section 18.1 electron transfer reactions 1.to learn about metal-nonmetal oxidation–reduction...
TRANSCRIPT
Section 18.1
Electron Transfer Reactions
1. To learn about metal-nonmetal oxidation–reduction reactions
2. To learn to assign oxidation states
Objectives
Section 18.1
Electron Transfer Reactions
A. Oxidation-Reduction Reactions
• Oxidation-reduction reaction – a chemical reaction involving the transfer of electrons – Oxidation – loss of electrons – Reduction – gain of electrons
Section 18.1
Electron Transfer Reactions
A. Oxidation-Reduction Reactions
– Which element is oxidized? – Which element is reduced?
Section 18.1
Electron Transfer Reactions
B. Oxidation States
• Oxidation states – allow us to keep track of electrons in oxidation-reduction reactions
Section 18.1
Electron Transfer Reactions
B. Oxidation States
Section 18.2
Balancing Oxidation-Reduction Reactions
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 18.2
Balancing Oxidation-Reduction Reactions
A. 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)
Section 18.2
Balancing Oxidation-Reduction Reactions
A. Oxidation-Reduction Reactions Between Nonmetals
• C oxidized
– CH4 is the reducing agent.
• O2 reduced
– O2 is the oxidizing agent.
CH4(g) + 2O2(g) CO2(g) + 2H2O(g)
Section 18.2
Balancing Oxidation-Reduction Reactions B. Balancing Oxidation-Reduction Reactions by the Half-Reaction Method
• Half reaction – equation which has electrons as products or reactants
Section 18.2
Balancing Oxidation-Reduction Reactions B. Balancing Oxidation-Reduction Reactions by the Half-Reaction Method
Section 18.3
Electrochemistry and Its Applications
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 18.3
Electrochemistry and Its Applications
A. 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
Section 18.3
Electrochemistry and Its Applications
A. Electrochemistry: An Introduction
• Making an electrochemical cell
Section 18.3
Electrochemistry and Its Applications
A. 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.
Section 18.3
Electrochemistry and Its Applications
A. Electrochemistry: An Introduction
• A salt bridge or porous disk connects the half cells and allows ions to flow, completing the circuit.
Section 18.3
Electrochemistry and Its Applications
A. 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
Section 18.3
Electrochemistry and Its Applications
A. Electrochemistry: An Introduction
• Electrolysis – process where electrical energy is used to produce a chemical change
– Nonspontaneous
Section 18.3
Electrochemistry and Its Applications
B. Batteries
• Lead Storage Battery – Anode reaction - oxidationPb + H2SO4 PbSO4 + 2H+ + 2e
– Cathode reaction - reduction
PbO2 + H2SO4 + 2e + 2H+ PbSO4 + 2H2O
Section 18.3
Electrochemistry and Its Applications
B. Batteries
– Overall reaction
Pb + PbO2 + 2H2SO4 2PbSO4 + 2H2O
Section 18.3
Electrochemistry and Its Applications
B. Batteries
• Electric Potential – the “pressure” on electrons to flow from anode to cathode in a battery
Section 18.3
Electrochemistry and Its Applications
B. Batteries
• Dry Cell Batteries – do not contain a liquid electrolyte
– Acid version• Anode reaction - oxidation
Zn Zn2+ + 2e • Cathode reaction – reduction
2NH4+ + 2MnO2 + 2e
Mn2O3 + 2NH3 + 2H2O
Section 18.3
Electrochemistry and Its Applications
B. Batteries
• Dry Cell Batteries – do not contain a liquid electrolyte
– Alkaline version• Anode reaction - oxidation
Zn + 2OH ZnO + H2O + 2e
• Cathode reaction – reduction
2MnO2 + H2O + 2e Mn2O3 + 2OH
Section 18.3
Electrochemistry and Its Applications
B. 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
Section 18.3
Electrochemistry and Its Applications
C. Corrosion
• Corrosion 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
Section 18.3
Electrochemistry and Its Applications
D. Electrolysis
• Electrolysis – a process involving forcing a current through a cell to produce a chemical change that would not otherwise occur