss of electrons electrons are a product Na --> Na+ + e- Reduction gain of electrons electrons are a reactant Br2 + 2e- --> 2Br-

  2. Oxidizing Agent Reactant that causes the oxidation (this reactant will be reduced) Reducing Agent Reactant that causes the reduction (this reactant will be oxidized) Oxidation Number charge on an atom can be explicit or implicit oxidation number of elements = 0 Na+ oxidation number = +1 Br - oxidation number = -1

  3. What is the oxidation number of iron in ferric chloride? • +1 • +2 • +3 • -1 • -2

  4. What is the oxidation number of iron in ferric chloride? Ferric chloride = ? Chloride has a charge of? So iron has to be? FeCl3 -1 +3

  5. What is the oxidation number on S in sulfur dioxide? • +2 • +4 • +6 • -2 • -4

  6. SO2 What is the oxidation number on S in sulfur dioxide? sulfur dioxide = ? most of the time, oxygen in combination is the oxide oxygen. So each oxygen has an oxidation number of ? the molecule has to have an overall charge of 0 S + 2(-2) = 0 S = +4 -2

  7. What is the oxidation number of Cr in CrO4-2? • +4 • +6 • +8 • -4 • -2

  8. Chromate ion What is the oxidation number of Cr in CrO4-2? CrO4-2 is called? ion has a charge of -2 Cr + 4(O) = -2 Cr + 4(-2) = -2 Cr = +6

  9. 2 2 2 Na -- > 2 Na+ + 2e- Oxidation half reaction Na + Br2 --> NaBr Reduction half reaction Br2 + 2e- -- > 2 Br- 2 Na + Br2 -- > 2 NaBr

  10. Balancing Redox Reaction Ion Electron Method Split the reaction into half reactions and balance each half reaction • Balance all elements other than H and O • Balance O by adding H2O • Balance H by adding H+. If the reaction is in acid go to 4, if in base go to 3A. 3A. If the reaction is in base, add OH- equal to the number of H+ to both sides of the equation. Combine the H+ andOH- that are on the same side to make H2O • Balance the charge by adding e- • Multiply the 2 half reactions so that the number of electrons is the same in each half reaction • Add the half reactions back together and eliminate redundancies

  11. acid 2 + 14H+ + 6e- +7H2O +6 +12 Cr2O7-2 + SO3-2 --> Cr+3 + SO4-2 Cr2O7-2 --> Cr+3 SO3-2 --> SO4-2 + 2e- 3( H2O + + 2H+ - 2 0 4 8 Cr2O7-2 --> Cr+3 2 + 14H+ + 6e- +7H2O SO3-2 --> SO4-2 3 3 3 H2O + + 6H+ + 6e- Cr2O7-2 +8H+ +3SO3-2 -->2Cr+3 + 4H2O + 3SO4-2

  12. base MnO4- + C2O4-2 --> MnO2 + CO2 -1 -4 3e-+ + 2 H2O MnO4- --> MnO2 + 4OH- 2( + 4H+ + 4OH- 4H2O 0 -2 2e- C2O4-2 --> + CO2 2 3( 4 6e-+ + 4 H2O 2MnO4- --> 2MnO2 + 8OH- + 8H2O 6e- 3C2O4-2 --> + CO2 6 2MnO4- +4H2O+3C2O4-2-->2MnO2+ 8OH- + 6CO2

  13. Br2 + OH- --> BrO3- + Br - + H2O Reaction where the same reactant is both oxidized and reduced disproportionation - 2 - 12 +12H+ 2 Br2 --> BrO3- + 6H2O + 12OH - +12OH- +10e- 12H2O 0 -2 5( + 2e- Br2 --> Br - 2 6 + 12H2O 2 Br2 --> BrO3- + 6H2O + 12OH - +10e- 5 Br2 + 10e- --> 10 Br- Br2 + 5 Br2 + 12OH- --> 2 BrO3- + 6 H2O + 10 Br-

  14. Redox titration a known concentration of oxidizing agent is used to find an unknown concentration of reducing agent (or vice versa)

  15. 37.5 mL of 0.658 M KMnO4 solution were required to completely react with 22.0 mL of a basic K2C2O4soluiton. What is the concentration of the oxalate solution? • 0.748 M • 1.12 M • 1.68 M • 3.89 M • 0.579 M 2MnO4- +4H2O+3C2O4-2-->2MnO2+ 8OH- + 6CO2

  16. 37.5 mL of o 658 M KMnO4 solution were required to completely react with 22.0 mL of a basic K2C2O4soluiton. What is the concentration of the oxalate solution? • Balance the redox reaction. K+ is spectator. 4H2O + 2MnO4- + 3C2O4-2 --> 2MnO2 + 6CO2 + 8OH- 2. Concentration = M = moles C2O4-2/ L. So, need to find moles C2O4-2. Use the moles of MnO4-2 and the mole ratio from the balanced reaction.

  17. 37.5 mL of 0. 658 M KMnO4 solution were required to completely react with 22.0 mL of a basic K2C2O4soluiton. What is the concentration of the oxalate solution? 4H2O + 2MnO4- + 3C2O4-2 --> 2MnO2 + 6CO2 + 8OH- Moles = ? Moles = VM

  18. Activity Series oxidation series that shows the relative reactivity of metals

  19. --> Li+ Reactions are oxidation reactions. --> Ca+2 Metals react with ions that lie below them. • Li • K • Ba • Ca • Na • Mg • Al • Mn • Zn • Cr • Fe • Cd • Co • Ni • Sn • Pb • H2 • Cu • Hg • Ag • Au --> Al+3 Li + Ca+2 --> Li+ + Ca --> Zn+2 Al + Cd+2 --> Al+3 + Cd NR Al + Ca+2 --> ? --> Cd+2 Reactions occur top left with bottom right

  20. Which of the following combination will react? Li+ and Ca Ca+2 and Mg Ca and K+ Ni and H+ Ni and Sn --> Li+ --> Ca+2 --> Al+3 • Li • K • Ba • Ca • Na • Mg • Al • Mn • Zn • Cr • Fe • Cd • Co • Ni • Sn • Pb • H2 • Cu • Hg • Ag • Au --> Zn+2 --> Cd+2

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