1. Oxidation and Reduction
Reactions that involve electron transfer
Batteries and chemistry

2. What do rust and the hydrogen fuel cell have in common?
Rusting is the oxidation of iron
The fuel cell functions by oxidation of hydrogen gas
Both involve transfer of electrons

3. Learning objectives Define oxidation and reduction process
Identify oxidation/reduction and oxidizing/reducing agents
Describe basic principles of an electrochemical cell
Decribe features of common battery types
Define units of electricity: volts and amps
Use potentials to predict progress of reactions

4. Oxidation-Reduction (Redox)
Oxidation is loss of electrons
Na → Na+ + e-
Reduction is gain of electrons
Cl + e- = Cl-

5. Other ways to view oxidation and reduction
The role of oxygen (oxidizing agent)
Oxidation is addition of O atoms
Fe + O2 → Fe2O3
Reduction is loss of O atoms
Fe2O3 +H2 → Fe + H2O
The role of hydrogen (reducing agent)
Oxidation is loss of H atoms
C2H5OH → CO2 + H2O
Reduction is gain of H atoms
C6H6 + H2 → C6H12

6. Redox with Zn and CuSO4 Zn metal reduces the Cu2+ ions to Cu metal
Zn loses electrons
Cu2+ gains electrons
Zn + CuSO4 = Cu + ZnSO4
Zn + Cu2+ = Zn2+ + Cu
Zn is oxidized
Cu2+ is reduced

7. Nuggets of redox processes
Where there is oxidation there is always reduction
Oxidizing agent
Reducing agent
Is itself reduced
Is itself oxidized
Gains electrons
Loses electrons
Causes oxidation
Causes reduction

8. Identifying oxidation and reduction: Follow the electrons
Only reactants (things on left) need to be considered
Metal elements:
Generally form positive ions (lose electrons)
Are reducing agents
Are oxidized
Nonmetal elements:
Form negative ions (gain electrons)
Are oxidizing agents
Are reduced

9. Redox in life Corrosion Combustion Disinfectants Antiseptics Bleaching
Fe + O2 → Fe2O3
Combustion
CH4 + O2 → CO2 + H2O
Disinfectants
Antiseptics
Bleaching
Cl + e- = Cl-

10. Biological systems Photosynthesis Energy + 6CO2 + 6H2O = C6H12O6 + 6O2
Respiration
C6H12O6 + 6O2 = 6CO2 + 6H2O + energy

11. Vitamin C and oxidation
Vitamins are organic compounds important for maintaining health
Vitamin C is also easily oxidized (it is a reducing agent)
Body produces free radicals which oxidize – aging, cancer, cardiovascular disease
Antioxidants (like vitamin C) defend against radicals
Question: should we take antioxidant supplements?

12. Energy and electricity
All chemical reactions involve energy change
Spontaneous reactions can provide energy in the form of electricity
Volta made the first battery (Voltaic cell)
Batteries involve electron transfer
Electron transfer involves oxidation/reduction

13. Daniell cell
Electrolytic cell that uses reduction of Cu2+ by Zn to produce voltage
In left beaker is Zn and Zn2+ ions
In right beaker is Cu and Cu2+ ions
“Salt bridge” completes the circuit:
Zn + Cu2+ = Zn2+ + Cu
Zn is oxidized (loses electrons)
Cu2+ is reduced (gains electrons)

14. Volts and amps
Volt measures potential – driving force – to move electrons. Voltage depends on type of chemical process and not on size of battery
Other types of potential:
Pressure moves air or liquids
Temperature moves heat
Chemical potential moves reactions
Amp is flow of charge (current). Size of current flowing depends on size of electrodes

15. Zn + 2MnO2 + H2O = Zn(OH)2 + Mn2O3
Your basic D cell
Oxidation
Zn = Zn2+ + 2e
Reduction
2MnO2 + H2O + 2e = Mn2O3 + 2OH-
Overall
Zn + 2MnO2 + H2O = Zn(OH)2 + Mn2O3

16. Lithium batteries
Lithium has a very large negative reduction potential
Li = Li+ + e….E = 3.04 V
The basis for light-weight, high energy density batteries
Low atomic mass of lithium
High reduction potential
Ability to make rechargeable batteries

17. Lead-acid batteries – a unique system
Lead battery technology is 100 years old
Provide high current required to crank engine instantly
Rechargeable
Inexpensive
Rugged
Oxidation
Pb + SO42- = PbSO4 + 2e
Reduction
PbO2 + SO H+ + 2e = PbSO4 + 2H2O
Overall
Pb + PbO2 + 2H2SO4 = 2PbSO4 + 2H2O
Discharge
Recharge

18. Fuel cells: There’s nothing new in chemistry
Grove’s “Gas Voltaic Battery” was the first fuel cell – in 1843

19. The modern gas voltaic battery
In a battery the “fuel” is sealed inside the cell
In a fuel cell it is supplied constantly from outside

20. The fuel cell advantage: tax-free conversion
Fuel cells convert chemical potential energy into electrical energy directly
Heat-tax free conversion
Intrinsically high efficiency

21. Fuel cell applications
Portable
Mobile
Stationary

22. Types of fuel cells All fuel cells are basically the same but:
What’s the fuel
Normally hydrogen
What’s the electrolyte
Transports H+ (or)
Transports O2-
Anode materials
Cathode materials
For an overview

23. SOFC Solid Oxide Fuel Cell All solid-state High efficiency
Electrolyte conducts O2- ions
Fuel can be varied
Requires high temperature ( ºC)