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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