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)+ O 2 (g)  2 MgO (s)ionic bond formation transfer of electrons (formation of cations and anions) H 2 (g) + Cl 2 (g)  2 HCl(g)covalent bond formation shift in electron charge (dipole, polarity)

Exp 19A: Oxidation-Reduction Reactions X Y e-e- transfer or shift of electrons X looses electron(s)Y gains electron(s) X is oxidizedY is reduced X is the reducing agentY is the oxidizing agent X increases its “oxidation number” Y decreases its “oxidation number” Oxidation: loss of electrons Mg  Mg e - Reduction: gain in electrons ½ O 2 + 2e -  O 2- 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

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

Redox Activity of Halogens F 2 > Cl 2 > Br 2 > I 2 Redox potential and reactivity decreases down Group 7A A halogen higher in the periodic system oxidizes one that is lower in the periodic system  Chlorine can oxidize bromide Br - (aq) + Cl 2 (aq)  Br 2 (aq) + 2 Cl - (aq)  Bromine cannot oxidize chloride 2 Cl - (aq) + Br 2 (aq)  no reaction

Exp 19A: Oxidation-Reduction Reactions Goal of the Experiment (II)  Observe redox reactions with permanganate and iron(III) ions  Reduction of –MnO 4 - (permanganate, purple) to MnO 4 2- (manganate, green) –MnO 4 - (permanganate, purple) to MnO 2 (manganese oxide, black solid) –MnO 4 - (permanganate, purple) to Mn 2+ (manganese(II) ion, pink) –Fe 3+ (iron(III), reddish brown) to Fe 2+ (iron(II), pale green)

Exp 19A: Oxidation-Reduction Reactions Cl 2 Solution Reaction 2OCl - + 4H 3 O + + 2e -  Cl 2 + 6H 2 O 2Cl -  Cl 2 + 2e - 2OCl - + 2Cl H 3 O +  2Cl 2 + 6H 2 O or OCl - + Cl H 3 O +  Cl 2 + 3H 2 O Preparation of 12 mL 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 H 2 SO 4 –6.0 mL 0.20 M NaCl –3.1 mL H 2 O –Put in large test tube

Exp 19A: Oxidation-Reduction Reactions Br 2 Solution Reaction 2BrO H 3 O e -  Br H 2 O 10 Br -  5 Br e - 2BrO Br H 3 O +  6 Br H 2 O or BrO Br H 3 O +  3 Br 2 + 9H 2 O Preparation of 12 mL M bromine water –1.0 mL 0.2 M KBrO 3 –5.0 mL 0.20 M NaBr –1.2 ml 0.50 M H 2 SO 4 –Wait 15 minutes before adding: –4.8 mL H 2 O –Put in large test tube

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

Exp 19A: Oxidation-Reduction Reactions Exp 1 Put 15 drops of Cl 2 solution in small test tube Put 15 drops of Br 2 solution in 2 nd small test tube Put 15 drops of I 2 solution in 3 rd 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

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 Br 2 solution to tube 1 Add 10 drops of I 2 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

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 Cl 2 solution to tube 1 Add 10 drops of I 2 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

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 Cl 2 solution to tube 1 Add 10 drops of Br 2 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

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 KMnO 4 solution to tube 1 Add 5 drops of 0.1 M FeCl 3 solution to tube 2 Add 5 drops of 3 M H 2 SO 4 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

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 KMnO 4 solution to tube 1 Add 5 drops of 0.1 M FeCl 3 solution to tube 2 Add 5 drops of 3 M H 2 SO 4 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

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 KMnO 4 solution to tube Add 1 mL cyclohexane to tube Shake or swirl Record color change/observations for both the aqueous and the organic layer

Exp 19A: Oxidation-Reduction Reactions Exp 3: Reactions of Halogens and Halides (1)Cl - + Br 2 : NR: Br 2 is still present (yellow-orange color) (2)Cl - + I 2 : NR: I 2 is still present (violet color) (3)Cl 2 + 2Br -  2Cl - + Br 2 (yellow-orange color) (4)I 2 + 2Br - : NR: I 2 is still present (violet color) (5)Cl 2 + 2I -  2Cl - + I 2 (violet color) (6)Br 2 + 2I -  2Br - + I 2 (violet color)

Exp 19A: Oxidation-Reduction Reactions Exp 3: Reactions of Permanganate and Iron (7)2MnO H 3 O e -  2Mn H 2 O 10Br -  5Br e - 2MnO Br - +16H 3 O +  2Mn Br 2 + 8H 2 O (yellow-orange color) (9)2MnO H 3 O e -  2Mn H 2 O 10I -  5I e - 2MnO I - +16H 3 O +  2Mn I 2 + 8H 2 O (violet color) (8)Fe 3+ + Br -  No color, No Reaction (10)2Fe e -  2Fe 2+ 2I -  I 2 + 2e - 2Fe I -  2Fe 2+ + I 2 (violet color)

Exp 19A: Oxidation-Reduction Reactions Exp 3: Reactions of Permanganate and Iron (11)6MnO e -  6MnO 4 2- I - + 3H 2 O  IO H 3 O + + 6e - 6H 3 O + + 6OH -  6H 2 O 6MnO I - +6OH -  6MnO IO H 2 O green color in aqueous layer no color in cyclohexane no formation of a nonpolar halogen

Exp 19A: Oxidation-Reduction Reactions Post Lab Results sheets (p ) 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