Electrochemistry (Oxidation/Reduction) CHEM 2124 – General Chemistry II Alfred State College Professor Bensley

Learning Objectives  Define oxidation-reduction reaction.  Learn the oxidation number rules and assign oxidation numbers.  Write the half-reactions of an oxidation- reduction reaction.  Determine the species undergoing oxidation and reduction.  Describe and construct basic galvanic cells  Calculate cell potential for basic galvanic cells

Oxidation and Reduction I.General Features II.Oxidation Numbers Assign oxidation numbers to Carbon in each of the following compounds: 1. Carbon Monoxide2. Carbon Dioxide 3. C 6 H 12 O 6 (Glucose)4. Sodium Bicarbonate For each of the following chemical reactions, determine whether or not the reaction is an example of an oxidation-reduction reaction. LiOH + HCN  H 2 O + LiCN LiCl + AgNO 3  AgCl + LiNO 3 P 4 (s) + 5O 2 (g)  P 4 O 10 (s) CuCl 2 (aq) + Al (s)  AlCl 3 (aq) + Cu (s)

Oxidation and Reduction III.Half Reactions What happens when copper wire is placed in a silver nitrate solution?

For each of the following Redox reactions, write the individual half-reactions. 1.Fe (s) + CuSO 4 (aq)  Cu (s) + FeSO 4 (aq) 2.Co (s) + Cl 2 (g)  CoCl 2 (g) In each of the following reactions, identify the oxidizing agent and the reducing agent. 1.Co (s) + Cl 2 (g)  CoCl 2 (g) 2.2Al (s) + 3F 2 (g)  2AlF 3 (s) 3.PbS (s) + 4H 2 O 2 (aq)  PbSO 4 (aq) + 4H 2 O (l)

Oxidation and Reduction 1.Combination Reactions 2.Decomposition Reactions 3.Displacement Reactions 4.Combustion Reactions IV. Examples of Oxidation–Reduction Reactions

Oxidation and Reduction V. Galvanic or voltaic cells

Anode Zn (s)  Zn 2+ (aq) + 2e - Cathode Cu 2+ (aq) + 2e -  Cu (s)

Oxidation and Reduction VI.Galvanic Cell Terminology A.Half cells B.Anode C.Cathode D.Salt Bridge E.Cell Notation F.Cell Potential E 0 (cell) = E 0 (red) – E 0 (ox)

Order the following oxidizing agents from weakest to strongest. Cu 2+ (aq), Fe 2+ (aq), Fe 3+ (aq) Order the following reducing agents from weakest to strongest. H 2 (g), Al (s), Cu (s)

Example Sketch the cell formed by Cd in Cd(NO 3 ) 2 and Ag in AgNO 3. Write the half-reactions, label the anode, cathode, salt bridge, and direction of electron flow. Write the cell notation. Calculate the overall cell potential for this cell.

VII. Biological Applications Respiration –Oxidation of glucose to CO 2 –Reduction of O 2 to H 2 O C 6 H 12 O 6 (s) + 6O 2 (g)  6CO 2 (g) + 6H 2 O (g) Photosynthesis –Oxidation of H 2 O to O 2 –Reduction of CO 2 to glucose –6CO 2 (g) + 6H 2 O (g) + light  C 6 H 12 O 6 + 6O 2 (g) Oxidation and Reduction