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Electrolysis of ionic compounds Putting electrical energy in to force the nonspontaneous change.

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Presentation on theme: "Electrolysis of ionic compounds Putting electrical energy in to force the nonspontaneous change."— Presentation transcript:

1 Electrolysis of ionic compounds Putting electrical energy in to force the nonspontaneous change

2 electrolysis Opposite process to electrochemical (voltaic) cells Electrical energy is put into the reaction The nonspontaneous reactions occur Useful industrial process for the production of “reduced metals” electroplating

3 Molten ionic compounds Molten = melted (NOT dissolved!) Only species present are the cation and anion The cation (metal ion) will be reduced into a neutral metal atom at the cathode – Ex: Fe e - → Fe The anion (nonmetal ion) will be oxidized to neutral at the anode – Ex: 2 Cl - → Cl 2 + 2e -

4 Aqueous ionic compounds Besides the cation and anion, water is present as well Water can be reduced instead of the metal ion at the cathode: – Ex: 2H 2 O (l) + 2e - → H 2(g) + 2 OH - (aq) E o = -0.83V Water can be oxidized instead of the nonmetal ion at the anode: – Ex: 2H 2 O (l) → O 2(g) + 4e H + (aq) E o = 1.23V

5 In an aqueous solution of an ionic compound, the half reaction with the greater (more positive) reduction potential (E o ) will be reduced. Ex: electrolysis of aqueous CoBr 2 Present and able to be reduced: Co 2+, H 2 O Co e - → Co E o = -0.28V 2H 2 O (l) + 2e - → H 2(g) + 2 OH - (aq) E o = -0.83V Co 2+ will be reduced instead of water

6 In an aqueous solution of an ionic compound, the half reaction with the greater (more positive) reduction potential (E o ) will be reduced. Ex: electrolysis of aqueous BaBr 2 Present and able to be reduced: Ba 2+, H 2 O Ba e - → Ba E o = -2.90V 2H 2 O (l) + 2e - → H 2(g) + 2 OH - (aq) E o = -0.83V H 2 O will be reduced instead of Ba 2+

7 In an aqueous solution of an ionic compound, the half reaction with the lower (more negative) reduction potential (E o ) will be oxidized. Ex: electrolysis of aqueous CoBr 2 Present and able to be oxidized: Br 1-, H 2 O 2 Br 1- → Br 2 + 2e - E o = 1.07V 2H 2 O (l) → O 2(g) + 4e H + (aq) E o = 1.23V Br 1- will be oxidized instead of water

8 In an aqueous solution of an ionic compound, the half reaction with the lower (more negative) reduction potential (E o ) will be oxidized. Ex: electrolysis of aqueous CoF 2 Present and able to be oxidized: F 1-, H 2 O 2 F 1- → F 2 + 2e - E o = 2.87V 2H 2 O (l) → O 2(g) + 4e H + (aq) E o = 1.23V H 2 O will be oxidized instead of F 1-


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