Voltaic Cells

1. Voltaic Cells web.fccj.org

2. Components of a Voltaic cell • consists of an electric cell that is made by placing conductors (electrodes) in conducting solutions (electrolytes) • A cell contains 2 half cells each with an electrode and electrolyte Positive electrode – cathode Negative electrode – anode Electrons move from anode to cathode This movement is called electricity

3. Components of a Voltaic cell • Connecting wire – makes the external circuit • Salt bridge or porous barrier – connects the two solutions without allowing mixing so that ions can move freely • Chemtoons • YouTube - Chemistry Music Video: Electrochemistry (You Start At The Anode)

4. Anode • Negative electrode • Electrons leave through the wire • Reducing agent is oxidized • Positive charge is produced in the electrolyte • Anions drift toward anode • Cations move away • Cathode • Positive electrode • Electrons enter through the wire • Oxidizing agent is reduced • Positive charge is removed from the electrolyte • Cations drift toward the electrode • Anions move away

5. As negative electrical charges (electrons) are carried away from the anode to the cathode through the external circuit, a current is produced. Ions moving through the porous barrier maintain electrical neutrality in the solutions. • voltaicCell Cell Notation Anode(-) / electolyte // electrolye / Cathode (+)

6. Cell Potential • The difference in electrical potential energy between the anode and the cathode in the cell (v) • Depends on the relative tendency of the reactants in the cell to lose and gain electrons • Independent of the size of the cell

7. standard cell: all entities in the half reactions are at SATP and at concentration of 1.0 mol/L • standard cell potential (Eo): the maximum electric potential difference of a standard cell. Difference per unit charge between the anode and the cathode. • standard reduction potential (Ero) is a relative measure of the tendency of an oxidizing agent to gain electrons (undergo reduction). The value may be reversed to obtain oxidation potentials. See redox table.

8. Values for the reduction potentials are assigned using hydrogen half cell as the reference half cell. • 2H+(aq) + 2e-  H2(g)Ero = 0.00 V • This half cell has been arbitrarily assigned a value of zero. • Reactions above are +, stronger oxidizing agents • Reactions below are -, and are stronger reducing agents

9. The standard cell potential is the sum of oxidation and reduction potentials in a cell • Eo = Ero – Ero or Eo = Eredo + Eoxo • If Eo is positive  spontaneous reaction • If Eo is negative  non spontaneous reaction Galvanic Cell with Zinc and Copper (You-tube) Galvanic Cell with Zinc and Copper