Chapter 11 Oxidation (氧化 ) and
Reduction (还原 )
Acid-base reaction,Transfer of proton
Oxidation and reduction,transfer of electron
11.1 Oxidation is the loss of electrons and
reduction is the gain of electrons
? Oxidation is the process whereby a reactant
loses one or more electrons.
? Reduction is the opposite process whereby
a reactant gains one or more electrons.
? Oxidation and reduction are complementary
and simultaneous processes.
? 2Na + Cl2 2NaCl
? 2Na 2Na+ + 2e- Oxidation
? Cl2 + 2e- 2Cl- Reduction
? In this reaction,sodium is acting as a
reducing agent (还原剂 ),which is any
reactant that causes another reactant to be
reduced,Conversely,the chlorine causes
oxidation of the sodium and so it is acting
as an oxidizing agent （氧化剂）,
Fig 11.1 formation of sodium
chloride
Different elements have different
oxidation and reduction tendencies
Little
tendency
to lose or
gain
electronsTendency to gain
electrons
Tendency to lose
electrons
11.2 Photography works by selective oxidation and
reduction
11.3 The energy of flowing electrons can be
harnessed
? Electrochemistry (电
化学 ) is the study of
the relationship
between electrical
energy and
chemical change,
Use oxidation-
reduction reaction to
produce an electric
current or use an
electric current to
produce an
oxidation-reduction
reaction,Fig 11.7 the salt bridge completes the
electric circuit
? The electricity of a battery comes from oxidation-
reduction reactions
? A voltaic cell,which is an all-in-one,self-
contained unit,is called a battery,Batteries are
either disposable or rechargeable,
? Principle of batteries,Two materials that oxidize
and reduce each other are connected by a
medium through which ions travel to balance an
external flow of electrons.
Disposable batteries
ZnCl2 (ag) + 2NH3 (g) Zn(NH3)2Cl2 (s)
2MnO2 (s) + H2 (g) Mn2O3 (s) + H2O (l)
Electrode (电极 )
cathode (阳极 ),where chemicals are reduced.
Anode (阴极 ),where chemicals are oxidized.
Fig 11.8 a common
dry-cell battery with a
graphite rod
immersed in a paste
of ammonium
chloride,manganese
dioxide,and zinc
chloride
Reduction 2NH4++2e- 2NH3+H2
Oxidation Zn Zn2++2e-
Alkaline battery
Zn (s) + 2OH- (aq) ZnO (s) + H2O (l) +2 e- Oxidation
2MnO2 (s) + 2e- Mn2O3 (s) + 2OH- (aq) Reduction
Fig11.19 Alkaline batteries last a lot longer
than dry-cell batteries and give a steadier
voltage,but they are expensive
Rechargeable battery
engine
Oxidation Pb + SO42- ? PbSO4 + 2e
Reduction of elemental Pb to pb2+
Reduction PbO2 + SO4- + 4H+ + 2e ? PbSO4 + 2H2O
Oxidation of elemental pb4+ to pb2+
engine
alternator
Oxidation PbSO4 + 2e ? Pb + SO42-
Reduction of elemental Pb2+ to pb
Reduction PbSO pb4+ 4 + 2H2O ? PbO2 + SO4- + 4H+ + 2e
Oxidation of elemental pb2+ to pb4+
Fig 11.10 (a) electrical
energy from the battery
forces the starter motor
to start the engine,(b)
the combustion of fuel
keeps the engine
running and provides
energy to spin the
alternator,which
recharges the battery,
Note that the battery has
a reversed cathode-
anode orientation during
recharging
Fuel cells (燃料电池 ) are highly efficient sources of
electrical energy
Oxidation 2H2+4OH- 4H2O+4e- Reduction 4e-+O2+2H2O 4OH-
Porous graphite electrodes
Fig11.11 the
hydrogen-
oxygen fuel cell
Fig 11.12
because this bus
is powered by a
fuel cell,its tail
pipe emits
mostly water
vapor
Electrical energy can produce chemical change
? Electrolysis (电解 ) is
the use of electrical
energy to produce
chemical change.
Electrical energy + 2H2O 2H2 (g) + O2
Fig 11.14 the electrolysis of
water produces hydrogen gas
and oxygen gas in a 2:1ratio by
volume,which is in accordance
with the chemical formula for
water:H2O,For this process to
work,ions must be dissolved
in the water so that the
electricity can be conducted
between the electrodes
Oxidation 2AlOF32-+6F-+C 2AlF63-+CO2+4e-
Reduction AlF63-+3e- Al +6F-
Figure 11.15
The melting point of aluminum
oxide(2030℃ ) is too high for it
to be efficiently electrolyzed to
aluminum metal,When the
oxide is mixed with the mineral
cryolite,The melting point of the
oxide drops to a more
reasonable 980℃, A strong
electric current passed through
the molten aluminum oxide-
cryolite mixture generates
aluminum metal at the cathode,
where aluminum ions pich up
electrons and so are reduced to
elemental aluminum
Molten Al2O3+Na3AlF6 mixture
Power
source
cathode
11.4 Oxygen is responsible for corrosion and
combustion
? Iron to rust,4Fe + 3O2 +3H2O 2Fe2O3,3H2O
? A thin layer of protective layer was formed during the
oxidation of aluminum.
? Since aluminum has higher tendency to be oxidized,a
thin layer of aluminum on iron can protect iron from
corresion.
Cathodic protection
Electroplating
Figure 11.20
As electrons flow into the
hubcap and give it a negative
charge,positively charged
chromiun ions move from the
solution to the hubcap and are
reduced to chromium metal,
which deposits as a coating on
the hubcap,The solution is kept
supplied with ions as chromium
atoms in the cathode are
oxidized to Cr2+ ions
? Combustion is also an oxidation-reduction
reaction.
? Many well,designed” oxidation-reduction
reactions happen in our bodies.
Reduction (还原 )
Acid-base reaction,Transfer of proton
Oxidation and reduction,transfer of electron
11.1 Oxidation is the loss of electrons and
reduction is the gain of electrons
? Oxidation is the process whereby a reactant
loses one or more electrons.
? Reduction is the opposite process whereby
a reactant gains one or more electrons.
? Oxidation and reduction are complementary
and simultaneous processes.
? 2Na + Cl2 2NaCl
? 2Na 2Na+ + 2e- Oxidation
? Cl2 + 2e- 2Cl- Reduction
? In this reaction,sodium is acting as a
reducing agent (还原剂 ),which is any
reactant that causes another reactant to be
reduced,Conversely,the chlorine causes
oxidation of the sodium and so it is acting
as an oxidizing agent （氧化剂）,
Fig 11.1 formation of sodium
chloride
Different elements have different
oxidation and reduction tendencies
Little
tendency
to lose or
gain
electronsTendency to gain
electrons
Tendency to lose
electrons
11.2 Photography works by selective oxidation and
reduction
11.3 The energy of flowing electrons can be
harnessed
? Electrochemistry (电
化学 ) is the study of
the relationship
between electrical
energy and
chemical change,
Use oxidation-
reduction reaction to
produce an electric
current or use an
electric current to
produce an
oxidation-reduction
reaction,Fig 11.7 the salt bridge completes the
electric circuit
? The electricity of a battery comes from oxidation-
reduction reactions
? A voltaic cell,which is an all-in-one,self-
contained unit,is called a battery,Batteries are
either disposable or rechargeable,
? Principle of batteries,Two materials that oxidize
and reduce each other are connected by a
medium through which ions travel to balance an
external flow of electrons.
Disposable batteries
ZnCl2 (ag) + 2NH3 (g) Zn(NH3)2Cl2 (s)
2MnO2 (s) + H2 (g) Mn2O3 (s) + H2O (l)
Electrode (电极 )
cathode (阳极 ),where chemicals are reduced.
Anode (阴极 ),where chemicals are oxidized.
Fig 11.8 a common
dry-cell battery with a
graphite rod
immersed in a paste
of ammonium
chloride,manganese
dioxide,and zinc
chloride
Reduction 2NH4++2e- 2NH3+H2
Oxidation Zn Zn2++2e-
Alkaline battery
Zn (s) + 2OH- (aq) ZnO (s) + H2O (l) +2 e- Oxidation
2MnO2 (s) + 2e- Mn2O3 (s) + 2OH- (aq) Reduction
Fig11.19 Alkaline batteries last a lot longer
than dry-cell batteries and give a steadier
voltage,but they are expensive
Rechargeable battery
engine
Oxidation Pb + SO42- ? PbSO4 + 2e
Reduction of elemental Pb to pb2+
Reduction PbO2 + SO4- + 4H+ + 2e ? PbSO4 + 2H2O
Oxidation of elemental pb4+ to pb2+
engine
alternator
Oxidation PbSO4 + 2e ? Pb + SO42-
Reduction of elemental Pb2+ to pb
Reduction PbSO pb4+ 4 + 2H2O ? PbO2 + SO4- + 4H+ + 2e
Oxidation of elemental pb2+ to pb4+
Fig 11.10 (a) electrical
energy from the battery
forces the starter motor
to start the engine,(b)
the combustion of fuel
keeps the engine
running and provides
energy to spin the
alternator,which
recharges the battery,
Note that the battery has
a reversed cathode-
anode orientation during
recharging
Fuel cells (燃料电池 ) are highly efficient sources of
electrical energy
Oxidation 2H2+4OH- 4H2O+4e- Reduction 4e-+O2+2H2O 4OH-
Porous graphite electrodes
Fig11.11 the
hydrogen-
oxygen fuel cell
Fig 11.12
because this bus
is powered by a
fuel cell,its tail
pipe emits
mostly water
vapor
Electrical energy can produce chemical change
? Electrolysis (电解 ) is
the use of electrical
energy to produce
chemical change.
Electrical energy + 2H2O 2H2 (g) + O2
Fig 11.14 the electrolysis of
water produces hydrogen gas
and oxygen gas in a 2:1ratio by
volume,which is in accordance
with the chemical formula for
water:H2O,For this process to
work,ions must be dissolved
in the water so that the
electricity can be conducted
between the electrodes
Oxidation 2AlOF32-+6F-+C 2AlF63-+CO2+4e-
Reduction AlF63-+3e- Al +6F-
Figure 11.15
The melting point of aluminum
oxide(2030℃ ) is too high for it
to be efficiently electrolyzed to
aluminum metal,When the
oxide is mixed with the mineral
cryolite,The melting point of the
oxide drops to a more
reasonable 980℃, A strong
electric current passed through
the molten aluminum oxide-
cryolite mixture generates
aluminum metal at the cathode,
where aluminum ions pich up
electrons and so are reduced to
elemental aluminum
Molten Al2O3+Na3AlF6 mixture
Power
source
cathode
11.4 Oxygen is responsible for corrosion and
combustion
? Iron to rust,4Fe + 3O2 +3H2O 2Fe2O3,3H2O
? A thin layer of protective layer was formed during the
oxidation of aluminum.
? Since aluminum has higher tendency to be oxidized,a
thin layer of aluminum on iron can protect iron from
corresion.
Cathodic protection
Electroplating
Figure 11.20
As electrons flow into the
hubcap and give it a negative
charge,positively charged
chromiun ions move from the
solution to the hubcap and are
reduced to chromium metal,
which deposits as a coating on
the hubcap,The solution is kept
supplied with ions as chromium
atoms in the cathode are
oxidized to Cr2+ ions
? Combustion is also an oxidation-reduction
reaction.
? Many well,designed” oxidation-reduction
reactions happen in our bodies.
