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:Assign oxidation numbers to Carbon in each of the following compounds:

1. Carbon Monoxide1. Carbon Monoxide 2. Carbon Dioxide2. Carbon Dioxide

3. C3. C66HH1212OO6 6 (Glucose)(Glucose) 4. Sodium Bicarbonate4. 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 H2O + LiCN

LiCl + AgNO3 AgCl + LiNO3

P4 (s) + 5O2 (g) P4O10 (s)

CuCl2 (aq) + Al (s) AlCl3 (aq) + Cu (s)

Oxidation and Reduction

III. Half Reactions

What happens when copper wire is placed What happens when copper wire is placed in a silver nitrate solution? in a silver nitrate solution?

For each of the following Redox reactions, write the individual half-reactions.1. Fe (s) + CuSO4 (aq) Cu (s) + FeSO4 (aq)

2. Co (s) + Cl2 (g) CoCl2 (g)

In each of the following reactions, identify the oxidizing agent and the reducing agent.

1. Co (s) + Cl2 (g) CoCl2 (g)

2. 2Al (s) + 3F2 (g) 2AlF3 (s)

3. PbS (s) + 4H2O2 (aq) PbSO4 (aq) + 4H2O (l)

Oxidation and Reduction

1. Combination Reactions

2. Decomposition Reactions

3. Displacement Reactions

4. Combustion Reactions

IV. Examples of Oxidation–Reduction Reactions

Oxidation and ReductionOxidation and Reduction

V. Galvanic or voltaic cells

AnodeZn (s) Zn 2+ (aq) + 2e-

CathodeCu 2+ (aq) + 2e- Cu (s)

Oxidation and Reduction

VI. Galvanic Cell TerminologyA. Half cellsB. AnodeC. CathodeD. Salt BridgeE. Cell NotationF. Cell Potential

E0 (cell) = E0 (red) – E0 (ox)

Order the following oxidizing agents from weakest to strongest.

Cu2+ (aq), Fe2+ (aq), Fe3+ (aq)

Order the following reducing agents from weakest to strongest.

H2 (g), Al (s), Cu (s)

Example

• Sketch the cell formed by Cd in Cd(NO3)2 and Ag in AgNO3.

• 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 CO2

– Reduction of O2 to H2O

C6H12O6 (s) + 6O2 (g) 6CO2 (g) + 6H2O (g)

• Photosynthesis– Oxidation of H2O to O2

– Reduction of CO2 to glucose– 6CO2 (g) + 6H2O (g) + light C6H12O6 + 6O2 (g)

Oxidation and Reduction