ib chemistry on redox, oxidizing, reducing agents and writing half redox equations

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Prepared by Lawrence Kok

Tutorial on Redox, Reducing, Oxidizing Agent and redox half equations

Redox - Oxidation state change- Electron transfer

Zn + CuSO4 → ZnSO4 + Cu Zn + CI2 → ZnCI2 No gain/loss oxygen/hydrogen

Are these redox rxns?

Yes – change in oxidation numberYes – loss/gain of electron

Yes – change in oxidation numberYes – loss/gain of electron✓ ✓

• Assuming bond are ionic with diff EN values (unless bet same element)• Assign each atom, measure of electron control relative to atom in pure element• Apparent/imaginary charge it has when bonded to diff elements• Unequal sharing electron based on electronegativity• + means lose electron• - means gain electron

Oxidation State/Number/ON Rules

Oxidation Reduction

Gain oxygen ↑ Loss oxygen ↓

Gain oxidation Number ↑

Loss oxidation Number ↓

Loss hydrogen ↓ Gain hydrogen ↑

Loss electron ↓ Gain electron ↑

H CIxx

xx

•x

∂-∂+

+1 -1Oxidation number

Oxidation state (sign, number) +2 NOT 2+

Oxidation state and formal charge useful tool for electron book- keeping. They are not REAL!- Oxidation state -Assume bond ionic with diff EN values (unless bet same element)- Formal charge – Assume bond covalent

Redox (Oxidation and Reduction)


• Assuming bond are ionic with diffEN values (unless bet same element)• Assign each atom, measure of electron control relative to atom in pure element• Apparent/imaginary charge it has when bonded to diff elements• Unequal sharing electron based on electronegativity• + means lose electron• - means gain electron

Oxidation Number/ON Rules

H CIxx

xx

•x

∂-∂+

+1 -1Oxidation number

Oxidation state (sign, number) +2 NOT 2+

Oxidation state and formal charge useful tool for electron book- keeping. They are not REAL!- Oxidation state -Assume bond ionic with diff EN values (unless bet same element)- Formal charge – Assume bond covalent

xx

CI CI


H CI Na CI

Imagine electron move to more EN element

O C O

oo

oo

xxoo

oo xx

xxox

Equal sharing

xx

xx

xx

ox

+1 -1Unequal sharing

0 0

xx xx

xx

ox

+1 -1Complete transfer

oxox

oo

oo

oo

oo

oo

oo

xoxo

Unequal sharing

-2 +4 -2

H O H

CI2 H CI Na CI C O2

+1 -1 -1+1 +4 -2

oo

ox

ox

+1 -2 +1Unequal sharing

H N HH

ox

ox

o x

oo

+1 -3 +1

+1

Unequal sharing

H2 O N H3

H C H

H

H

o xo x

ox

ox

+1

+1

+1

+1 -4

C H4

+1 -2 -3 +1 -4 +1

CI C CI

CI

CI

-1

-1

-1

-1

xx

xx

xx

xx

xx xx

xx

xx

xx

xx

xx

xx

xo

xo

ox

ox

+4

C CI4

+4 -1

0

Exceptions

Element ON Exception Example

Hydrogen +1 H +1

-1 Bond to metalMetal hydride

NaHCaH2

Oxidation Number/States/ON Rules Imagine electron move to more EN element

• Assuming bond are ionic with diff EN values (unless bet same element)• Assign each atom, measure of electron control relative to atom in pure element• Apparent/imaginary charge it has when bonded to diff elements• Unequal sharing electron based on electronegativity

H CI

xx

∂-xx

•x

Oxidation number +1 -1

∂+

xx

H CIxx

xx

xx

+1 -1

ox

Unequal sharing

H CI+1 -1

Na Hox

+1 -1Complete transfer

Na H+1 -1

Exceptions


Oxygen -2 O -2

+2Bond to fluorine

F2O

Exceptions


Oxygen -2 O -2

-1Peroxide

(O-O)H2O2

H O H F O Foo

oo

ox

ox

+1 -2 +1Unequal sharing

H2 O+1 -2

oo

oo

xx

xx

xx

xx

xx

xxo x

o x

-1 +2 -1Unequal sharing

F2 O-1 +2

O O HH

O-O single bond

oo

oo

oo

oo

o x

o xoo

equal sharing

+1 -1 -1 +1Unequal sharing

H2 O2

+1 -1

EN fluorine higher ↑EN oxygen higher ↑

Oxidation Number/ON Rules Imagine electron move to more EN element

O O H O HOxidation state O different – depend element bond with – different EN values !

F O F O Oxx

xx

xx

xx

xxxx

Equal sharing

0 0

O20

oo

oo

oo

oo

o x

o x+1 -2 +1

Unequal sharing

H2 O+1 -2

xx xx

xx xx

xxxx

o x

o x

-1 +2 -1

F2 O-1 +2

H Hoo

oo

oo

oo

oo

o x

o x

+1 -1 -1 +1

H2 O2+1 -1

Unequal sharing Unequal sharing


• Assuming bond are ionic with diff EN values (unless bet same element)• Assign each atom, measure of electron control relative to atom in pure element• Apparent/imaginary charge it has when bonded to diff elements• Unequal sharing electron based on electronegativity

H CI

xx

∂-xx

•x

Oxidation number +1 -1

∂+

xx


O O H O HOxidation state O different – depend element bond with – different EN values !

F O F O Oxx

xx

xx

xx

xxxx

Equal sharing

0 0

O2

0

oo

oo

oo

oo

o x

o x

+1 -2 +1

Unequal sharing

H2 O+1 -2

xx xx

xx xx

xxxx

o x

o x

-1 +2 -1

F2 O-1 +2

H Hoo

oo

oo

oo

oo

o x

o x

+1 -1 -1 +1

H2 O2+1 -1

Unequal sharing Unequal sharing


Oxidation state N different – depend element bond with – different EN values !

H N HH

HH O N O H O N O N O N

O

O O

O

o x

o x

o x

x xx x

+1 -3 +1

+1

-2

[N H4 ]-3 +1 +1

Unequal sharing

xx

o x

o x xoxo

xx

oo

oo oo

oo

+1 -2 +3 -2

Unequal sharing

H N O2

+1 +3 -2

O

o x

o x xoxo

xx

oooo

oo

+1 -2 +5 -2

-2

Unequal sharing

H N O3

+1 +5 -2

o x

o x

xxoo

xxoo

oo

oo

oo

oo

oo

oo

oo

oo

oo oo -2

-2 -2

-5 -5-2

N2 O5

Unequal sharing

-5 +2

+1+


Atoms uncombined free element state = ON = 0

Ion form – ON same as charged on ion

1

2

Mg

Mg2+

Na

Na+

O2 S8

O2-

3 ON for element same as its most common ion/groupON metal from Gp 1 – 3ON non metal Gp 5 - 7

Anion/Non metal

Gp 5 Gp 6 Gp 7

Oxidation state

Oxidation state

Oxidation state

- 3 - 2 - 1

N 3- O 2- F 1-

P 3- S 2- CI 1-

Cation/Metal

Gp 1 Gp 2 Gp 3

Oxidation state

Oxidation state

Oxidation state

+1 +2 +3

Na 1+ Mg 2+ Al 3+

K 1+ Ca 2+ Ga 3+

4

CI20 0 0 0 0

+1 +2 -2 -1 -2

CI- S2-

ON for transition metal varies Transition metal ions

Transition metals ions (variable oxidation states)

Sc+3

Ti+2+3

V+2+3

Cr+2+3+6

Mn+2+3+6+7

Fe+2+3

Co+2+3

Ni+2

Cu+1+2

Zn+2

Sc 3+ Ti 2+

Ti 3+

V 2+

V 3+

Cr 2+

Cr 3+

Cr 6+

Mn 2+

Mn 3+

Mn 6+

Mn 7+

Fe 2+

Fe 3+

Co 2+

Co 3+

Ni 2+ Cu 1+

Cu 2+

Zn 2+

Oxidation number

Diff ONCharge on ion

Click here on oxidation rulesClick here view simple step

Notes

Sc3+

Charge on Sc

Oxidation number

+3

Oxidation state

-+3+

ON all atoms in polyatomic ion add up to charge of polyatomic ion

ON all atoms in neutral molecule add up to 0

CO3 2- SO4

2-

H2SO4 CO25


HNO3

(+1)2 + (+6) + (-2)4 = 0

+1 +6 -2

(+4) + (-2)2 = 0 (+1) + (+5) + (-2)3 = 0

+4 -2 +1 +5 -2

(+4) + (-2)3 = -2

+4 -2

(+6) + (-2)4 = -2

NO31-

+6 -2

(+5) + (-2)3 = -1

+5 -2

7 ON atom/molecule of element = 0 (NOT combined)

H2 CI2 O2 Fe Cu Mg0 0 0 0 0 0

8 Monoatomic ion – ON same as charged on ion

Ionic compound

Charge ion Oxidation number

MgF2 Mg 2+ F 1- Mg (+2) F (-1)

NaCI Na 1+ CI 1- Na (+1) CI (-1)

KBr K 1+ Br 1- K (+1) Br (-1)

CaI2 Ca 2+ I 1- Ca (+2) I (-1)

Li3N Li 1+ N 3- Li (+1) N (-3)

Al2O3 Al 3+ O 2- AI (+3) O (-2)

9Formula compound

Charge Oxidation number

Name using oxidation number

FeO Fe 2+ or 2+ +2 Iron (II) oxide

Fe2O3 Fe 3+ or 3+ +3 Iron (III) oxide

Cu2O Cu 1+ or 1+ +1 Copper (I) oxide

CuO Cu 2+ or 2+ +2 Copper (II) oxide

MnO2 Mn 4+ or 4+ +4 Manganese (IV) oxide

MnO4- Mn 7+ or 7+ +7 Manganese (VII) oxide

K2Cr2O7 Cr 6+ or 6+ +6 Potassium dichromate (VI)

Cr2O3 Cr 3+ or 3+ +3 Chromium (III) oxide

Click here view chemguide notes

6


9 Metal more than one oxidation states, Roman numeral used

Manganese ChromiumIonic

compoundMnSO4 MnO2 K2MnO4 KMnO4 K2Cr2O7 Cr2O3

OxidationNumber

(+2) + (+6) + (-2)4 = 0 Mn (+2)

(+4) + (-2)2 = 0Mn (+4)

(+1)2 + (+6) + (-2)4 = 0Mn (+6)

(+1) + (+7) + (-2)4 = 0Mn (+7)

(+1)2 + (+6)2 + (-2)7 = 0Cr (VI)

(+3)2 + (-2)3 = 0Cr (III)

IUPAC name

Manganese(II)

sulphate

Manganese (IV)

oxide

Manganese(VI)

Manganese(VII)

Chromium(VI)

Chromium(III)

Iron CopperIonic

compoundFeCI2 FeCI3 CuCI CuCI2

OxidationNumber

(+2) + (-1)2 = 0 Fe (+2)

(+3) + (-1)3 = 0 Fe (+3)

(+1) + (-1) = 0 Cu (+1)

(+2) + (-1)2 = 0 Cu (+2)

IUPAC name

Iron (II) chloride Iron (III) chloride Copper (I) chloride Copper (II) chloride

Vanadium

VO2 + VO 2+

(+5) + (-2)2 = +1 V (+5)

(+4) + (-2) = +2 V (+4)

Vanadium (V) Vanadium (IV)

ON for underlined element in ionic compound10

Na2SO3 Na2SO4 NaNO2 NaNO3 (SO3)2- (SO4)2-

(+1)2 + (+4) + (-2)3 = 0 (+1)2 + (+6) + (-2)4 = 0 (+1)+ (+3) + (-2)2 = 0 (+1)+ (+5) + (-2)3 = 0 (+4) + (-2)3 = -2 (+6) + (-2)4 = -2

ON for S = +4 ON for S = +6 ON for N = +3 ON for N = +5 ON for S = +4 ON for S = +6

+1 +4 -2 +1 +6 -2 +1 +3 -2 +1 +5 -2 +4 -2 +6 -2


11 ON for underlined element in compound

OH-1 PO4

3- S2O32- CN-1 OCI-1 H2O2 (HCO3)-1

(-2) + (+1) = -1 (+5) + (-2)4 = -3 (+2)2 + (-2)3 = -2 (+4) + (-5) = -1 (-2) + (+1) = -1 (+1)2 + (-1)2 = 0

ON for O = -2 ON for P = +5 ON for S = +2 ON for C = +4 ON for O = -2 ON for O = -1 ON for C = +4

(+1) + (+4) + (-2)3 = -1

-2 +1 +5 -2 +2 -2 +4 -5 -2 +1 +1 -1 +1 +4 -2

Oxidation Reduction




Rxn involve gain/loss of oxygen/hydrogen

CH4 + 2O2 → CO2 + 2H2O Gain hydrogen

Oxygen reduction

gain oxygen

Carbon oxidation

Rxn involve gain/loss of electron

Oxidation Reduction

Gain ON ↑ Loss ON ↓

Loss electron ↓ Gain electron ↑- broader definition- cover more rxn types

PbO + CO Pb + CO→ 2

Lead Reduction

gain oxygen

Carbon oxidation

(-4) (+4)

(0) (-2)

ON ↑

ON ↓oxygen reduced

carbon oxidized

PbO + CO Pb + CO→ 2

(+2) (0)lead reduced

(+2) (+4)

CH4 + 2O2 → CO2 + 2H2O

ON ↑carbon oxidized

ON ↓loss oxygen


Oxidation – Gain of oxygen ↑

Oxidation – Loss of hydrogen ↓ Reduction – Gain of hydrogen ↑

Reduction – Loss of oxygen ↓

Oxidation Reduction





Loss electron ↓ Gain electron ↑

Ca + O2 CaO→ CH4 + 2O2 CO→ 2+ 2H2Ogain oxygen gain oxygen

Zn + CuO ZnO + Cu→ PbO + CO Pb + CO→ 2loss oxygen loss oxygen

H2S + CI2 S +2HCI →loss hydrogen

H2S + CI2 S + 2HCI →

Redox - Oxidation state change- Electron transfer

CH4 + 2O2 → CO2 + 2H2O

gain hydrogen

Zn + CuSO4 → ZnSO4 + Cu Zn + CI2 → ZnCI2

No gain/loss oxygen/hydrogen

Redox

gain oxygen

gain hydrogen

Reduction

Oxidation

Are these redox rxns?

Most rxn does not involve H2

and O2

carbon oxidized

Oxidation Reduction




Rxn involve gain/loss of oxygen/hydrogen

CH4 + 2O2 → CO2 + 2H2O

Gain hydrogen

oxygen reduced

gain oxygen

carbon oxidized

Rxn involve gain/loss of electron

Oxidation Reduction

Gain ON ↑ Loss ON ↓

Loss electron ↓ Gain electron ↑- broader definition- cover more rxn types

lead reduced

gain oxygen

carbon oxidized

(-4) (+4)

(0) (-2)

ON ↑

ON ↓oxygen reduced

carbon oxidized

(+2) (0)lead reduced

(+2) (+4)

CH4 + 2O2 → CO2 + 2H2O

ON ↑

ON ↓loss oxygen

PbO + CO Pb + CO→ 2PbO + CO Pb + CO→ 2

Oxidizing Agent Reducing Agent

Causes Oxidation Cause Reduction

Undergo reduction Undergo oxidation

Gain electron ↑ Loss electron ↓

Decrease oxidation number ↓

Increase oxidation number ↑

Oxidation Reduction





Loss electron ↓ Gain electron ↑Oxidizing Agent Reducing Agent

MnO4- Fe2+

Cr2O72- SO2

HNO3 I-

H2O2 H2S

CI2 SO3 2-

CI2 + 2KBr- 2KCI→ + Br2

3CuO + 2NH3 3H→ 2O+ 3Cu + N2


(+7) (+2)Mn red - ON ↓

(+2) Fe oxi – ON ↑ (+3)

MnO4- + Fe2+ + 8H+ Mn→ 2+ + Fe3+ 4H2O

Oxidizing agent ↓ Reduction

Reducing agent ↓ Oxidation

Oxidizing Agent

Reducing Agent

MnO4- Fe2+

Reduction Oxidation

Oxidizing Agent

Reducing Agent

CI2 Br-

Reduction Oxidation



(0) CI red – ON ↓ (-1)

(-1) Br - oxi – ON ↑ (0)

Oxidizing Agent

Reducing Agent

CuO NH3

Reduction Oxidation


(-3) NH3 oxi – ON ↑ (0)

Oxidizing agent ↓ Reduction (+2) Cu red – ON ↓ (0)

2HCI + Zn H→ 2 + ZnCI2

(0) Zn oxi – ON ↑ (+2)Reducing agent ↓ Oxidation


(+1) H red – ON ↓ (0)

Oxidizing Agent

Reducing Agent

HCI Zn

Reduction Oxidation


3CuO + 2NH3 3H→ 2O+ 3Cu +N2


(+7) (+2)Mn red - ON ↓

(+2) Fe oxi – ON ↑ (+3)

MnO4- + 8H+ + Fe2+ Mn→ 2+ + Fe3+ 4H2O



Oxidizing Agent Reduction

MnO4- + 5e Mn→ 2+



(0) CI red – ON ↓ (-1)

(-1) Br - oxi – ON ↑ (0)


(-3) NH3 oxi – ON ↑ (0)

Oxidizing agent ↓ Reduction (+2) Cu red – ON ↓ (0)

2HCI + Zn H→ 2 + ZnCI2

(0) Zn oxi – ON ↑ (+2)Reducing agent ↓ Oxidation


(+1) H red – ON ↓ (0)

Reducing Agent Oxidation

Fe 2+ Fe→ 2+ + e- Loss electronIncrease ON ↑

Gain electronDecrease ON ↓


2Br - Br→ 2 + 2e-

Loss electronIncrease ON ↑


CI2 + 2e 2CI→ - Gain electron

Decrease ON ↓


(NH3) -N3- N→ + 3e- Loss electronIncrease ON ↑


(CuO) Cu2+ + 2e Cu→Gain electronDecrease ON ↓


Zn Zn→ 2+ + 2e- Loss electronIncrease ON ↑


2H+ + 2e H→ 2



Half equations

Oxidation rxn

Oxidation half eqn Reduction half eqn

Loss electron ↓

Reduction rxn

Loss hydrogen ↓ Gain oxygen ↑ Gain ON ↑ Gain electron ↑ Gain hydrogen ↑ Loss oxygen ↓ Loss ON ↓

Oxidizing AgentReducing Agent

Oxidation rxn Reduction rxnlose electron

Zn + 2H+ H→ 2 + Zn2+

Zn Zn→ 2+ + 2e 2H+ + 2e H→ 2

(0) ON increase ↑ (+2)

Zn Zn→ 2+ + 2e2H+ + 2e H→ 2 2H+ + Zn Zn→ 2+ + H2

lose electron gain electron

(+1) ON decrease ↓ (0)

Complete full eqn

Zn + Cu2+ Zn→ 2+ + CuOxidation half eqn

Zn Zn→ 2+ + 2elose electron


Reduction half eqn

Cu2+ + 2e Cu→


gain electron

Zn Zn→ 2+ + 2eCu2+ + 2e Cu→Cu2+ + Zn Zn→ 2+ + Cu

Half equations


Half equations


Zn Zn→ 2+ + 2e 2H+ + 2e H→ 2


Zn Zn→ 2+ + 2e2H+ + 2e H→ 2 2H+ + Zn Zn→ 2+ + H2



Complete full eqn

Oxidation half eqn

Zn Zn→ 2+ + 2elose electron


Reduction half eqn

Cu2+ + 2e Cu→


gain electron Zn Zn→ 2+ + 2eCu2+ + 2e Cu→Cu2+ + Zn Zn→ 2+ + Cu

Half equations

Zn + 2HCI H→ 2 + ZnCI2

Zn + 2H+ + 2CI- H→ 2 + Zn2+ + 2CI -

Complete ionic/redox eqn

Zn + 2H+ H→ 2 + Zn2+

spectator ionsspectator ions

Zn + 2H+ H→ 2 + Zn2+

Zn + CuSO4 ZnSO→ 4 + Cu

Zn + Cu2++ SO42- Zn→ 2+ + SO4

2- + Cu

Complete full eqn


spectator ions

Zn + Cu2+ Zn→ 2+ + Cu

Half equations Half equationsZn + Cu2+ Zn→ 2+ + Cu


Half equations


Mg Mg→ 2+ + 2e Pb2+ + 2e Pb→(0) ON increase ↑ (+2)

Mg Mg→ 2+ + 2ePb2+ + 2e Pb →Pb2+ + Mg Mg→ 2+ + Pb



Complete full eqn

Oxidation half eqn

2Br- Br→ 2 + 2e

lose electron

(-1) ON increase ↑ (0)

Reduction half eqn

CI2 + 2e 2CI→ -

(0) ON decrease ↓ (-1)

gain electron 2Br- Br→ 2

+ 2eCI2

+ 2e 2CI→ -

CI2 + 2Br- 2CI→ - + Br2

Half equations

Mg + PbO Pb→ + MgO

Mg + Pb2+ + O2- Pb → + Mg2+ + O 2-


spectator ionsspectator ions

Mg + Pb2+ Pb→ + Mg2+

2KBr + CI2 Br→ 2 + 2KCI

2K+ + 2Br- + CI2 Br→ 2 + 2K+ + 2CI -

Complete full eqn


spectator ions

2Br- + CI2 Br→ 2 + 2CI-

Half equations Half equations

Mg + Pb2+ Pb→ + Mg2+

2Br- + CI2 Br→ 2 + 2CI-

lose electron

MnO4- + 8H+ + 5Fe2+ Mn→ 2+ + 5Fe3+ + 4H2O

Constructing Half and complete redox equation

(+7) (+2)Mn red - ON ↓

(+2) Fe oxi – ON ↑ (+3)

MnO4- + Fe2+ + 8H+ Mn→ 2+ + Fe3+ + 4H2O




MnO4- + 5e Mn→ 2+




Complete full eqnOxidation half eqnReduction half eqn

1. Balance # O -add H2O

2. Balance # H add H+

3. Balance # charges -add electrons

4. Balance # electron transfer

MnO4- Mn→ 2+

MnO4- Mn→ 2+ + 4H2O

MnO4- + 8H+ Mn→ 2++ 4H2O

MnO4- + 8H+ + 5e- Mn→ 2+ + 4H2O

Fe2+ Fe→ 3+

Fe2+ Fe→ 3+ + e-

5Fe2+ 5Fe→ 3+ + 5e-MnO4- + 8H+ + 5e- Mn→ 2+ + 4H2O

x 5x 1

MnO4- + 8H+ + 5e- Mn→ 2+ + 4H2O

5Fe2+ 5Fe→ 3+ + 5e-+

MnO4- - In acidic medium

- Strong oxidizing agentMnO4

- + 8H+ + Fe2+ Mn→ 2+ + Fe3+ 4H2O

2MnO4- + 5SO2+ 2H2O 2Mn→ 2+ + 5SO4

2- + 4H+

Constructing Half and complete redox equation

(+7) (+2)Mn red - ON ↓

(+4) SO2 oxi – ON ↑ (+6)

2MnO4- + 5SO2 + 2H2O 2Mn→ 2+ + 5SO4

2- + 4H+




MnO4- + 5e Mn→ 2+


SO2 SO→ 4

2- + 2e- Loss electronIncrease ON ↑



1. Balance # O - add H2O


3. Balance # charges - add electrons


MnO4- Mn→ 2+

MnO4- Mn→ 2+ + 4H2O

MnO4- + 8H+ Mn→ 2++ 4H2O

MnO4- + 8H+ + 5e- Mn→ 2+ + 4H2O

SO2 SO→ 4

2-

2MnO4- + 16H+ + 10e- 2Mn→ 2+ + 8H2O

x 5x 2

2MnO4- + 16H+ + 10e- 2Mn→ 2+ + 8H2O

5SO2 + 10H2O 5SO→ 42- + 20H+ + 10e-+

2MnO4- + 5SO2 + 2H2O 2Mn→ 2+ + 5SO4

2- 4H+

SO2 + 2H2O SO→ 4

2-

SO2 + 2H2O SO→ 4

2- + 4H+

SO2 + 2H2O SO→ 4

2- + 4H+ + 2e-

5SO2 + 10H2O 5SO→ 4

2- + 20H+ + 10e-

2MnO4- + 5H2O2 + 6H+ 2Mn→ 2+ + 5O2

+ 8H2O

Constructing Half and complete redox equations

(+7) (+2)Mn red - ON ↓

(-1) H2O2 oxi – ON ↑ (0)

2MnO4- + 5H2O2 + 6H+ 2Mn→ 2+ + 5O2

+ 8H2OOxidizing agent ↓ Reduction



MnO4- + 5e Mn→ 2+


H2O2 O→ 2

+ 2e- Loss electronIncrease ON ↑


Complete full eqn Oxidation half eqnReduction half eqn





MnO4- Mn→ 2+

MnO4- Mn→ 2+ + 4H2O

MnO4- + 8H+ Mn→ 2++ 4H2O

MnO4- + 8H+ + 5e- Mn→ 2+ + 4H2O

2MnO4- + 16H+ + 10e- 2Mn→ 2+ + 8H2O

x 5x 2

2MnO4- + 16H+ + 10e- 2Mn→ 2+ + 8H2O

5H2O2 5O→ 2 + 10H+ + 10e-+

2MnO4- + 5H2O2 + 6H+ 2Mn→ 2+ + 5O2

+ 8H2O

H2O2 O→ 2

H2O2 O→ 2 + 2H+

H2O2 O→ 2 + 2H+ + 2e-

5H2O2 5O→ 2 + 10H+ + 10e-

Cr2O72- + 3NO2

- + 8H+ 2Cr→ 3+ + 3NO3- + 4H2O

Cr2O72- 2Cr→ 3+


(+6) (+3)Cr red - ON ↓

(+3) NO2- oxi – ON ↑ (+5)

Cr2O72- + 3NO2

- + 8H+ 2Cr→ 3+ + 3NO3- + 4H2O




Cr2O72- + 6e- 2Cr→ 3+


NO2- NO→ 3

- + 2e- Loss electronIncrease ON ↑






4. Balance # electron transferx 3x 1

Cr2O72- + 14H+ + 6e- 2Cr→ 3+ + 7H2O

3NO2-+ 3H2O 3NO→ 3

- + 6H+ + 6e-+

Cr2O72- + 3NO2

- + 8H+ 2Cr→ 3+ + 3NO3- + 4H2O

Cr2O72- 2Cr→ 3+ + 7H2O

Cr2O72- + 14H+ 2Cr→ 3+ + 7H2O

Cr2O72- + 14H+ + 6e- 2Cr→ 3+ + 7H2O

Cr2O72- + 14H+ + 6e- 2Cr→ 3+ + 7H2O

NO2- NO→ 3

-

NO2- + H2O NO→ 3

-

NO2- + H2O NO→ 3

- + 2H+

NO2- + H2O NO→ 3

- + 2H+ + 2e-

3NO2- + 3H2O 3NO→ 3

- + 6H+ + 6e-

Cr2O72- + 6Fe2+ + 14H+ 2Cr→ 3+ + 6Fe3+ + 7H2O

Cr2O72- 2Cr→ 3+


(+6) (+3)Cr red - ON ↓

(+2) Fe2+ oxi – ON ↑ (+3)

Cr2O72- + 6Fe2+ + 14H+ 2Cr→ 3+ + 6Fe3+ + 7H2O




Cr2O72- + 6e- 2Cr→ 3+


Fe2+ Fe→ 3+ + e- Loss electronIncrease ON ↑







Cr2O72- + 14H+ + 6e- 2Cr→ 3+ + 7H2O

6Fe2+ 6Fe→ 3+ + 6e-+

Cr2O72- 2Cr→ 3+ + 7H2O

Cr2O72- + 14H+ 2Cr→ 3+ + 7H2O

Cr2O72- + 14H+ + 6e- 2Cr→ 3+ + 7H2O

Cr2O72- + 14H+ + 6e- 2Cr→ 3+ + 7H2O

Cr2O72- + 6Fe2+ + 14H+ 2Cr→ 3+ + 6Fe3+ 7H2O

Fe2+ Fe→ 3+

Fe2+ Fe→ 3+ + e

6Fe2+ 6Fe→ 3+ + 6e


(+5) (-1)CIO3 - red - ON ↓

(-1) I- oxi – ON ↑ (0)

CIO3- + 6I- + 6H+ 3I→ 2 + CI- + 3H2O




CIO3- + 6e- CI→ -


2I- I→ 2 + 2e- Loss electron

Increase ON ↑







CIO3- + 6H+ + 6e- CI→ - + 3H2O

6I- 3I→ 2 + 6e-+

CIO3- + 6I- + 6H+ 3I→ 2 + CI- + 3H2O

CIO3- CI→ -

CIO3- CI→ - + 3H2O

CIO3- + 6H+ CI→ - + 3H2O

CIO3- + 6H+ + 6e- CI→ - + 3H2O

CIO3- + 6H+ + 6e- CI→ - + 3H2O

2I- I→ 2

2I- I→ 2 + 2e-

6I- 3I→ 2 + 6e-

CIO3- + 6H++ 6I- 3I→ 2 + 3H2O


(+5) (+2) NO3 - red - ON ↓

(0) Cu oxi – ON ↑ (+2)

2NO3- + 3Cu + 8H+ 3Cu→ 2+ + 2NO + 4H2O




NO3- + 3e- NO→


Cu Cu→ 2+ + 2e- Loss electronIncrease ON ↑







2NO3- + 8H+ + 6e- 2NO→ + 4H2O

3Cu 3Cu→ 2+ + 6e-+

2NO3- + 3Cu + 8H+ 3Cu→ 2+ + 2NO + 4H2O

NO3- NO→

NO3- NO + 2H→ 2O

NO3- + 4H+ NO + 2H→ 2O

NO3- + 4H+ + 3e- NO + 2H→ 2O

2NO3- + 8H+ + 6e- 2NO + 4H→ 2O

Cu Cu→ 2+

Cu Cu→ 2+ + 2e-

3Cu 3Cu→ 2+ + 6e-

2NO3- + 8H+ + 3Cu 3Cu→ 2+ +2NO + 4H2O

HNO3 +3Fe2+ + 3H+ 3Fe→ 3+ + NO + 2H2O


(+5) (+2) HNO3 red - ON ↓

(+2) Fe oxi – ON ↑ (+3)

HNO3 + 3Fe2+ + 3H+ 3Fe→ 3+ + NO + 2H2O




HNO3 + 3e- NO→









HNO3 + 3H+ + 3e- NO→ + 2H2O 3Fe2+ 3Fe→ 3+ + 3e-+

HNO3 NO + 2H→ 2O

HNO3+ 3H+ NO + 2H→ 2O

HNO3 + 3H+ + 3e- NO + 2H→ 2O

HNO3 + 3H+ + 3e- NO + 2H→ 2O

Fe2+ Fe→ 3+

HNO3 + 3Fe2+ + 3H+ 3Fe→ 3+ + NO + 2H2O

HNO3 NO→

Fe2+ Fe→ 3+ + e-

3Fe2+ 3Fe→ 3+ + 3e-

H2O2 + 2Fe2+ +2H+ 2Fe→ 3+ + 2H2O


(-1) (-2) H2O3 red - ON ↓

(+2) Fe oxi – ON ↑ (+3)

H2O2 + 2Fe2+ + 2H+ 2Fe→ 3+ + 2H2O




H2O3 + e- H→ 2O









H2O2 + 2H+ + 2e- 2H→ 2O 2Fe2+ 2Fe→ 3+ + 2e-+

Fe2+ Fe→ 3+

Fe2+ Fe→ 3+ + e-

2Fe2+ 2Fe→ 3+ + 2e-

H2O2 + 2Fe2+ + 2H+ 2Fe→ 3+ + 2H2O

H2O2 H→ 2O

H2O2 2H→ 2O

H2O2 + 2H+ 2H→ 2O

H2O2 + 2H+ + 2e- 2H→ 2O

H2O2 + 2H+ + 2e- 2H→ 2O

CI2 + SO2 + 2H2O 2CI→ - + SO4

2- + 4H+


(0) (-1)CI2 red - ON ↓

(+4) SO2 oxi – ON ↑ (+6)

CI2 + SO2 + 2H2O 2CI→ - + SO4

2- + 4H+




CI2 + 2e 2CI→ -


SO2 SO→ 4

2- + 2e- Loss electronIncrease ON ↑







SO2 SO→ 4

2-

x 1x 1

CI2 + 2e- 2CI→ -

SO2 + 2H2O SO→ 42- + 4H+ + 2e-+

SO2 + 2H2O SO→ 4

2-

SO2 + 2H2O SO→ 4

2- + 4H+

SO2 + 2H2O SO→ 4

2- + 4H+ + 2e-

CI2 + SO2 + 2H2O 2CI→ - + SO4

2- + 4H+

CI2 2CI→ -

CI2 + 2e- 2CI→ -

CI2 + 2e- 2CI→ - SO2

+ 2H2O SO→ 42- + 4H+ + 2e-

MnO4- (Acidic medium)

- Strong oxidizing agent- Gain 5 e-

MnO4- - (Neutral medium)

- Moderate oxidizing agent- Gain 3 e

MnO4- + 2H2O + 3e- MnO→ 2 + 4OH-

MnO4- - (Basic medium)

- Weak oxidizing agent- Gain 1 e

Disproportional Reaction

Substance both oxidized and reduced simultaneouslySubstance acts as oxidizing and reducing agent

Redox Reaction

(-1) Br - oxi – ON ↑ (0)

(0) CI red – ON ↓ (-1)


Reducing agent - oxidizedOxidizing agent – reduced

Oxidizing Agent

Reducing Agent

Concept Map

Redox Reaction in diff medium

(-1) H2O2 red – ON ↓ (-2)

H2O2 H→ 2O + 1/2O2

(-1) H2O2 oxi – ON ↑ (0)

(0) CI2 red – ON ↓ (-1)

CI2 + H2O HOCI→ + HCI

(0) CI2 oxi – ON ↑ (+1)

(+3) HNO2 red – ON ↓ (+2)

HNO2 HNO→ 3 + 2NO + 2H2O

(+3) HNO2 oxi – ON ↑ (+5)

Cu2SO4 CuSO→ 4

+ Cu

(+1) Cu red – ON ↓ (0)

(+1) Cu oxi – ON ↑ (+2)

MnO4- + 8H+ + 5e- Mn→ 2+ + 4H2O

(+7) ON decrease ↓ (+2)


MnO4- + e- MnO→ 4

2-


Sn2+ + 2Fe3+ Sn→ 4+ + 2Fe2+2Fe2+ + CI2 2Fe→ 3+ + 2CI-Ca + 2H+ Ca→ 2+ + H2

IB Redox Questions

Deduce half eqn of oxidation and reduction for the following

Ca + 2H+ Ca→ 2+ + H22Fe2+ + CI2

2Fe→ 3+ + 2CI- Sn2+ + 2Fe3+ Sn→ 4+ + 2Fe2+

0 +1 +2 0

Ca Ca→ 2+ + 2e

2H+ + 2e H→ 2

oxidation

reduction

+2 0 +3 -1

2Fe2+ Fe→ 3+ + 2e

CI2 + 2e 2CI→ -

oxidation

reduction

+2 +3 +4 +2

Sn2+ Sn→ 4+ + 2e

2Fe3+ + 2e 2Fe→ 2+

Substances acting as oxidizing and reducing agent

2MnO4- + 5H2O2 + 6H+ 2Mn→ 2+ + 5O2

+ 8H2O

H2O2 + 2Fe2+ + 2H+ 2Fe→ 3+ + 2H2O

H2O2 + 2I- + 2H+ I→ 2 + 2H2O

Oxidizing Agent Reducing Agent

MnO4- Fe2+

Cr2O72- SO2

HNO3 I-

H2O2 H2S

CI2 SO3 2-

Acidified H2O2 act as oxidizing agent- Oxidizes Fe2+ to Fe3+

- Oxidizes I- to I2

Acidified MnO4- act as more powerful oxidizing agent

-Oxidizes weaker oxidizing agent H2O2 to H2O and O2

- H2O2 act as reducing agent

Identify oxidizing and reducing agent for following rxn.

5As2O3 + 2MnO4

- + 16H+ 2Mn→ 2+ + 5As2O5 + 8H2O 2NO3- + 3Cu + 8H+ 3Cu→ 2+ + 2NO + 4H2O

Cr2O72- + 3NO2

- + 8H+ 2Cr→ 3+ + 3NO3- + 4H2O

1 2

3

oxidizing agent

oxidizing agent

oxidizing agent

reducing agent

reducing agent

reducing agent

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttp://creativecommons.org/licenses/

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttp://lawrencekok.blogspot.com

ib chemistry on redox, oxidizing, reducing agents and writing half redox equations

Education

electron book

element bond

bond covalentredox oxidation

unequal sharingf2 o

diff en values

element formal charge

bond ionic

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