Electrochemical Cells

Electrochemical Cells • For this lesson you will need: • Activity series of metals (in reference packet) • Standard reduction potential table (handed out yesterday)

The Big Questions • What is an electrochemical cell? • What are anodes and cathodes? • What are salt bridges and why are they necessary? • How do we calculate cell potential?

Electrochemical Cells • Electrochemical Cell – device that produces voltage via redox rxn. • Red. agent and ox. agent split into compartments (half-cells). • Anode – site of oxidation. • Produces e-. • Cathode – site of reduction. • Consumes e-.

Electrochemical Cell • Salt bridge – maintains charge balance between half-cells. • Contains inert salt (usu. NaCl or KCl)

V Diagram Salt Bridge Half-Cells

V Zinc-Copper Cell • Which metal is more active? • Zn is more active. • Zn is oxidized (anode). • Active  Anode • Cu2+ is reduced (cathode) Zn Cu Zn2+ Cu2+

V Zn  Zn2+ + 2e- Cu2+ + 2e- Cu Eored = +0.34 V Eoox = +0.76 V Zinc-Copper Cell • Oxidation Half-Rxn: • Zn  Zn2+ + 2e- • Eoox = +0.76 V • Reduction Half-Rxn: • Cu2+ + 2e-  Cu • Eored = +0.34 V • Cell Potential = 1.10 V Zn Cu Zn2+ Cu2+

V Direction of Electron Movement Zn Cu Zn2+ Cu2+ Zn  Zn2+ + 2e- Cu2+ + 2e- Cu Eored = +0.34 V Eoox = +0.76 V Zinc-Copper Cell

V Al  Al3+ + 3e- Cu2+ + 2e- Cu Eored = +0.34 V Eoox = +1.66 V Aluminum-Copper Cell • Which metal is more active? • Al • Al is anode; Cu is cathode • Voltages: • Al half-cell: +1.66 V • Cu half-cell: +0.34 V • Cell potential: +2.00 V Al Cu Al3+ Cu2+

V Ag+ + e- Ag Cu  Cu2+ + 2e- Eoox = -0.34 V Eored = +0.80 V Copper-Silver Cell • Which metal is more active? • Cu • Cu is anode; Ag is cathode • Voltages: • Cu half-cell: -0.34 V • Ag half-cell: +0.80 V • Cell potential: +0.46 V Ag Cu Ag+ Cu2+

Electrochemical Cells