oxidation and reduction reactions magda van aardt university senior college...
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Oxidation and Reduction Reactions
Magda van AardtUniversity Senior [email protected]
Dr Tak KeeDepartment of ChemistryUniversity of Adelaide
“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.”
Oxidation and Reduction Reactions
•When light travels from one medium to another it changes speed.
•It also changes direction.
Refraction and Optical Fibres
Oxidation and Reduction Redox Reactions
Chemical reaction types
Acid-base reactions & double replacement reactions
Redox reactions can be Redox reactions can be :: * Single replacement reaction* Single replacement reaction
* Combination reactions * Combination reactions
* Decomposition * Decomposition * Combustion reactions* 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
h
Redox reactions in lead acid batteries
Redox reactions in photosynthesis
http://plantsandalgae/photography_091.jpeg
6H2O + 6CO2
+ light energy →
C6H12O6 + 6O2
Cell respiration Cell respiration
→ Energy = ATP
(adenosine triphosphate
)Glucose
http://biology.clc.uc.edu/Courses/bio104/cellresp.htm
C6H12O6 + 6O2
→
6CO2 + 6H2O + 30ATPenergy
+ + +Glucose =reductant Oxygen
=oxidant
Carbon dioxide
water
ATP
Photography
K2Cr2O
7
Electrolysis of water
2 H2O(l) → O2(g) + 2H2(g)
Electrolysis: Electrolysis: SALTS AND WATER SALTS AND WATER
Oxidation half equation: H2 (g) → 2H+ + 2e-
http://p2library.nfesc.navy.mil/issues/emergeoct2005/fuelcell.jpg
Reduction at Cathode
Oxidation at the anode
Fuel Cells
Reduction half equation:½O2 (g)+ 2e- + 2H+ → H2O
Space Shuttle Discovery hurtles into space on missionSTS-105, August 10, 2001.
Fuel Cells (cont)
Complete Combustion of propane:
C3H8( g) + O2 (g) → 3CO2(g) + 4H2O(g)
Combustion
FireworksFireworks
http://www.chemsoc.org/ExemplarChem/entries/2004/icl_Gondhia/lightcolour.htmlComposition
http://commons.wikimedia.org/wiki/Image:Bleach-bottle.jpg
REDOX REACTIONS IN REDOX REACTIONS IN BLEACHES: BLEACHES: HH22OO22 HClOHClO SOSO22
http://www.ultrasonic-stain-remover.com/blood_stain_remover.jpger.com/blood_stain_remover.jpg
http://www.npr.org/templates/story/story.php?storyId=3892457
HOCl (aq) is the active ingredient in White King
Rusting / corrosion
Rust = Fe2O3.H2O (the red brown flaky stuff)
reduction
Fe2O3 (S) + CO (g) → 2Fe (l) + 3CO2 (g)
+3 +2 0 +4
oxidation
Steel making (cont)
Steel making (cont)
Fe2O3 (s) + 3CO (g) → 2Fe (s) + 3CO2
http://www.bbc.co.uk/history/interactive/animations/blast_furnace/index.shtml
Galvanic Cells Galvanic Cells
Salt bridge = Electrolyte = Solution with ions to carry charge KCl (aq) or NO3(aq)
ELECTROLYTES
http://www.glenair.com/qwikconnect/vol7num4/electro.jpg
Electroplating
Spin-Coating – a simple way to produce thin films
Films of ~100 nm can be routinely produced
2424
Tris(2,2'-bipyridyl) Ruthenium(II)
+ –
Voltage sourceV volts
+ –
Field line
Positive charge or hole migration
Electron migration
Device material (Ru2+)
Organic Light Emitting Diode (OLED)
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
LESSON 2 LESSON 2
OXIDATION AND REDUCTIONOXIDATION AND REDUCTION
REDOX = OXidation + REDuction
What is oxidation ?What is oxidation ?
What is What is reduction? reduction?
OXIDATION IS DEFINED AS :
1: LOSS OF HYDROGEN CH3 OH Cr2O7 2-
→ CH2O
(methanol) H+ (heat) (methanal)
What is oxidation?
OXIDATION IS DEFINED AS :
2: GAIN OF 2: GAIN OF OXYGENOXYGEN
MgMg(s) (s) + O+ O2(g) 2(g) → 2MgO→ 2MgO
2Ca 2Ca (s)(s) + + OO2(g) 2(g) → 2CaO→ 2CaO
What is oxidation?
OXIDATIONOXIDATION ISIS DEFINED AS :DEFINED AS :
3:LOSS OF ELECTRONS =OXIDATION (LEO)
What is oxidation?
OXIDATIONOXIDATION ISIS DEFINED AS :DEFINED AS :
4: INCREASE IN OXIDATION NUMBER
Fe (s) → Fe 2+ (aq) + 2e-
0 +2
What is oxidation?
REDUCTIONREDUCTION ISIS DEFINED AS :DEFINED AS :
1: GAIN OF HYDROGEN C3H6 (g) + H2(g) (catalyst) Ni → C3H8(g) (propene) heat pressure (propane)
What is reduction?
2: LOSS OF 2: LOSS OF OXYGENOXYGEN
CuO (s) + H2(g) → Cu (s) + H2O (g)
REDUCTIONREDUCTION ISIS DEFINED AS :DEFINED AS :
What is reduction?
3:3: GAIN OF ELECTRONS GAIN OF ELECTRONS
=REDUCTION=REDUCTION
(GER)(GER)
O2(g) + 4e- → 2O2- (aq)
REDUCTIONREDUCTION ISIS DEFINED AS :DEFINED AS :
What is reduction?
4: DECREASE IN OXIDATION NUMBER
Cl2 (g) + 2e- → 2Cl-(aq)
0 -1
REDUCTIONREDUCTION ISIS DEFINED AS :DEFINED AS :
What is reduction?
When is it a redox reaction ? When is it a redox reaction ?
What about this reduction reaction? What about this reduction reaction?
2MnO2MnO44--(aq)(aq)+ 16H+ 16H+ + +10e+10e-- → Mn → Mn2+2+
(aq)(aq)+ 8H+ 8H22OO(l)(l)
and this one?and this one?
CrCr22OO772-2-
(aq) (aq) ++ 14H14H++ +6e+6e- - → 2Cr→ 2Cr3+3+
(aq)(aq)+ 7H+ 7H22OO(l)(l)
uncombined with other uncombined with other elements their elements their oxidation number isoxidation number is
ELEMENTS:
ZERO
H2 Li N2 O3 S8 Fe Cu Mg Cl2 O2 F2
Rule1
Rules to determine oxidation numbers
SIMPLE IONS:
RULE 2
their oxidation number their oxidation number is the charge on the ion : is the charge on the ion :
H+
=+1 Fe2+ = +2
O2- = -2 Al 3+ = +3
Rules to determine oxidation numbers
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
Na2O CO
P4O10
K2CO3 MgSO4
Rules to determine oxidation numbers
RULE 3
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
Rules to determine oxidation numbers
RULE 2
HYDROGEN:
= +1 when in compound with a non metal
NH3
AMMONIA
H2OWATER
HClHYDROCHLORIC ACID
NH4+
AMMONIUM
Rules to determine oxidation numbers
RULE 5
COMPLEX / POLYATOMIC IONS:
CHARGE ON THE ION
THE SUM OF ALL THE OXIDATION
NUMBERS IS:
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
Rules to determine oxidation numbers
RULE 6
Is HIs H2(g) 2(g) + I+ I2(g) 2(g) → 2HI → 2HI (g) (g) a redox reaction?a redox reaction?
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)
0Rule 1
+1Rule 5
Using oxidation numbers to identify a redox reaction
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)
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)
Is HIs H2(g) 2(g) + I+ I2(g) 2(g) → 2HI → 2HI (g) (g) a redox reaction?a redox reaction?
-1 Rule 4 and 5
0Rule 1
Using oxidation numbers to identify a redox reaction
0Rule 1
+1Rule 5
-1 Rule 4+5
0Rule 1
Is HIs H2(g) 2(g) + I+ I2(g) 2(g) → 2HI → 2HI (g) (g) a redox a redox
reaction?reaction?
Yes, oxidation number has changed for different chemical species
Using oxidation numbers to identify a redox reaction
2)2) MgMg(s) (s) + H+ H22SOSO4 (aq) 4 (aq) → MgSO→ MgSO4 (aq) 4 (aq) + H+ H2 (g) 2 (g)
0 Rule 1
+1Rule
5+2
0 0
-2-2+6 +6
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)
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)
Using oxidation numbers to identify a redox reaction