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Electrolysis of ionic compounds

Electrolysis of ionic compounds. Putting electrical energy in to force the nonspontaneous change. electrolysis. Opposite process to electrochemical (voltaic) cells Electrical energy is put into the reaction The nonspontaneous reactions occur

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Electrolysis of ionic compounds

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  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: Fe2+ + 2e-→ Fe • The anion (nonmetal ion) will be oxidized to neutral at the anode • Ex: 2 Cl-→ Cl2 + 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: 2H2O(l) + 2e-→ H2(g) + 2 OH-(aq) Eo = -0.83V • Water can be oxidized instead of the nonmetal ion at the anode: • Ex: 2H2O(l) → O2(g) + 4e- + 4 H+(aq) Eo = 1.23V

  5. In an aqueous solution of an ionic compound, the half reaction with the greater (more positive) reduction potential (Eo) will be reduced. • Ex: electrolysis of aqueous CoBr2 • Present and able to be reduced: Co2+, H2O Co2+ + 2e-→ Co Eo = -0.28V 2H2O(l) + 2e-→ H2(g) + 2 OH-(aq) Eo = -0.83V Co2+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 (Eo) will be reduced. • Ex: electrolysis of aqueous BaBr2 • Present and able to be reduced: Ba2+, H2O Ba2+ + 2e-→BaEo = -2.90V 2H2O(l) + 2e-→ H2(g) + 2 OH-(aq) Eo = -0.83V H2Owill be reduced instead of Ba2+

  7. In an aqueous solution of an ionic compound, the half reaction with the lower (more negative) reduction potential (Eo) will be oxidized. • Ex: electrolysis of aqueous CoBr2 • Present and able to be oxidized: Br1-, H2O 2 Br1- → Br2 + 2e-Eo = 1.07V 2H2O(l) → O2(g) + 4e- + 4 H+(aq) Eo = 1.23V Br1-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 (Eo) will be oxidized. • Ex: electrolysis of aqueous CoF2 • Present and able to be oxidized: F1-, H2O 2 F1- → F2 + 2e-Eo = 2.87V 2H2O(l) → O2(g) + 4e- + 4 H+(aq) Eo = 1.23V H2O will be oxidized instead of F1-

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