Oxidation and Reduction Reactions Magda van Aardt University Senior College Dr Tak Kee Department of Chemistry University 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 : * 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

h Redox reactions in lead acid batteries

Redox reactions in photosynthesis 6H 2 O + 6CO 2 + light energy → C 6 H 12 O 6 + 6O 2

Cell respiration Cell respiration → Energy = ATP (adenosine triphosphate ) Glucose C 6 H 12 O 6 + 6O 2 → 6CO 2 +6H 2 O+ 30ATP energy +++ Glucose =reductant Oxygen= oxidant Carbon dioxide water ATP

Photography K 2 Cr 2 O 7

Electrolysisof water 2 H 2 O(l) → O 2 (g) + 2H 2 (g) Electrolysis: SALTS AND WATER

Oxidation half equation: H 2 (g) → 2H + + 2e - Reduction at Cathode Oxidation at the anode Fuel Cells Reduction half equation: ½O 2 (g) + 2e - + 2H + → H 2 O

Space Shuttle Discovery hurtles into space on mission STS-105, August 10, Fuel Cells (cont)

Complete Combustion of propane: C 3 H 8( g) + O 2 (g) → 3CO 2(g) + 4H 2 O(g) Combustion

Fireworks

bottle.jpg REDOX REACTIONS IN BLEACHES: H 2 O 2 HClO SO 2 REDOX REACTIONS IN BLEACHES: H 2 O 2 HClO SO 2 remover.com/blood_stain_remover.jpg er.com/blood_stain_remover.jpg storyId= HOCl (aq) is the active ingredient in White King

Rusting / corrosion Rust = Fe 2 O 3.H 2 O (the red brown flaky stuff)

reduction Fe 2 O 3 (S) + CO (g) → 2Fe (l) + 3CO 2 (g) oxidation Steel making (cont)

Fe 2 O 3 (s) + 3CO (g) → 2Fe (s) + 3CO 2

Galvanic Cells Salt bridge = Electrolyte = Solution with ions to carry charge KCl (aq) or NO 3(aq) ELECTROLYTES

Electroplating

Spin-Coating – a simple way to produce thin films Films of ~100 nm can be routinely produced

24 Tris(2,2'-bipyridyl) Ruthenium(II) +– Voltage source V volts +– Field line Positive charge or hole migration Electron migration Device material (Ru 2+ ) Organic Light Emitting Diode (OLED) Electron (in the form of Ru + ) and hole (Ru 3+ ) migrate towards centre and recombine to produce light – A 3 rd year Chem student practical at Adelaide University

LESSON 2 OXIDATION AND REDUCTION

REDOX = OXidation + REDuction What is oxidation ? What is reduction?

OXIDATION IS DEFINED AS : 1: LOSS OF HYDROGEN CH 3 OH Cr 2 O 7 2- → CH 2 O (methanol) H+ (heat) (methanal) What is oxidation?

OXIDATION IS DEFINED AS : 2: GAIN OF OXYGEN Mg (s) + O 2(g) → 2MgO 2Ca (s) + O 2(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 (s) → Fe 2+ (aq) + 2e What is oxidation?

REDUCTION IS DEFINED AS : 1: GAIN OF HYDROGEN C 3 H 6 (g) + H 2(g) (catalyst) Ni → C 3 H 8(g) (propene) heat pressure (propane) What is reduction?

2: LOSS OF OXYGEN CuO (s) + H 2(g) → Cu (s) + H 2 O (g) REDUCTION IS DEFINED AS : What is reduction?

3: GAIN OF ELECTRONS 3: GAIN OF ELECTRONS =REDUCTION =REDUCTION (GER) (GER) O 2(g) + 4e - → 2O 2- (aq) REDUCTION IS DEFINED AS : What is reduction?

4: DECREASE IN OXIDATION NUMBER Cl 2 (g) + 2e - → 2Cl - (aq) 0 REDUCTION IS DEFINED AS : What is reduction?

When is it a redox reaction ? What about this reduction reaction? What about this reduction reaction? 2MnO 4 - (aq) + 16H + +10e - → Mn 2+ (aq) + 8H 2 O (l) 2MnO 4 - (aq) + 16H + +10e - → Mn 2+ (aq) + 8H 2 O (l) and this one? and this one? Cr 2 O 7 2- (aq) + 14H + +6e - → 2Cr 3+ (aq) + 7H 2 O (l) Cr 2 O 7 2- (aq) + 14H + +6e - → 2Cr 3+ (aq) + 7H 2 O (l)

uncombined with other uncombined with other elements their elements their oxidation number is oxidation number is ELEMENTS: ZERO H 2 Li N 2 O 3 S 8 Fe Cu Mg Cl 2 O 2 F 2 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+H+ =+1Fe 2+ = +2 O 2- = -2 Al 3+ = +3 Rules to determine oxidation numbers

OXYGEN: IN COMPOUNDS IS –2 [except in hydrogen peroxide (H 2 O 2 )it is -1 compounds in which it is bounded to fluorine F 2 O it is +2 ] SO2SO2 Na 2 O COCO P 4 O 10 K2CO3K2CO3 MgSO 4 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 P 4 O 10 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 SO 3 … and Cl in HClO Rules to determine oxidation numbers RULE 2

HYDROGEN: = +1 when in compound with a non metal NH 3 AMMONIA H 2 O WATER HC l HYDROCHLORIC ACID NH 4 + 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 SO 4 2- ? (oxidation number of S is x) SO 4 2- x + 4 (-2) = -2 x -8 = -2 x= +8-2 x=+6 Rules to determine oxidation numbers RULE 6

Is H 2(g) + I 2(g) → 2HI (g) a redox reaction? Is H 2(g) + I 2(g) → 2HI (g) 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) 0 Rule 1 +1 Rule 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 H 2(g) + I 2(g) → 2HI (g) a redox reaction? Is H 2(g) + I 2(g) → 2HI (g) a redox reaction? Rule 4 and 5 0 Rule 1 Using oxidation numbers to identify a redox reaction

0 Rule 1 +1 Rule 5 Rule Rule 1 Is H 2(g) + I 2(g) → 2HI (g) a redox reaction? Is H 2(g) + I 2(g) → 2HI (g) a redox reaction? Yes, oxidation number has changed for different chemical species Using oxidation numbers to identify a redox reaction

2) Mg (s) + H 2 SO 4 (aq) → MgSO 4 (aq) + H 2 (g) 0 Rule 1 +1 Rule 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 H 2 SO 4 changes from +1 to 0 (in H 2 ) Decrease in oxidation number H 2 SO 4 has been reduced (undergoes reduction) H 2 SO 4 acts as the oxidant (oxidising agent) The oxidation number of H (in H 2 SO 4 changes from +1 to 0 (in H 2 ) Decrease in oxidation number H 2 SO 4 has been reduced (undergoes reduction) H 2 SO 4 acts as the oxidant (oxidising agent) Using oxidation numbers to identify a redox reaction