Oxidation Reduction

Unit 18Section 1 – Electron Transfer Reactions

Section 2 – Balancing Oxidation Reduction Reactions

Section 3 – Electrochemistry and its Applications

Oxidation Reduction

1. To learn about metal-nonmetal oxidation–reduction reactions

2. To learn to assign oxidation states

Objectives Section 1 – Electron Transfer Reactions

Oxidation Reduction

Oxidation-Reduction Reactions Oxidation-reduction reaction – a chemical

reaction involving the transfer of electrons Oxidation – loss of electrons Reduction – gain of electrons

Oxidation Reduction

Oxidation-Reduction Reactions

Which element is oxidized? Which element is reduced?

Oxidation Reduction

Oxidation States Oxidation states – allow us to keep track of

electrons in oxidation-reduction reactions

Oxidation Reduction

Oxidation States

Oxidation Reduction

1. To understand oxidation and reduction in terms of oxidation states

2. To learn to identify oxidizing and reducing agents 3. To learn to balance oxidation-reduction equations

using half reactions

Objectives Section 2 – Balancing Oxidation Reduction Reactions

Oxidation Reduction

Oxidation-Reduction Reactions Between Nonmetals

Na oxidized Na is also called the reducing agent (electron donor).

Cl2 reduced Cl2 is also called the oxidizing agent (electron acceptor).

2Na(s) + Cl2(g) 2NaCl(s)

Oxidation Reduction

Oxidation-Reduction Reactions Between Nonmetals

C oxidized CH4 is the reducing agent.

O2 reduced O2 is the oxidizing agent.

CH4(g) + 2O

2(g) CO

2(g) + 2H

2O(g)

Oxidation Reduction

Balancing Oxidation-Reduction Reactions by the Half-Reaction Method

Half reaction – equation which has electrons as products or reactants

Oxidation Reduction

Balancing Oxidation-Reduction Reactions by the Half-Reaction Method

Oxidation Reduction

1. To understand the concept of electrochemistry 2. To learn to identify the components of an

electrochemical (galvanic) cell 3. To learn about commonly used batteries 4. To understand corrosion and ways of preventing it 5. To understand electrolysis 6. To learn about the commercial preparation of

aluminum

Objectives Section 3 – Electrochemistry and its Applications

Oxidation Reduction

Electrochemistry: An Introduction Electrochemistry – the study of the interchange of

chemical and electrical energy Two types of processes

Production of an electric current from a chemical reaction The use of electric current to produce chemical change

Oxidation Reduction

Electrochemistry: An Introduction Making an electrochemical cell

Oxidation Reduction

Electrochemistry: An Introduction

If electrons flow through the wire charge builds up.

• Solutions must be connected to permit

ions to flow to balance the charge.

Oxidation Reduction

Electrochemistry: An Introduction A salt bridge or porous disk connects the half cells

and allows ions to flow, completing the circuit.

Oxidation Reduction

Electrochemistry: An Introduction Electrochemical battery (galvanic cell) – device

powered by an oxidation-reduction reaction where chemical energy is converted to electrical energy

• Anode – electrode where

oxidation occurs

• Cathode – electrode where

reduction occurs

Oxidation Reduction

Electrochemistry: An Introduction Electrolysis – process where electrical energy is

used to produce a chemical change – Nonspontaneous

Oxidation Reduction

Batteries Lead Storage Battery

Anode reaction - oxidationPb + H

2SO

4 PbSO

4 + 2H+ + 2e

– Cathode reaction - reduction

PbO2

+ H2

SO4

+ 2e + 2H+ PbSO4

+ 2H2

O

Oxidation Reduction

Batteries– Overall reaction

Pb + PbO2

+ 2H2

SO4

2PbSO4

+ 2H2

O

Oxidation Reduction

Batteries Electric Potential – the “pressure” on electrons

to flow from anode to cathode in a battery

Oxidation Reduction

Batteries Dry Cell Batteries – do not contain a liquid electrolyte

– Acid version

• Anode reaction - oxidation

Zn Zn2+ + 2e

• Cathode reaction – reduction

2NH4+ + 2MnO

2 + 2e Mn

2O

3 + 2NH

3 + 2H

2O

Oxidation Reduction

Batteries Dry Cell Batteries – do not contain a liquid electrolyte

– Alkaline version

• Anode reaction - oxidation

Zn + 2OH ZnO + H2

O + 2e

• Cathode reaction – reduction

2MnO2 + H

2O + 2e Mn

2O

3 + 2OH

Oxidation Reduction

Batteries Dry Cell Batteries – do not contain a liquid electrolyte

– Other types

• Nickel-cadmium – rechargeable

• Silver cell – Zn anode, Ag2O cathode

• Mercury cell – Zn anode, HgO cathode

Oxidation Reduction

CorrosionCorrosion is the oxidation of metals to form

mainly oxides and sulfides.Some metals, such as aluminum, protect

themselves with their oxide coating. Corrosion of iron can be prevented by

coatings, by alloying and cathodic protection.

Cathodic protection of an

underground pipe

Oxidation Reduction

Electrolysis Electrolysis – a process involving forcing a

current through a cell to produce a chemical change that would not otherwise occur