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Notes on Electrolytic Cells An electrolytic cell is a system of two inert (nonreactive) electrodes (C or Pt) and an electrolyte connected to a power supply.

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Presentation on theme: "Notes on Electrolytic Cells An electrolytic cell is a system of two inert (nonreactive) electrodes (C or Pt) and an electrolyte connected to a power supply."— Presentation transcript:

1 Notes on Electrolytic Cells An electrolytic cell is a system of two inert (nonreactive) electrodes (C or Pt) and an electrolyte connected to a power supply. It has the following characteristics 1.Nonspontaneous redox reaction 2.Produces chemicals from electricity 3.Forces electrolysis to occur

2 When analyzing an electrolytic cell, your first and most important step is to determine the oxidation and reduction reactions. Electrolytic Cell Main Rule The electrode that is connected to the -ve terminal of the power supply will gain electrons and therefore be the site of reduction.

3 Other Rules: For Electrochemical and Electrolytic Cells Oxidation always occurs at the anode and reduction at the cathode Electrons flow through the wire and go from anode to cathode Anions (- ions) migrate to the anode and cations (+ions) migrate towards the cathode.

4 1. Draw and completely analyze a molten NaBr electrolytic cell.

5 Draw a beaker, two inert electrodes wired to a power supply.

6 1. Draw and completely analyze a molten NaBr electrolytic cell. Draw a beaker, two inert electrodes wired to a power supply. Power Supply DC - +

7 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Supply DC - + Label the electrode with Pt or C.

8 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Supply DC - + Pt Label the electrode with Pt or C.

9 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Supply DC - + Pt Add the electrolyte

10 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Supply DC - + Pt Add the electrolyte Molten or liquid means no water! Na + Br -

11 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Supply DC - + Pt Label the negative and positive electrodes Na + Br -

12 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Supply DC - + Pt Label the negative and positive electrodes Na + Br - _ +

13 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt The negative is reduction and the positive is oxidation. Na + Br - _ +

14 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt The negative is reduction and the positive is oxidation. Na + Br - _ reduction + oxidation

15 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt The anode is oxidation and the cathode is reduction. Na + Br - _ reduction cathode + oxidation anode

16 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt The anion migrates to the anode and the cation to the cathode. Na + Br - _ reduction cathode + oxidation anode

17 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt The anode reaction is the oxidation of the anion. Na + Br - _ reduction cathode + oxidation anode

18 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt The anode reaction is the oxidation of the anion. Na + Br - _ reduction cathode + oxidation anode 2Br - → Br 2(g) + 2e -

19 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt The Cathode reaction is the reduction of the cation. Na + Br - _ reduction cathode + oxidation anode 2Br - → Br 2(g) + 2e -

20 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt The Cathode reaction is the reduction of the cation. Na + Br - _ reduction cathode 2Na + + 2e - → 2Na (l) + oxidation anode 2Br - → Br 2(g) + 2e -

21 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt Gas Br 2 is produced at the anode. Na + Br - _ reduction cathode 2Na + + 2e - → 2Na (l) + oxidation anode 2Br - → Br 2(g) + 2e -

22 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt Liquid Na is produced at the cathode. Na + Br - _ reduction cathode 2Na + + 2e - → 2Na (l) + oxidation anode 2Br - → Br 2(g) + 2e -

23 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt The potential for each half reaction is calculated and the oxidation sign is reversed Na + Br - _ reduction cathode 2Na + + 2e - → 2Na (l) + oxidation anode 2Br - → Br 2(g) + 2e -

24 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt The potential for each half reaction is listed and the oxidation sign is reversed Na + Br - _ reduction cathode 2Na + + 2e - → 2Na (l) -2.71 v + oxidation anode 2Br - → Br 2(g) + 2e - -1.09 v

25 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt The overall redox reaction is written. Na + Br - _ reduction cathode 2Na + + 2e - → 2Na (l) -2.71 v + oxidation anode 2Br - → Br 2(g) + 2e - -1.09 v

26 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt The overall redox reaction is written. Na + Br - _ reduction cathode 2Na + + 2e - → 2Na (l) -2.71 v + oxidation anode 2Br - → Br 2(g) + 2e - -1.09 v 2Na + + 2Br - → Br 2(g) + 2Na (l) E 0 = -3.80 v

27 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt Na + Br - _ reduction cathode 2Na + + 2e - → 2Na (l) -2.71 v + oxidation anode 2Br - → Br 2(g) + 2e - -1.09 v 2Na + + 2Br - → Br 2(g) + 2Na (s) E 0 = -3.80 v The minimum theoretical voltage MTV required to force this nonspontaneous reaction to occur is the negative of the cell potential.

28 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt The minimum theoretical voltage MTV required to force this nonspontaneous reaction to occur is the negative of the cell potential. Na + Br - _ reduction cathode 2Na + + 2e - → 2Na (l) -2.71 v + oxidation anode 2Br - → Br 2(g) + 2e - -1.09 v 2Na + + 2Br - → Br 2(g) + 2Na (s) E 0 = -3.80 v MTV = +3.80 v

29 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt Na + Br - _ reduction cathode 2Na + + 2e - → 2Na (l) -2.71 v + oxidation anode 2Br - → Br 2(g) + 2e - -1.09 v 2Na + + 2Br - → Br 2(g) + 2Na (s) E 0 = -3.80 v MTV = +3.80 v Electrons flow through the wire from anode to cathode.

30 1. Draw and completely analyze a molten NaBr electrolytic cell. Power Source - + Pt Electrons flow through the wire from anode to cathode. Na + Br - _ reduction cathode 2Na + + 2e - → 2Na (l) -2.71 v + oxidation anode 2Br - → Br 2(g) + 2e - -1.09 v 2Na + + 2Br - → Br 2(g) + 2Na (s) E 0 = -3.80 v MTV = +3.80 v e-e- e-e-

31 2. Draw and completely analyze a 1.0 M KI electrolytic cell.

32 Power Source - + Pt

33 2. Draw and completely analyze a 1.0 M KI electrolytic cell. Power Source - + Pt K+I-H2OK+I-H2O Add the ions. (aq) or M or solution means water.

34 2. Draw and completely analyze a 1.0 M KI electrolytic cell. Power Source - + Pt K+I-H2OK+I-H2O Label the -, +, anode, cathode, oxidation, and reduction.

35 2. Draw and completely analyze a 1.0 M KI electrolytic cell. Power Source - + Pt K+I-H2OK+I-H2O Label the -, +, anode, cathode, oxidation, and reduction. - Cathode reduction + Anode oxidation

36 2. Draw and completely analyze a 1.0 M KI electrolytic cell. Power Source - + Pt K+I-H2OK+I-H2O The cation and water migrate to the cathode - Cathode reduction + Anode oxidation

37 2. Draw and completely analyze a 1.0 M KI electrolytic cell. Power Source - + Pt K+I-H2OK+I-H2O The cation and water migrate to the cathode - Cathode reduction + Anode oxidation

38 2. Draw and completely analyze a 1.0 M KI electrolytic cell. Power Source - + Pt K+I-H2OK+I-H2O The cation or water reduces. The higher one on the chart is most spontaneous and occurs. - Cathode reduction + Anode oxidation

39 Cl 2 + 2e- → 2Cl-1.36 v 1/2O 2 + 2H + (10 -7 M) + 2e - → H 2 0 0.82 v 2H 2 O + 2e - → 2H 2 + 2OH - -0.42 v Zn 2+ + 2e - → Zn (s) -0.76 v K + + 1e - → K (s) -2.93 v

40 Cl 2 + 2e - → 2Cl-1.36 v 1/2O 2 + 2H + (10 -7 M) → H 2 0 0.32 v Reduction of water 2H 2 O + 2e - → 2H 2 + 2OH - -0.42 v Zn 2+ + 2e - → Zn (s) -0.76 v K + + 1e - → K (s) -2.93 v

41 Cl 2 + 2e - → 2Cl-1.36 v 1/2O 2 + 2H + (10 -7 M) → H 2 0 0.32 v Oxidation of water Reduction of water 2H 2 O + 2e - → 2H 2 + 2OH - -0.42 v Zn 2+ + 2e - → Zn (s) -0.76 v K + + 1e - → K (s) -2.93 v

42 Cl 2 + 2e - → 2Cl-1.36 v 1/2O 2 + 2H + (10 -7 M) → H 2 0 0.32 v Oxidation of water Reduction of water 2H 2 O + 2e - → 2H 2 + 2OH - -0.42 v Zn 2+ + 2e - → Zn (s) -0.76 v Reduction of K + K + + 1e - → K (s) -2.93 v

43 Cl 2 + 2e - → 2Cl-1.36 v 1/2O 2 + 2H + (10 -7 M) → H 2 0 0.32 v Oxidation of water strongest oxidizing agent or highest Reduction of waterselect most spontaneous reaction 2H 2 O + 2e - → 2H 2(g) + 2OH - -0.42 v Zn 2+ + 2e - → Zn (s) -0.76 v Reduction of K K + + 1e - → K (s) -2.93 v Overpotential Effect- treat water as if it were just below Zn

44 The overpotential effect is a higher than normal voltage required for the half reaction. This is often due to extra voltage required to produce a gas bubble in solution.

45 2. Draw and completely analyze a 1.0 M KI electrolytic cell. Power Source - + Pt K+I-H2OK+I-H2O The cation or water reduces. The higher one on the chart is most spontaneous and occurs. - Cathode Reduction + Anode oxidation

46 2. Draw and completely analyze a 1.0 M KI electrolytic cell. Power Source - + Pt K+I-H2OK+I-H2O The cation or water reduces. The higher one on the chart is most spontaneous and occurs. - Cathode Reduction 2H 2 O+2e - → 2H 2 + 2OH - -0.41 v + Anode oxidation

47 2. Draw and completely analyze a 1.0 M KI electrolytic cell. Power Source - + Pt K+I-H2OK+I-H2O The anion + water goes to the anode. + Anode oxidation - Cathode Reduction 2H 2 O+2e - → 2H 2 + 2OH - -0.41 v

48 2. Draw and completely analyze a 1.0 M KI electrolytic cell. Power Source - + Pt K+I-H2OK+I-H2O For oxidation the most spontaneous reaction is found on the redox chart and is lowest. + Anode oxidation - Cathode Reduction 2H 2 O+2e - → 2H 2 + 2OH - -0.41 v

49 Cl 2 + 2e- → 2Cl-1.36 v 1/2O 2 + 2H + (10 -7 M) + 2e - → H 2 0 0.82 v Oxidation of water I 2(s) + 2e - → 2I - 0.54 v Reduction of water 2H 2 O + 2e - → 2H 2 + 2OH - -0.42 v Zn 2+ + 2e - → Zn (s) -0.76 v K + + 1e - → K (s) -2.93 v

50 Cl 2 + 2e- → 2Cl-1.36 v 1/2O 2(g) + 2H + (10 -7 M) → H 2 0 0.82 v Oxidation of water I 2(s) + 2e - → 2I - 0.54 v Oxidation of I - Reduction of water 2H 2 O + 2e - → 2H 2 + 2OH - -0.42 v Zn 2+ + 2e - → Zn (s) -0.76 v K + + 1e - → K (s) -2.93 v

51 Cl 2 + 2e- → 2Cl - 1.36 v overpotential effect means water is here 1/2O 2 + 2H + (10 -7 M) → H 2 0 0.82 v Oxidation of water I 2(s) + 2e - → 2I - 0.54 v Oxidation of I - Reduction of water 2H 2 O + 2e - → 2H 2 + 2OH - -0.42 v Zn 2+ + 2e - → Zn (s) -0.76 v K + + 1e - → K (s) -2.93 v

52 Cl 2 + 2e- → 2Cl - 1.36 v overpotential effect means water is here 1/2O 2 + 2H + (10 -7 M) → H 2 0 0.82 v Oxidation of water I 2(s) + 2e - → 2I - 0.54 v Oxidation of I - pick strongest reducing agent- lower Reduction of water 2H 2 O + 2e - → 2H 2 + 2OH - -0.42 v Zn 2+ + 2e - → Zn (s) -0.76 v K + + 1e - → K (s) -2.93 v

53 2. Draw and completely analyze a 1.0 M KI electrolytic cell. Power Source - + Pt K+I-H2OK+I-H2O For oxidation the most spontaneous reaction is found on the redox chart and is lowest. + Anode Oxidation - Cathode Reduction 2H 2 O+2e - → 2H 2 + 2OH - -0.41 v

54 2. Draw and completely analyze a 1.0 M KI electrolytic cell. Power Source - + Pt K+I-H2OK+I-H2O For oxidation the most spontaneous reaction is found on the redox chart and is lowest. + Anode Oxidation 2I - → I 2(s) + 2e - -0.54 v - Cathode Reduction 2H 2 O+2e - → 2H 2 + 2OH - -0.41 v

55 2. Draw and completely analyze a 1.0 M KI electrolytic cell. Power Source - + Pt K+I-H2OK+I-H2O Write the overall reaction with the cell potential. + Anode Oxidation 2I - → I 2(s) + 2e - -0.54 v - Cathode Reduction 2H 2 O +2e - → 2H 2 + 2OH - -0.41 v

56 2. Draw and completely analyze a 1.0 M KI electrolytic cell. Power Source - + Pt K+I-H2OK+I-H2O Write the overall reaction with the cell potential. + Anode Oxidation 2I - → I 2(s) + 2e - -0.54 v - Cathode Reduction 2H 2 O+2e - → 2H 2 + 2OH - -0.41 v 2H 2 O+ 2I - → 2H 2 + I 2(s) + 2OH - E 0 = -0.95 v

57 2. Draw and completely analyze a 1.0 M KI electrolytic cell. Power Source - + Pt K+I-H2OK+I-H2O Write the overall reaction with the cell potential. + Anode Oxidation 2I - → I 2(s) + 2e - -0.54 v - Cathode Reduction 2H 2 O+2e - → H 2 + 2OH - - 0.41 v 2H 2 O+ 2I - → H 2 + I 2(s) + 2OH - E 0 = -0.95 v MTV = +0.95v e-e- e-e-


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