Oxidation and Reduction Reactions
Magda van Aardt
Dr Tak Kee
University Senior College
Murray.thompson@adelaide.edu.au
Department of Chemistry
University of Adelaide
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.”
Refraction and Optical Fibres
• When light travels from one
medium to another it changes
speed.
• It also changes direction.
Oxidation and Reduction
Redox Reactions
Chemical reaction types
Acid-base reactions &
double replacement
reactions
Redox reactions can be :
* Single replacement reaction
* Combination reactions
* Decomposition
* Combustion reactions
Redox Reactions
Involve a transfer of electrons between
reacting species. …
Takes place when reduction and oxidation
occur simultaneously
RED + OX = REDOX
Redox reactions in batteries
Redox reactions in lead acid
batteries
h
Redox reactions in photosynthesis
6H2O + 6CO2
+ light energy →
http://plantsandalgae/photography_091.jpeg
C6H12O6 + 6O2
Cell respiration
C6H12O6 + 6O2 → 6CO2 + 6H2O + 30ATP
energy
→
Glucose
+
Oxygen=
=reductant
oxidant
Glucose
Carbon + water +
dioxide
Energy = ATP
(adenosine
triphosphate)
ATP
http://biology.clc.uc.edu/Courses/bio104/cellresp.htm
Photography
K2Cr2O7
Electrolysis: SALTS AND WATER
Electrolysis of water
2 H2O(l)
→
O2(g) + 2H2(g)
Fuel Cells
Reduction at Cathode
Reduction half equation:
½O2 (g)+ 2e- + 2H+ → H2O
Oxidation at the anode
Oxidation half equation:
H2 (g) → 2H+ + 2ehttp://p2library.nfesc.navy.mil/issues/emergeoct2005/fuelcell.jpg
Fuel Cells (cont)
Space Shuttle Discovery hurtles into space on mission
STS-105, August 10, 2001.
Combustion
Fireworks
http://www.chemsoc.org/ExemplarChem/entries/2004/icl_Gondhia/lightcolour.htmlComposition
REDOX REACTIONS IN
BLEACHES: H2O2 HClO SO2
http://commons.wikimedia.org/wiki/Image:Bleachbottle.jpg
HOCl (aq) is the active
ingredient in White King
http://www.ultrasonic-stainremover.com/blood_stain_remover.jpg
er.com/blood_stain_remover.jpg
http://www.npr.org/templates/story/story.php?
storyId=3892457
Rusting / corrosion
Rust = Fe2O3.H2O
(the red brown flaky stuff)
Steel making (cont)
Fe2O3
+3
(S)
+ CO (g) → 2Fe (l) + 3CO2 (g)
+2
reduction
0
+4
oxidation
Steel making (cont)
Fe2O3 (s)
+
3CO (g)
→ 2Fe (s)
+
3CO2
http://www.bbc.co.uk/history/interactive/animations/blast_furnace/index.shtml
Galvanic Cells
Salt bridge =
Electrolyte =
Solution with ions
to carry charge
KCl (aq) or NO3(aq)
ELECTROLYTES
Electroplating
http://www.glenair.com/qwikconnect/vol7num4/electro.jpg
Spin-Coating – a simple way
to produce thin films
Films of ~100 nm can be routinely produced
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
24
hole migration
Electron migration
LESSON 2
OXIDATION AND REDUCTION
REDOX =
OXidation + REDuction
What is oxidation ?
What is reduction?
What is oxidation?
OXIDATION IS DEFINED AS :
1: LOSS OF HYDROGEN
CH3 OH
Cr2O7 2-
(methanol)
H+ (heat)
→
CH2O
(methanal)
What is oxidation?
OXIDATION IS DEFINED AS :
2: GAIN OF OXYGEN
Mg(s) + O2(g) → 2MgO
2Ca (s) + O2(g) → 2CaO
What is oxidation?
OXIDATION IS DEFINED AS :
3:LOSS OF ELECTRONS
=OXIDATION
(LEO)
What is oxidation?
OXIDATION IS DEFINED AS :
4: INCREASE IN OXIDATION
NUMBER
Fe
0
(s)
→ Fe
+2
2+
(aq)
+ 2e-
What is reduction?
REDUCTION IS DEFINED AS :
1: GAIN OF HYDROGEN
C3H6 (g) + H2(g)
(propene)
(catalyst) Ni → C3H8(g)
heat pressure
(propane)
What is reduction?
REDUCTION IS DEFINED AS :
2: LOSS OF OXYGEN
CuO
(s)
+ H2(g) → Cu (s) + H2O (g)
What is reduction?
REDUCTION IS DEFINED AS :
3: GAIN OF ELECTRONS
=REDUCTION
(GER)
O2(g) + 4e- → 2O2-
(aq)
What is reduction?
REDUCTION IS DEFINED AS :
4: DECREASE IN OXIDATION
NUMBER
Cl2 (g) + 2e- → 2Cl-(aq)
0
-1
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)
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
Rules to determine oxidation
numbers
RULE 2
SIMPLE IONS:
their oxidation number
is the charge on the ion :
H+
=+1
Fe2+ = +2
O2- = -2
Al 3+ = +3
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 ]
SO2
MgSO4
K2CO3
CO
Na2O
P4O10
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
4X
4X
X
YOU TRY :
+ 10 (-2)
= 20
= +5
S in SO3…
= 0
X= +IV
and Cl in HClO
Rules to determine oxidation
numbers
RULE 5
HYDROGEN: = +1 when in compound
with a non metal
H2O
WATER
NH3
AMMONIA
NH4+
AMMONIUM
HCl
HYDROCHLORIC ACID
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- ?
(oxidation number of S is x)
SO42-
x + 4 (-2) = -2
x -8 = -2
x= +8-2
x=+6
Using oxidation numbers to
identify a redox reaction
Is H2(g) + I2(g) → 2HI (g) a redox reaction?
0
+1
Rule 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)
Using oxidation numbers to
identify a redox reaction
Is H2(g) + I2(g) → 2HI
0
Rule 1
(g)
a redox reaction?
-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)
Using oxidation numbers to
identify a redox reaction
Is H2(g) + I2(g) → 2HI
0
0
+1
Rule 1
Rule 1
Rule 5
(g)
a redox reaction?
-1
Rule
4+5
Yes, oxidation number
has changed for different
chemical species
Using oxidation numbers to identify
a redox reaction
2)
Mg(s) + H2SO4 (aq) → MgSO4 (aq) + H2 (g)
0
Rule 1
+1
Rule 5
+2
+6
-2
0
+6
-2
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)