Oxidation and Reduction Reactions

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Oxidation and Reduction Reactions
Magda van Aardt University Senior
College Murray.thompson_at_adelaide.edu.au
Dr Tak Kee Department of Chemistry University of
Adelaide
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Oxidation and Reduction Reactions

• This material has been developed as a part of
  the Australian School Innovation in Science,
  Technology and Mathematics Project funded by the
  Australian Government Department of Education,
  Science and Training as a part of the Boosting
  Innovation in Science, Technology and Mathematics
  Teaching (BISTMT) Programme.

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Refraction and Optical Fibres

• When light travels from one medium to another it
  changes speed.
• It also changes direction.

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Oxidation and Reduction Redox Reactions
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Chemical reaction types
Redox reactions can be Single
replacement reaction Combination reactions
Decomposition Combustion reactions
Acid-base reactions double replacement
reactions
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Redox Reactions
Involve a transfer of electrons between
reacting species.
Takes place when reduction and oxidation occur
simultaneously
RED OX REDOX
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Redox reactions in batteries
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Redox reactions in lead acid batteries
h
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Redox reactions in photosynthesis
6H2O 6CO2 light energy ? C6H12O6 6O2
http//plantsandalgae/photography_091.jpeg
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Cell respiration
?
Energy ATP (adenosine triphosphate)



Glucose reductant
Carbon dioxide
Oxygenoxidant
water
Glucose
ATP
http//biology.clc.uc.edu/Courses/bio104/cellresp.
htm
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Photography
K2Cr2O7
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Electrolysis SALTS AND WATER
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Fuel Cells
Reduction at Cathode
Reduction half equation ½O2 (g) 2e- 2H ? H2O
Oxidation at the anode
Oxidation half equation H2 (g) ? 2H
2e-
http//p2library.nfesc.navy.mil/issues/emergeoct20
05/fuelcell.jpg
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Fuel Cells (cont)
Space Shuttle Discovery hurtles into space on
mission STS-105, August 10, 2001.
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Combustion
Complete Combustion of propane C3H8( g) O2
(g) ? 3CO2(g) 4H2O(g)
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Fireworks
http//www.chemsoc.org/ExemplarChem/entries/2004/i
cl_Gondhia/lightcolour.htmlComposition
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REDOX REACTIONS IN BLEACHES H2O2 HClO
SO2
http//commons.wikimedia.org/wiki/ImageBleach-bot
tle.jpg
HOCl (aq) is the active ingredient in White King
http//www.npr.org/templates/story/story.php?story
Id3892457
http//www.ultrasonic-stain-remover.com/blood_stai
n_remover.jpg er.com/blood_stain_remover.jpg
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Rusting / corrosion
Rust Fe2O3.H2O (the red brown flaky stuff)
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Steel making (cont)
Fe2O3 (S) CO (g) ? 2Fe (l) 3CO2
(g)
3
2
0
4
oxidation
reduction
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Steel making (cont)
Fe2O3 (s) 3CO (g) ? 2Fe (s)
3CO2
http//www.bbc.co.uk/history/interactive/animation
s/blast_furnace/index.shtml
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Galvanic Cells
Salt bridge Electrolyte Solution with ions to
carry charge KCl (aq) or NO3(aq)
ELECTROLYTES
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Electroplating
http//www.glenair.com/qwikconnect/vol7num4/electr
o.jpg
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Spin-Coating a simple way to produce thin films
Films of 100 nm can be routinely produced
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Organic Light Emitting Diode (OLED)
Voltage source V volts


Field line


Device material (Ru2)
Tris(2,2'-bipyridyl) Ruthenium(II)
Electron (in the form of Ru) and hole (Ru3)
migrate towards centre and recombine to produce
light A 3rd year Chem student practical at
Adelaide University
Positive charge or hole migration
Electron migration
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LESSON 2

• OXIDATION AND REDUCTION

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REDOX OXidation REDuction

• What is oxidation ?

What is reduction?
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What is oxidation?
OXIDATION IS DEFINED AS
1 LOSS OF HYDROGEN CH3 OH
Cr2O7 2- ? CH2O (methanol)
H (heat) (methanal)
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What is oxidation?
OXIDATION IS DEFINED AS
2 GAIN OF OXYGEN Mg(s) O2(g) ? 2MgO 2Ca (s)
O2(g) ? 2CaO
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What is oxidation?

• OXIDATION IS DEFINED AS

3LOSS OF ELECTRONS
OXIDATION
(LEO)
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What is oxidation?

• OXIDATION IS DEFINED AS

4 INCREASE IN OXIDATION NUMBER
Fe (s) ? Fe 2 (aq) 2e-
0
2
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What is reduction?

• REDUCTION IS DEFINED AS

1 GAIN OF HYDROGEN
C3H6 (g) H2(g) (catalyst) Ni ? C3H8(g)
(propene) heat pressure
(propane)

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What is reduction?
REDUCTION IS DEFINED AS
2 LOSS OF OXYGEN
CuO (s) H2(g) ? Cu (s) H2O (g)
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What is reduction?
REDUCTION IS DEFINED AS

• 3 GAIN OF ELECTRONS
• REDUCTION
• (GER)

O2(g) 4e- ? 2O2- (aq)
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What is reduction?
REDUCTION IS DEFINED AS
4 DECREASE IN OXIDATION NUMBER
Cl2 (g) 2e- ? 2Cl-(aq)
-1
0
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When is it a redox reaction ?

• What about this reduction reaction?
• 2MnO4-(aq) 16H 10e- ? Mn2(aq) 8H2O(l)
• and this one?
• Cr2O72-(aq) 14H 6e- ? 2Cr3(aq) 7H2O(l)

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Rules to determine oxidation numbers
Rule1
ELEMENTS

• uncombined with other
• elements their
• oxidation number is

ZERO
H2 Li N2 O3 S8 Fe Cu Mg Cl2 O2 F2
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Rules to determine oxidation numbers
RULE 2
SIMPLE IONS

• their oxidation number
• is the charge on the ion

H
1
Fe2
2
-2
O2-
Al 3
3
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Rules to determine oxidation numbers
RULE 3
OXYGEN IN COMPOUNDS IS 2
except in hydrogen peroxide (H2O2 )it is -1
compounds in which it is bounded to fluorine F2O
it is 2
MgSO4
K2CO3
SO2
CO
Na2O
P4O10
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Rules to determine oxidation numbers
RULE 2
MOLECULES
THE SUM OF THE OXIDATION NUMBERS IS
ZERO
What is the oxidation number of Phosphorus (P)
in P4 O10
4(Phosphorus s oxidation number which we
will take as x ) 10( oxidation number of
oxygen) 0
4 X
10 (-2) 0 4 X
20 X 5
X IV

YOU TRY S in SO3 and Cl in
HClO
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Rules to determine oxidation numbers
RULE 5
HYDROGEN
1 when in compound with a non metal
H2O WATER
NH4 AMMONIUM
NH3 AMMONIA
HCl HYDROCHLORIC ACID
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Rules to determine oxidation numbers
RULE 6
COMPLEX / POLYATOMIC IONS
THE SUM OF ALL THE OXIDATION NUMBERS IS
CHARGE ON THE ION
What is the oxidation number of S in SO42- ?
SO42-
(oxidation number of S is x)
x 4 (-2) -2
x -8 -2
x 8-2 x6
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Using oxidation numbers to identify a redox
reaction

• Is H2(g) I2(g) ? 2HI (g) a redox
  reaction?

0 Rule 1
1 Rule 5
The oxidation number of hydrogen changes from 0
to I Increase in oxidation number Hydrogen
has been oxidised (undergoes oxidation)
Hydrogen is the reductant (reducing agent)
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Using oxidation numbers to identify a redox
reaction
Is H2(g) I2(g) ? 2HI (g) a
redox reaction?

0 Rule 1
-1 Rule 4 and 5
The oxidation number of iodine changes from 0 to
I Decrease in oxidation number Iodine has
been reduced (undergoes reduction) Iodine acts
as the oxidant (oxidising agent)
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Using oxidation numbers to identify a redox
reaction
Is H2(g) I2(g) ? 2HI (g) a
redox reaction?

-1 Rule 45
0 Rule 1
1 Rule 5
0 Rule 1
Yes, oxidation number has changed for different
chemical species
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Using oxidation numbers to identify a redox
reaction

• Mg(s) H2SO4 (aq) ? MgSO4 (aq) H2 (g)

1 Rule 5
0 Rule 1
2
0
-2
6
-2
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The oxidation number of magnesium changes from 0
to 2 Increase in oxidation number Magnesium
metal has been oxidised (undergoes oxidation)
Magnesium metal (Mg) is the reductant (reducing
agent)
The oxidation number of H (in H2SO4 changes
from 1 to 0 (in H2) Decrease in oxidation
number H2SO4 has been reduced (undergoes
reduction) H2SO4 acts as the oxidant (oxidising
agent)