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

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

Yes – 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 CI xx

xx

• x

∂- ∂+

+1 -1 Oxidation 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)





• Unequal sharing electron based on electronegativity

• + means lose electron

• - means gain electron

Oxidation Number/ON Rules

H CI xx

xx

• x

∂- ∂+

+1 -1 Oxidation 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

o

o

xx oo

oo xx

xx o

x

Equal sharing

xx

xx

xx

o

x

+1 -1 Unequal sharing

0 0

xx

xx

xx

o

x

+1 -1

Complete transfer

ox

ox o

o

oo

oo

oo

oo

o

o

xo

xo

Unequal sharing

-2 +4 -2

H O H

CI2 H CI Na CI C O2

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

oo

o

x

o

x

+1 -2 +1

Unequal sharing

H N H

H o

x

o

x

o

x

oo

+1 -3 +1

+1

Unequal sharing

H2 O N H3

H C H

H

H

o

x

o

x o

x

o

x

+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 metal Metal hydride

NaH CaH2

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




• Unequal sharing electron based on electronegativity H CI

xx

∂- xx

• x

Oxidation number +1 -1

∂+

xx

H CI

xx

xx

xx

+1 -1

o

x

Unequal sharing

H CI +1 -1

Na H o

x

+1 -1

Complete transfer

Na H +1 -1

Exceptions


Oxygen -2 O -2

+2

Bond to fluorine

F2O

Exceptions


Oxygen -2 O -2

-1 Peroxide

(O-O)

H2O2

H O H F O F oo

oo

o

x

o

x

+1 -2 +1 Unequal sharing

H2 O +1 -2

oo

oo

xx

xx

xx

xx

xx

xx

o x

o x

-1 +2 -1 Unequal sharing

F2 O -1 +2

O O H H

O-O single bond

oo

oo

oo

oo

o x

o x

o

o

equal sharing

+1 -1 -1 +1 Unequal 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 H

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

F O F O O xx

xx

xx

xx

xx

xx

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

xx xx

o x

o x

-1 +2 -1

F2 O -1 +2

H H oo

oo

oo

oo

o

o

o x

o x

+1 -1 -1 +1

H2 O2 +1 -1

Unequal sharing Unequal sharing





• Unequal sharing electron based on electronegativity H CI

xx

∂- xx

• x

Oxidation number +1 -1

∂+

xx


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

F O F O O xx

xx

xx

xx

xx

xx

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

xx xx

o x

o x

-1 +2 -1

F2 O -1 +2

H H oo

oo

oo

oo

o

o 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 H

H

H

H O N O H O N O N O N

O

O O

O

o x

o x

o x

x x x x

+1 -3 +1

+1

-2

[N H4 ]

-3 +1 +1

Unequal sharing

xx

o x

o x

xo

xo

xx

oo

oo oo

oo

+1 -2 +3 -2

Unequal sharing

H N O2

+1 +3 -2

O

o x

o x

xo

xo

xx

oo

o

o o

o

+1 -2 +5 -2

-2

Unequal sharing

H N O3

+1 +5 -2

o x

o x

xx

oo

xx

oo

o

o

o

o o

o

o

o

o

o o

o

o

o

o

o

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/group ON metal from Gp 1 – 3

ON 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

CI2 0 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 ON Charge on ion

Click here on oxidation rules Click here view simple step

Notes

Sc3+

Charge on Sc

Oxidation

number

+3

Oxidation

state

- + 3+

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch2/oxnumb.html

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch2/oxnumb.html

http://www.wikihow.com/Find-Oxidation-Numbers

http://www.wikihow.com/Find-Oxidation-Numbers

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 CO2 5


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 Mg

0 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)

9 Formula

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

http://www.chemguide.co.uk/inorganic/redox/oxidnstates.html

http://www.chemguide.co.uk/inorganic/redox/oxidnstates.html


9 Metal more than one oxidation states, Roman numeral used

Manganese Chromium

Ionic compound

MnSO4 MnO2 K2MnO4 KMnO4 K2Cr2O7 Cr2O3

Oxidation Number

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

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

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

Mn (+6) (+1) + (+7) + (-2)4 = 0

Mn (+7) (+1)2 + (+6)2 + (-2)7 = 0

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

Cr (III)

IUPAC name

Manganese (II)

sulphate

Manganese (IV)

oxide

Manganese (VI)

Manganese (VII)

Chromium (VI)

Chromium (III)

Iron Copper

Ionic compound

FeCI2 FeCI3 CuCI CuCI2

Oxidation Number

(+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 compound 10

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 reduced

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 + CO2

Lead Reduction

gain oxygen

Carbon oxidized

(-4) (+4)

(0) (-2)

ON ↑

ON ↓ oxygen reduced

carbon oxidized

PbO + CO → Pb + CO2

(+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 → CO2+ 2H2O gain oxygen gain oxygen

Zn + CuO → ZnO + Cu PbO + CO → Pb + CO2

loss 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 + CO2 PbO + CO → Pb + CO2

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→ 3H2O+ 3Cu + N2


(+7) (+2) Mn red - ON ↓

(+2) Fe oxi – ON ↑ (+3)

MnO4- + Fe2+ + 8H+ → Mn2+ + Fe3+ 4H2O

Oxidizing agent

↓

Reduction

Reducing agent

↓

Oxidation Oxidizing

Agent Reducing

Agent

MnO4- Fe2+

Reduction Oxidation

Oxidizing Agent

Reducing Agent

CI2 Br-

Reduction Oxidation

Oxidizing agent

↓

Reduction

Reducing agent

↓

Oxidation

(0) CI red – ON ↓ (-1)

(-1) Br - oxi – ON ↑ (0)

Oxidizing Agent

Reducing Agent

CuO NH3

Reduction Oxidation

Reducing agent

↓

Oxidation

(-3) NH3 oxi – ON ↑ (0)

Oxidizing agent

↓

Reduction (+2) Cu red – ON ↓ (0)

2HCI + Zn → H2 + ZnCI2

(0) Zn oxi – ON ↑ (+2) Reducing agent

↓

Oxidation

Oxidizing agent

↓

Reduction (+1) H red – ON ↓ (0)

Oxidizing Agent

Reducing Agent

HCI Zn

Reduction Oxidation


3CuO + 2NH3→ 3H2O+ 3Cu +N2


(+7) (+2) Mn red - ON ↓

(+2) Fe oxi – ON ↑ (+3)

MnO4- + 8H+ + Fe2+ → Mn2+ + Fe3+ 4H2O

Oxidizing agent

↓

Reduction

Reducing agent

↓

Oxidation

Oxidizing Agent Reduction

MnO4- + 5e → Mn2+

Oxidizing agent

↓

Reduction

Reducing agent

↓

Oxidation

(0) CI red – ON ↓ (-1)

(-1) Br - oxi – ON ↑ (0)

Reducing agent

↓

Oxidation

(-3) NH3 oxi – ON ↑ (0)

Oxidizing agent

↓

Reduction (+2) Cu red – ON ↓ (0)

2HCI + Zn → H2 + ZnCI2

(0) Zn oxi – ON ↑ (+2) Reducing agent

↓

Oxidation

Oxidizing agent

↓

Reduction (+1) H red – ON ↓ (0)

Reducing Agent Oxidation

Fe 2+ → Fe2+ + e- Loss electron

Increase ON ↑

Gain electron

Decrease ON ↓


2Br - → Br2 + 2e-

Loss electron

Increase ON ↑


CI2 + 2e → 2CI- Gain electron

Decrease ON ↓


(NH3) -N3- → N + 3e- Loss electron

Increase ON ↑


(CuO) Cu2+ + 2e → Cu Gain electron

Decrease ON ↓


Zn → Zn2+ + 2e- Loss electron

Increase ON ↑


2H+ + 2e → H2

Gain electron

Decrease ON ↓


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 ↓


Oxidation rxn Reduction rxn lose electron

Zn + 2H+ → H2 + Zn2+

Zn → Zn2+ + 2e 2H+ + 2e → H2

(0) ON increase ↑ (+2)

Zn → Zn2+ + 2e

2H+ + 2e → H2 2H+ + Zn → Zn2+ + H2

lose electron gain electron

(+1) ON decrease ↓ (0)

Complete full eqn

Zn + Cu2+ → Zn2+ + Cu Oxidation half eqn

Zn → Zn2+ + 2e lose electron


Reduction half eqn

Cu2+ + 2e → Cu


gain electron

Zn → Zn2+ + 2e

Cu2+ + 2e → Cu Cu2+ + Zn → Zn2+ + Cu

Half equations


Half equations


Zn → Zn2+ + 2e 2H+ + 2e → H2


Zn → Zn2+ + 2e

2H+ + 2e → H2 2H+ + Zn → Zn2+ + H2



Complete full eqn

Oxidation half eqn

Zn → Zn2+ + 2e lose electron


Reduction half eqn

Cu2+ + 2e → Cu


gain electron

Zn → Zn2+ + 2e

Cu2+ + 2e → Cu Cu2+ + Zn → Zn2+ + Cu

Half equations

Zn + 2HCI → H2 + ZnCI2

Zn + 2H+ + 2CI- → H2 + Zn2+ + 2CI -

Complete ionic/redox eqn

Zn + 2H+ → H2 + Zn2+

spectator ions spectator ions

Zn + 2H+ → H2 + Zn2+

Zn + CuSO4 → ZnSO4 + Cu

Zn + Cu2++ SO42- → Zn2+ + SO4

2- + Cu

Complete full eqn


spectator ions

Zn + Cu2+ → Zn2+ + Cu

Half equations Half equations Zn + Cu2+ → Zn2+ + Cu


Half equations


Mg → Mg2+ + 2e Pb2+ + 2e → Pb


Mg → Mg2+ + 2e

Pb2+ + 2e → Pb Pb2+ + Mg → Mg2+ + Pb



Complete full eqn

Oxidation half eqn

2Br- → Br2 + 2e

lose electron

(-1) ON increase ↑ (0)

Reduction half eqn

CI2 + 2e → 2CI-

(0) ON decrease ↓ (-1)

gain electron

2Br- → Br2 + 2e

CI2 + 2e → 2CI-

CI2 + 2Br- → 2CI- + Br2

Half equations

Mg + PbO → Pb + MgO

Mg + Pb2+ + O2- → Pb + Mg2+ + O 2-


spectator ions spectator ions

Mg + Pb2+ → Pb + Mg2+

2KBr + CI2 → Br2 + 2KCI

2K+ + 2Br- + CI2 → Br2 + 2K+ + 2CI -

Complete full eqn


spectator ions

2Br- + CI2 → Br2 + 2CI-

Half equations Half equations

Mg + Pb2+ → Pb + Mg2+

2Br- + CI2 → Br2 + 2CI-

lose electron

MnO4- + 8H+ + 5Fe2+ → Mn2+ + 5Fe3+ + 4H2O

Constructing Half and complete redox equation

(+7) (+2) Mn red - ON ↓

(+2) Fe oxi – ON ↑ (+3)

MnO4- + Fe2+ + 8H+ → Mn2+ + Fe3+ + 4H2O

Oxidizing agent

↓

Reduction

Reducing agent

↓

Oxidation


MnO4- + 5e → Mn2+



Increase ON ↑

Gain electron

Decrease ON ↓

Complete full eqn Oxidation half eqn Reduction half eqn

1. Balance # O -add H2O

2. Balance # H add H+

3. Balance # charges -add electrons

4. Balance # electron transfer

MnO4- → Mn2+

MnO4- → Mn2+ + 4H2O

MnO4- + 8H+ → Mn2++ 4H2O

MnO4- + 8H+ + 5e- → Mn2+ + 4H2O

Fe2+ → Fe3+

Fe2+ → Fe3+ + e-

5Fe2+ → 5Fe3+ + 5e- MnO4- + 8H+ + 5e- → Mn2+ + 4H2O

x 5 x 1

MnO4- + 8H+ + 5e- → Mn2+ + 4H2O

5Fe2+ → 5Fe3+ + 5e- +

MnO4- - In acidic medium

- Strong oxidizing agent MnO4

- + 8H+ + Fe2+ → Mn2+ + Fe3+ 4H2O

2MnO4- + 5SO2+ 2H2O → 2Mn2+ + 5SO4

2- + 4H+

Constructing Half and complete redox equation

(+7) (+2) Mn red - ON ↓

(+4) SO2 oxi – ON ↑ (+6)

2MnO4- + 5SO2 + 2H2O

→ 2Mn2+ + 5SO42- + 4H+

Oxidizing agent

↓

Reduction

Reducing agent

↓

Oxidation


MnO4- + 5e → Mn2+


SO2 → SO4

2- + 2e- Loss electron

Increase ON ↑

Gain electron

Decrease ON ↓


1. Balance # O - add H2O


3. Balance # charges - add electrons


MnO4- → Mn2+

MnO4- → Mn2+ + 4H2O

MnO4- + 8H+ → Mn2++ 4H2O

MnO4- + 8H+ + 5e- → Mn2+ + 4H2O

SO2 → SO4

2-

2MnO4- + 16H+ + 10e- → 2Mn2+ + 8H2O

x 5 x 2

2MnO4- + 16H+ + 10e- → 2Mn2+ + 8H2O

5SO2 + 10H2O → 5SO42- + 20H+ + 10e-

+

2MnO4- + 5SO2 + 2H2O

→ 2Mn2+ + 5SO42- 4H+

SO2 + 2H2O

→ SO42-

SO2 + 2H2O

→ SO42- + 4H+

SO2 + 2H2O

→ SO42- + 4H+ + 2e-

5SO2 + 10H2O

→ 5SO42- + 20H+ + 10e-

2MnO4- + 5H2O2 + 6H+ → 2Mn2+ + 5O2

+ 8H2O

Constructing Half and complete redox equations

(+7) (+2) Mn red - ON ↓

(-1) H2O2 oxi – ON ↑ (0)

2MnO4- + 5H2O2 + 6H+ → 2Mn2+ + 5O2

+ 8H2O

Oxidizing agent

↓

Reduction

Reducing agent

↓

Oxidation


MnO4- + 5e → Mn2+


H2O2 → O2

+ 2e- Loss electron

Increase ON ↑

Gain electron

Decrease ON ↓






MnO4- → Mn2+

MnO4- → Mn2+ + 4H2O

MnO4- + 8H+ → Mn2++ 4H2O

MnO4- + 8H+ + 5e- → Mn2+ + 4H2O

2MnO4- + 16H+ + 10e- → 2Mn2+ + 8H2O

x 5 x 2

2MnO4- + 16H+ + 10e- → 2Mn2+ + 8H2O

5H2O2 → 5O2 + 10H+ + 10e-

+

2MnO4- + 5H2O2 + 6H+ → 2Mn2+ + 5O2

+ 8H2O

H2O2 → O2

H2O2 → O2 + 2H+

H2O2 → O2 + 2H+ + 2e-

5H2O2 → 5O2 + 10H+ + 10e-

Cr2O72- + 3NO2

- + 8H+ → 2Cr3+ + 3NO3- + 4H2O

Cr2O72-→ 2Cr3+


(+6) (+3) Cr red - ON ↓

(+3) NO2- oxi – ON ↑ (+5)

Cr2O72- + 3NO2

- + 8H+ → 2Cr3+ + 3NO3- + 4H2O

Oxidizing agent

↓

Reduction

Reducing agent

↓

Oxidation


Cr2O72- + 6e- → 2Cr3+


NO2- → NO3

- + 2e- Loss electron

Increase ON ↑

Gain electron

Decrease ON ↓





4. Balance # electron transfer x 3 x 1

Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O

3NO2-+ 3H2O → 3NO3

- + 6H+ + 6e- +

Cr2O72- + 3NO2

- + 8H+ → 2Cr3+ + 3NO3- + 4H2O

Cr2O72- → 2Cr3+ + 7H2O

Cr2O72- + 14H+ → 2Cr3+ + 7H2O

Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O

Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O

NO2- → NO3

-

NO2- + H2O → NO3

-

NO2- + H2O → NO3

- + 2H+

NO2- + H2O → NO3

- + 2H+ + 2e-

3NO2- + 3H2O → 3NO3

- + 6H+ + 6e-

Cr2O72- + 6Fe2+ + 14H+ → 2Cr3+ + 6Fe3+ + 7H2O

Cr2O72-→ 2Cr3+


(+6) (+3) Cr red - ON ↓

(+2) Fe2+ oxi – ON ↑ (+3)

Cr2O72- + 6Fe2+ + 14H+ → 2Cr3+ + 6Fe3+ + 7H2O

Oxidizing agent

↓

Reduction

Reducing agent

↓

Oxidation


Cr2O72- + 6e- → 2Cr3+


Fe2+ → Fe3+ + e- Loss electron

Increase ON ↑

Gain electron

Decrease ON ↓






Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O

6Fe2+ → 6Fe3+ + 6e- +

Cr2O72- → 2Cr3+ + 7H2O

Cr2O72- + 14H+ → 2Cr3+ + 7H2O

Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O

Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O

Cr2O72- + 6Fe2+ + 14H+ → 2Cr3+ + 6Fe3+ 7H2O

Fe2+ → Fe3+

Fe2+ → Fe3+ + e

6Fe2+ → 6Fe3+ + 6e


(+5) (-1) CIO3 - red - ON ↓

(-1) I- oxi – ON ↑ (0)

CIO3- + 6I- + 6H+ → 3I2 + CI- + 3H2O

Oxidizing agent

↓

Reduction

Reducing agent

↓

Oxidation


CIO3- + 6e- → CI-


2I- → I2 + 2e-

Loss electron

Increase ON ↑

Gain electron

Decrease ON ↓






CIO3- + 6H+ + 6e- → CI- + 3H2O

6I- → 3I2 + 6e-

+

CIO3- + 6I- + 6H+ → 3I2 + CI- + 3H2O

CIO3- → CI-

CIO3- → CI- + 3H2O

CIO3- + 6H+ → CI- + 3H2O

CIO3- + 6H+ + 6e- → CI- + 3H2O

CIO3- + 6H+ + 6e- → CI- + 3H2O

2I- → I2

2I- → I2 + 2e-

6I- → 3I2 + 6e-

CIO3- + 6H++ 6I- → 3I2 + 3H2O


(+5) (+2) NO3 - red - ON ↓

(0) Cu oxi – ON ↑ (+2)

2NO3- + 3Cu + 8H+ → 3Cu2+ + 2NO + 4H2O

Oxidizing agent

↓

Reduction

Reducing agent

↓

Oxidation


NO3- + 3e- → NO


Cu → Cu2+ + 2e- Loss electron

Increase ON ↑

Gain electron

Decrease ON ↓






2NO3- + 8H+ + 6e- → 2NO + 4H2O

3Cu → 3Cu2+ + 6e- +

2NO3- + 3Cu + 8H+ → 3Cu2+ + 2NO + 4H2O

NO3- → NO

NO3- → NO + 2H2O

NO3- + 4H+ → NO + 2H2O

NO3- + 4H+ + 3e- → NO + 2H2O

2NO3- + 8H+ + 6e- → 2NO + 4H2O

Cu → Cu2+

Cu → Cu2+ + 2e-

3Cu → 3Cu2+ + 6e-

2NO3- + 8H+ + 3Cu → 3Cu2+ +2NO + 4H2O

HNO3 +3Fe2+ + 3H+ → 3Fe3+ + NO + 2H2O


(+5) (+2) HNO3 red - ON ↓

(+2) Fe oxi – ON ↑ (+3)

HNO3 + 3Fe2+ + 3H+ → 3Fe3+ + NO + 2H2O

Oxidizing agent

↓

Reduction

Reducing agent

↓

Oxidation


HNO3 + 3e- → NO



Increase ON ↑

Gain electron

Decrease ON ↓






HNO3 + 3H+ + 3e- → NO + 2H2O

3Fe2+ → 3Fe3+ + 3e- +

HNO3 → NO + 2H2O

HNO3+ 3H+ → NO + 2H2O

HNO3 + 3H+ + 3e- → NO + 2H2O

HNO3 + 3H+ + 3e- → NO + 2H2O

Fe2+ → Fe3+

HNO3 + 3Fe2+ + 3H+ → 3Fe3+ + NO + 2H2O

HNO3 → NO

Fe2+ → Fe3+ + e-

3Fe2+ → 3Fe3+ + 3e-

H2O2 + 2Fe2+ +2H+ → 2Fe3+ + 2H2O


(-1) (-2) H2O3 red - ON ↓

(+2) Fe oxi – ON ↑ (+3)

H2O2 + 2Fe2+ + 2H+ → 2Fe3+ + 2H2O

Oxidizing agent

↓

Reduction

Reducing agent

↓

Oxidation


H2O3 + e- → H2O



Increase ON ↑

Gain electron

Decrease ON ↓






H2O2 + 2H+ + 2e- → 2H2O

2Fe2+ → 2Fe3+ + 2e- +

Fe2+ → Fe3+

Fe2+ → Fe3+ + e-

2Fe2+ → 2Fe3+ + 2e-

H2O2 + 2Fe2+ + 2H+ → 2Fe3+ + 2H2O

H2O2 → H2O

H2O2 → 2H2O

H2O2 + 2H+ → 2H2O

H2O2 + 2H+ + 2e- → 2H2O

H2O2 + 2H+ + 2e- → 2H2O

CI2 + SO2 + 2H2O → 2CI- + SO4

2- + 4H+


(0) (-1) CI2 red - ON ↓

(+4) SO2 oxi – ON ↑ (+6)

CI2 + SO2 + 2H2O

→ 2CI- + SO42- + 4H+

Oxidizing agent

↓

Reduction

Reducing agent

↓

Oxidation


CI2 + 2e → 2CI-


SO2 → SO4

2- + 2e- Loss electron

Increase ON ↑

Gain electron

Decrease ON ↓






SO2 → SO4

2-

x 1 x 1

CI2 + 2e- → 2CI-

SO2 + 2H2O → SO42- + 4H+ + 2e-

+

SO2 + 2H2O

→ SO42-

SO2 + 2H2O

→ SO42- + 4H+

SO2 + 2H2O

→ SO42- + 4H+ + 2e-

CI2 + SO2 + 2H2O

→ 2CI- + SO42- + 4H+

CI2 → 2CI-

CI2 + 2e- → 2CI-

CI2 + 2e- → 2CI-

SO2 + 2H2O

→ SO42- + 4H+ + 2e-

MnO4- (Acidic medium)

- Strong oxidizing agent

- Gain 5 e-

MnO4- - (Neutral medium)

- Moderate oxidizing agent

- Gain 3 e

MnO4- + 2H2O + 3e- →MnO2 + 4OH-

MnO4- - (Basic medium)

- Weak oxidizing agent

- Gain 1 e

Disproportional Reaction

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

Redox Reaction

(-1) Br - oxi – ON ↑ (0)

(0) CI red – ON ↓ (-1)


Reducing agent - oxidized Oxidizing agent – reduced

Oxidizing

Agent

Reducing

Agent

Concept Map

Redox Reaction in diff medium

(-1) H2O2 red – ON ↓ (-2)

H2O2 → H2O + 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 → HNO3 + 2NO + 2H2O

(+3) HNO2 oxi – ON ↑ (+5)

Cu2SO4 → CuSO4

+ Cu

(+1) Cu red – ON ↓ (0)

(+1) Cu oxi – ON ↑ (+2)

MnO4- + 8H+ + 5e- → Mn2+ + 4H2O

(+7) ON decrease ↓ (+2)


MnO4- + e- → MnO4

2-


Sn2+ + 2Fe3+ → Sn4+ + 2Fe2+ 2Fe2+ + CI2 → 2Fe3+ + 2CI- Ca + 2H+ → Ca2+ + H2

IB Redox Questions

Deduce half eqn of oxidation and reduction for the following

Ca + 2H+ → Ca2+ + H2 2Fe2+ + CI2

→ 2Fe3+ + 2CI- Sn2+ + 2Fe3+ → Sn4+ + 2Fe2+

0 +1 +2 0

Ca → Ca2+ + 2e

2H+ + 2e → H2

oxidation

reduction

+2 0 +3 -1

2Fe2+ → Fe3+ + 2e

CI2 + 2e → 2CI-

oxidation

reduction

+2 +3 +4 +2

Sn2+ → Sn4+ + 2e

2Fe3+ + 2e → 2Fe2+

Substances acting as oxidizing and reducing agent

2MnO4- + 5H2O2 + 6H+ → 2Mn2+ + 5O2

+ 8H2O

H2O2 + 2Fe2+ + 2H+ → 2Fe3+ + 2H2O

H2O2 + 2I- + 2H+ → I2

+ 2H2O


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+ → 2Mn2+ + 5As2O5 + 8H2O 2NO3- + 3Cu + 8H+ → 3Cu2+ + 2NO + 4H2O

Cr2O72- + 3NO2

- + 8H+ → 2Cr3+ + 3NO3- + 4H2O

1 2

3

oxidizing

agent

oxidizing

agent

oxidizing

agent

reducing

agent reducing

agent

reducing

agent

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

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