Electrochemistry Oxidation-Reduction Dr. Ron Rusay Spring 2004 © Copyright 2004 R.J. Rusay

Oxidation-Reduction Oxidation is the loss of electrons. Reduction is the gain of electrons. The reactions occur together. One does not occur without the other. The terms are used relative to the change in the oxidation state of the reactant(s).

Oxidation Reduction Reactions

Oxidation State (Oxidation Number)

Cu 2+  Cu (s) H 2 (g)  2 H e- - 2 e- Use oxidation numbers to determine what is oxidized and what is reduced. Number of electrons gained must equal the number of electrons lost. - 2 e- +2 e-

A Voltaic Cell

Voltaic Cells

Voltages of Some Common Voltaic Cells Voltaic Cell Voltage (V) Common alkaline battery 1.5 Lead-acid car battery (6 cells = 12 V) 2.0 Calculator battery (mercury) 1.3 Electric eel (~ 5000 cells in 6-ft eel = 750 V) 0.15 Nerve of giant squid (across cell membrane) 0.070

Automotive Application: the Discharge and Recharging of a Lead-Acid Battery

Lithium Solid-State Battery Nickel-Cadmium (Nicad) Battery

How do teeth whiteners work?

Comparison of Voltaic and Electrolytic Cells Electrode Cell Type  G E cell Name Process Sign Voltaic 0 Anode Oxidation - Voltaic 0 Cathode Reduction + Electrolytic > 0 < 0 Anode Oxidation + Electrolytic > 0 < 0 Cathode Reduction -

Electrochemical Reactions

Electrolysis: Chrome Plating

Aluminum Production Using an Electrolytic Cell Do you recycle? It takes only 5% of the energy to produce a can from recycled aluminum vs. aluminum ore.

Hydrogen Fuel Cell

Flow Batteries (Fuel Cells) The Hydrogen Oxygen Fuel Cell Anode (oxidation): H 2 (g) + CO 3 2- (l) H 2 O (g) + CO 2 (g) + 2 e - Cathode (reduction): 1/2 O 2 (g) + CO 2 (g) + 2 e - CO 3 2- (l) Overall (cell) reaction: H 2 (g) + 1/2 O 2 (g) H 2 O (g) E cell = 1.2 V Other Fuel Cells: 2 NH 3 (g) + 3/2 O 2 (g) N 2 (g) + 3 H 2 O (l) N 2 H 4 (g) + O 2 (g) N 2 (g) + 2 H 2 O (l) CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O (l) Chemistry of Batteries Where doses the H 2 (g) come from?