2. Electrochemistry Voltaic Cells

3. Voltaic (Galvanic) Cells - spontaneous reaction used to produce electrical energy. Salt Bridge Cells Zn(s) + Cu 2+ (aq) → Zn 2+ (aq) + Cu(s) video

4. The salt bridge allows the current to flow but prevents contact between Zn and Cu 2+, which would short-circuit the cell. salt bridge demo

5. For the reaction: Zn (s) + 2H + (aq) → Zn 2+ (aq) + H 2 (g) use an inert Pt electrode for H + /H 2 half-cell. Bubble in H 2 over the Pt electrode. video

6. Standard Voltages E o = cell voltage when all species are at standard concentrations (1 atm for gases, 1M for solutions). Zn + 2 H + → Zn 2+ + H 2 E o = + 0.762 V = E ox (Zn) + E red (H + ) E red of H + is arbitrarily set to zero. Appendix E on page 1117 is a list of standard reduction potentials. The oxidation potential is obtained by changing the sign.

7. Ex Find the cell potential of the Zn - Cu cell.

8. The more positive the value of E red, the more easily reduced and the stronger the oxidizing agent. The more negative the value of E red, the more easily oxidized and the stronger the reducing agent. animation

9. Calculation of E o. E o = E ox + E red Cl 2(g) + 2 Br - (aq) → 2 Cl - (aq) + Br 2(l) E o = E red + E ox = E Cl 2 + E Br- = 1.360 V - 1.077 V = +0.283 V Since the calculated voltage is positive, this voltage can occur in a voltaic cell and the cell will produce electricity.

10. Ex - What, if anything, will happen when bromine is added to a solution of tin(II) chloride? If Br 2 is reduced, Sn 2+ cannot be Will give a negative E with Br 2

12. Notes Quiz https://docs.google.com/spreadsheet/embeddedform?formkey=dHFNTkFGU1pPUEpyZ0pq NnktWGVkYVE6MQ