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Exp 19A: Oxidation-Reduction Reactions

Exp 19A: Oxidation-Reduction Reactions. Oxidation-Reduction (Redox) reactions Net movement of electrons from one reactant to the other Movement from reactant with less attraction to reactant with more attraction for electrons (larger electron affinity )

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Exp 19A: Oxidation-Reduction Reactions

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  1. Exp 19A: Oxidation-Reduction Reactions Oxidation-Reduction (Redox) reactions Net movement of electrons from one reactant to the other Movement from reactant with less attraction to reactant with more attraction for electrons (larger electron affinity) Occurs in both ionic and covalent bond formation Examples 2 Mg(s)+ O2(g)  2 MgO (s)ionic bond formation transfer of electrons (formation of cations and anions) H2(g) + Cl2(g)  2 HCl(g)covalent bond formation shift in electron charge (dipole, polarity)

  2. e- Y X Exp 19A: Oxidation-Reduction Reactions Oxidation: loss of electrons Mg  Mg2+ + 2e- Reduction: gain in electrons ½ O2 + 2e-  O2- transfer or shift of electrons X looses electron(s) Y gains electron(s) X is oxidized Y is reduced X is the reducing agent Y is the oxidizing agent X increases its “oxidation number” Y decreases its “oxidation number” • reducing agents loose electrons while oxidizing agents gain electrons simultaneously • a chemical change cannot be an “oxidation reaction” or just a “reduction reaction” • it is always an “oxidation-reduction” reaction

  3. Exp 19A: Oxidation-Reduction Reactions Goal of the Experiment (I) Observe redox reactions between halogens (oxidizers) and halogen ions (halides, reducers) in cyclohexane Halide ions (polar!) are insoluble in non-polar cyclohexane Halogens (non-polar!) are soluble in cyclohexane If a reaction takes place, the color in the cyclohexane may be different from the color in water, but ….. You have to make very careful observations and THINK about the results

  4. Redox Activity of Halogens F2 > Cl2 > Br2 > I2 Redox potential and reactivity decreases down Group 7A A halogen higher in the periodic system oxidizes one that is lowerin the periodic system Chlorine can oxidize bromide -100-1 2 Br- (aq) + Cl2 (aq)  Br2 (aq) + 2 Cl- (aq) Bromine cannot oxidize chloride 2 Cl- (aq) + Br2(aq)  no reaction

  5. Exp 19A: Oxidation-Reduction Reactions Goal of the Experiment (II) Observe redox reactions with permanganate and iron(III) ions Reduction of MnO4- (permanganate, purple) to MnO42- (manganate, green) MnO4- (permanganate, purple) to MnO2 (manganese oxide, black solid) MnO4- (permanganate, purple) to Mn2+ (manganese(II) ion, pink) Fe3+ (iron(III), reddish brown) to Fe2+(iron(II), pale green)

  6. Exp 19A: Oxidation-Reduction Reactions Cl2 Solution • Reaction 2OCl- + 4H3O+ + 2e-  Cl2 + 6H2O 2Cl- Cl2 + 2e- 2OCl- + 2Cl- + 4 H3O+ 2Cl2 + 6H2O or OCl- + Cl- + 2 H3O+ Cl2 + 3H2O • Preparation of 12 mL 0.050 M chlorine water (add in this order and in the fume hood and leave it there!) • 1.70 mL bleach (NaOCl) • 1.2 ml 0.50 M H2SO4 • 6.0 mL 0.20 M NaCl • 3.1 mL H2O • Put in large test tube

  7. Exp 19A: Oxidation-Reduction Reactions Br2 Solution • Reaction 2BrO3- + 12 H3O+ + 10e- Br2 + 18H2O 10 Br- 5 Br2+ 10e- 2BrO3- + 10 Br- + 12 H3O+ 6 Br2 + 18H2O or BrO3- + 5 Br- + 6 H3O+ 3 Br2 + 9H2O • Preparation of 12 mL 0.050 M bromine water • 1.0 mL 0.2 M KBrO3 • 5.0 mL 0.20 M NaBr • 1.2 ml 0.50 M H2SO4 • Wait 15 minutes before adding: • 4.8 mL H2O • Put in large test tube

  8. Exp 19A: Oxidation-Reduction Reactions I2 Solution • Reaction 2Cu2+ + 2I- + 2e- 2CuI 2I- I2 + 2e- 2Cu2+ + 4I- 2CuI + I2 • Preparation of 12 mL 0.050 M iodine water • 6.0 mL 0.20 M CuSO4 • 6.0 mL 0.40 M NaI • Filter over double filter paper to remove insoluble CuI • Put solution in large test tube

  9. Exp 19A: Oxidation-Reduction Reactions Exp 1 • Put 15 drops of Cl2 solution in small test tube • Put 15 drops of Br2 solution in 2nd small test tube • Put 15 drops of I2 solution in 3rd small test tube • Add 1 mL cyclohexane to each tube • Shake or swirl solution gently • Record colors (if any) in cyclohexane layer • Keep these tubes as reference colors

  10. Exp 19A: Oxidation-Reduction Reactions Exp 2: Reactions of Halogens with Halides (I) • Put 10 drops of 0.2 M NaCl in 2 clean and dry test tubes • Add 10 drops of Br2 solution to tube 1 • Add 10 drops of I2 solution to tube 2 • Add 1 mL cyclohexane to each tube • Shake or swirl • Record color change for both the aqueous and the organic layer • NO reaction: cyclohexane will have color of aqueous layer • Reaction: color change in cyclohexane

  11. Exp 19A: Oxidation-Reduction Reactions Exp 2: Reactions of Halogens with Halides (II) • Clean test tubes • Put 10 drops of 0.2 M NaBr in 2 clean and dry test tubes • Add 10 drops of Cl2 solution to tube 1 • Add 10 drops of I2 solution to tube 2 • Add 1 mL cyclohexane to each tube • Shake or swirl • Record color change for both the aqueous and the organic layer

  12. Exp 19A: Oxidation-Reduction Reactions Exp 2: Reactions of Halogens with Halides (III) • Clean test tubes • Put 5 drops of 0.4 M NaI in 2 clean and dry test tubes • Add 10 drops of Cl2 solution to tube 1 • Add 10 drops of Br2 solution to tube 2 • Add 1 mL cyclohexane to each tube • Shake or swirl • Record color change for both the aqueous and the organic layer

  13. Exp 19A: Oxidation-Reduction Reactions Exp 3: Reactions of Permanganate and Iron (I) • Clean test tubes • Put 15 drops of 0.2 M NaBr in two test tubes • Add 1 drop of 0.1 M KMnO4 solution to tube 1 • Add 5 drops of 0.1 M FeCl3 solution to tube 2 • Add 5 drops of 3 M H2SO4 to each tube • Add 1 mL cyclohexane to each tube • Shake or swirl • Record color change/observations for both the aqueous and the organic layer

  14. Exp 19A: Oxidation-Reduction Reactions Exp 3: Reactions of Permanganate and Iron (II) • Clean test tubes • Put 8 drops of 0.4 M NaI in two test tubes • Add 1 drop of 0.1 M KMnO4 solution to tube 1 • Add 5 drops of 0.1 M FeCl3 solution to tube 2 • Add 5 drops of 3 M H2SO4 to each tube • Add 1 mL cyclohexane to each tube • Shake or swirl • Record color change/observations for both the aqueous and the organic layer

  15. Exp 19A: Oxidation-Reduction Reactions Exp 3: Reactions of Permanganate and Iron (III) • Clean test tubes • Put 8 drops of 0.4 M NaI in one test tube • Add 5 drop of 6.0 M NaOH solution to tube • Add 1 drop of 0.1 M KMnO4 solution to tube • Add 1 mL cyclohexane to tube • Shake or swirl • Record color change/observations for both the aqueous and the organic layer

  16. Exp 19A: Oxidation-Reduction Reactions Exp 3: Reactions of Halogens and Halides • Cl- + Br2: NR: Br2 is still present (yellow-orange color) • Cl- + I2: NR: I2 is still present (violet color) • Cl2 + 2Br- 2Cl- + Br2 (yellow-orange color) • I2 + 2Br-: NR: I2 is still present (violet color) • Cl2 + 2I- 2Cl- + I2 (violet color) • Br2 + 2I- 2Br- + I2 (violet color)

  17. Exp 19A: Oxidation-Reduction Reactions Exp 3: Reactions of Permanganate and Iron (7) 2MnO4- + 16H3O+ + 10e- 2Mn2+ + 8H2O 10Br- 5Br2 + 10e- 2MnO4- + 10Br- +16H3O+ 2Mn2+ + 5Br2 + 8H2O (yellow-orange color) (9) 2MnO4- + 16H3O+ + 10e- 2Mn2+ + 8H2O 10I- 5I2 + 10e- 2MnO4- + 10I- +16H3O+ 2Mn2+ + 5I2 + 8H2O (violet color) (8) Fe3+ + Br-  No color, No Reaction (10) 2Fe3+ + 2 e- 2Fe2+ 2I-  I2 + 2e- 2Fe3+ + 2I-  2Fe2+ + I2 (violet color)

  18. Exp 19A: Oxidation-Reduction Reactions Exp 3: Reactions of Permanganate and Iron (11) 6MnO4- + 6e- 6MnO42- I- + 3H2O  IO3- + 6H3O+ + 6e- 6H3O+ + 6OH-  6H2O 6MnO4- + I- +6OH- 6MnO42- + IO3- + 3H2O green color in aqueous layer no color in cyclohexane no formation of a nonpolar halogen

  19. Exp 19A: Oxidation-Reduction Reactions Post Lab • Results sheets (p. 351-352) • Post lab questions 1, 2a-d, 3a-c • Give balanced equations for every reaction that happened • If there was no reaction, write “NR” and indicate how you reached that conclusion • Answer the questions

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