Oxidation and Reduction Reactions

Magda van AardtUniversity Senior CollegeMurray.thompson@adelaide.edu.au

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