IB Chemistry on Redox, Oxidizing, Reducing Agents and writing half redox equations

1. Redox- Oxidation statechange
- Electron transfer
Zn + CuSO4 → ZnSO4 + Cu Zn + CI2 → ZnCI2No 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 -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)

2. Redox (Oxidationand Reduction)
• 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 Number/ON Rules
H CI
xx
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
Oxidation Number/ON Rules
H CI Na CI
Imagine electron move to more EN element
O C O
oo
o
o
xxoo
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
xo
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

3. 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
• 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 CI
xx
xx
xx
+1 -1
o
x
Unequal sharing
H CI
+1 -1
Na Ho
x
+1 -1
Complete transfer
Na H
+1 -1
Exceptions
Element ON Exception Example
Oxygen -2
O -2
+2
Bond to
fluorine
F2O
Exceptions
Element ON Exception Example
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
ox
ox
-1 +2 -1
Unequal sharing
F2 O
-1 +2
O O HH
O-O single bond
oo
oo
oo
oo
ox
ox
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
ox
ox
+1 -2 +1
Unequal sharing
H2 O
+1 -2
xx
xx
xx xx
xxxx
ox
ox
-1 +2 -1
F2 O
-1 +2
H H
oo
oo
oo
oo
o
o
ox
ox
+1 -1 -1 +1
H2 O2
+1 -1
Unequal sharing Unequal sharing

4. Oxidation Number/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
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
ox
ox
+1 -2 +1
Unequal sharing
H2 O
+1 -2
xx
xx
xx xx
xxxx
ox
ox
-1 +2 -1
F2 O
-1 +2
H H
oo
oo
oo
oo
o
o
ox
ox
+1 -1 -1 +1
H2 O2
+1 -1
Unequal sharing Unequal sharing
Oxidation Number/ON Rules Imagine electron move to more EN element
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
ox
ox
o x
x x
x x
+1 -3 +1
+1
-2
[N H4 ]
-3 +1 +1
Unequal sharing
xx
ox
ox
xo
xo
xx
oo
oo oo
oo
+1 -2 +3 -2
Unequal sharing
H N O2
+1 +3 -2
O
ox
ox
xo
xo
xx
oo
o
o
o
o
+1 -2 +5 -2
-2
Unequal sharing
H N O3
+1 +5 -2
ox
ox
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
+

5. Oxidation Number/ON Rules
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/Nonmetal
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+
K1+ 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 rulesClick here view simple step
Notes
Sc3+
Charge on Sc
Oxidation
number
+3
Oxidation
state
-+
3+

6. 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
Oxidation Number/ON Rules
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
NO3
1-
+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

7. Oxidation Number/ON Rules
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 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

8. Oxidation Number/ON Rules
11 ON for underlined element in compound
OH-1 PO4
3- S2O3
2- 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
Gain oxygen ↑ Loss oxygen ↓
Loss hydrogen ↓ Gain hydrogen ↑
Redox (Oxidationand 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

9. Redox (Oxidation and Reduction)
Oxidation – Gain of oxygen ↑
Oxidation – Loss of hydrogen ↓ Reduction – Gain of hydrogen ↑
Reduction – Loss of oxygen ↓
Oxidation Reduction
Gain oxygen ↑ Loss oxygen ↓
Gain oxidation
Number ↑
Loss oxidation
Number ↓
Loss hydrogen↓ Gain hydrogen ↑
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

10. carbon oxidized
Oxidation Reduction
Gain oxygen ↑ Loss oxygen ↓
Loss hydrogen ↓ Gain hydrogen ↑
Redox (Oxidationand 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 + CO2PbO + 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
Gain oxygen ↑ Loss oxygen ↓
Gain oxidation
Number ↑
Loss oxidation
Number ↓
Loss hydrogen ↓ Gain hydrogen ↑
Loss electron ↓ Gain electron ↑
Oxidizing Agent Reducing Agent
MnO4
- Fe2+
Cr2O7
2- SO2
HNO3 I-
H2O2 H2S
CI2 SO3
2-

11. CI2 + 2KBr-→ 2KCI + Br2
3CuO + 2NH3→ 3H2O+ 3Cu + N2
Redox (Oxidationand Reduction)
(+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

12. CI2 + 2KBr-→ 2KCI + Br2
3CuO + 2NH3→ 3H2O+ 3Cu +N2
Redox (Oxidationand Reduction)
(+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 ↓
Reducing Agent Oxidation
2Br - → Br2 + 2e-
Loss electron
Increase ON ↑
Oxidizing Agent Reduction
CI2 + 2e → 2CI- Gain electron
Decrease ON ↓
Reducing Agent Oxidation
(NH3) -N3- → N + 3e-
Loss electron
Increase ON ↑
Oxidizing Agent Reduction
(CuO) Cu2+ + 2e → Cu
Gain electron
Decrease ON ↓
Reducing Agent Oxidation
Zn → Zn2+ + 2e-
Loss electron
Increase ON ↑
Oxidizing Agent Reduction
2H+ + 2e → H2
Gain electron
Decrease ON ↓

13. Redox (Oxidationand Reduction)
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 ↓
OxidizingAgentReducing Agent
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)
Completefull eqn
Zn + Cu2+ → Zn2+ + CuOxidation half eqn
Zn → Zn2+ + 2e
lose electron
(0) ON increase ↑ (+2)
Reduction half eqn
Cu2+ + 2e → Cu
(+2) ON decrease ↓ (0)
gain electron
Zn → Zn2+ + 2e
Cu2+ + 2e → Cu
Cu2+ + Zn → Zn2+ + Cu
Half equations

14. Redox (Oxidationand Reduction)
Half equations
Oxidation half eqn Reduction half eqn
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)
Completefull eqn
Oxidation half eqn
Zn → Zn2+ + 2e
lose electron
(0) ON increase ↑ (+2)
Reduction half eqn
Cu2+ + 2e → Cu
(+2) ON decrease ↓ (0)
gain electron
Zn → Zn2+ + 2e
Cu2+ + 2e → Cu
Cu2+ + Zn → Zn2+ + Cu
Half equations
Zn + 2HCI → H2 + ZnCI2
Zn + 2H+ + 2CI- → H2 + Zn2+ + 2CI -
Completeionic/redox eqn
Zn + 2H+ → H2 + Zn2+
spectator ionsspectator ions
Zn + 2H+ → H2 + Zn2+
Zn + CuSO4 → ZnSO4 + Cu
Zn + Cu2++ SO4
2- → Zn2+ + SO4
2- + Cu
Completefull eqn
Completeionic/redox eqn
spectator ions
Zn + Cu2+ → Zn2+ + Cu
Half equations Half equations
Zn + Cu2+ → Zn2+ + Cu

15. Redox (Oxidationand Reduction)
Half equations
Oxidation half eqn Reduction half eqn
Mg → Mg2+ + 2e Pb2+ + 2e → Pb
(0) ON increase ↑ (+2)
Mg → Mg2+ + 2e
Pb2+ + 2e → Pb
Pb2+ + Mg → Mg2+ + Pb
lose electron gain electron
(+2) ON decrease ↓ (0)
Completefull 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-
Completeionic/redox eqn
spectator ionsspectator ions
Mg + Pb2+ → Pb + Mg2+
2KBr + CI2 → Br2 + 2KCI
2K+ + 2Br- + CI2 → Br2 + 2K+ + 2CI -
Completefull eqn
Completeionic/redox eqn
spectator ions
2Br- + CI2 → Br2 + 2CI-
Half equations Half equations
Mg + Pb2+ → Pb + Mg2+
2Br- + CI2 → Br2 + 2CI-
lose electron

16. MnO4
- + 8H+ + 5Fe2+ → Mn2+ + 5Fe3+ + 4H2O
ConstructingHalf 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
Oxidizing Agent Reduction
MnO4
- + 5e → Mn2+
Reducing Agent Oxidation
Fe 2+ → Fe2+ + e-
Loss electron
Increase ON ↑
Gain electron
Decrease ON ↓
Completefull eqn
Oxidation half eqnReduction 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 5x 1
MnO4
- + 8H+ + 5e- → Mn2+ + 4H2O
5Fe2+ → 5Fe3+ + 5e-
+
MnO4
- - In acidic medium
- Strong oxidizing agent
MnO4
- + 8H+ + Fe2+ → Mn2+ + Fe3+ 4H2O

17. 2MnO4
- + 5SO2+ 2H2O → 2Mn2+ + 5SO4
2- + 4H+
ConstructingHalf and complete redox equation
(+7) (+2)Mn red - ON ↓
(+4) SO2 oxi – ON ↑ (+6)
2MnO4
- + 5SO2 + 2H2O→ 2Mn2+ + 5SO4
2- + 4H+
Oxidizing agent
↓
Reduction
Reducing agent
↓
Oxidation
Oxidizing Agent Reduction
MnO4
- + 5e → Mn2+
Reducing Agent Oxidation
SO2 → SO4
2- + 2e-
Loss electron
Increase ON ↑
Gain electron
Decrease ON ↓
Completefull eqn
Oxidation half eqnReduction 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
SO2 → SO4
2-
2MnO4
- + 16H+ + 10e- → 2Mn2+ + 8H2O
x 5x 2
2MnO4
- + 16H+ + 10e- → 2Mn2+ + 8H2O
5SO2 + 10H2O → 5SO4
2- + 20H+ + 10e-
+
2MnO4
- + 5SO2 + 2H2O→ 2Mn2+ + 5SO4
2- 4H+
SO2 + 2H2O → SO4
2-
SO2 + 2H2O → SO4
2- + 4H+
SO2 + 2H2O → SO4
2- + 4H+ + 2e-
5SO2 + 10H2O → 5SO4
2- + 20H+ + 10e-

18. 2MnO4
- + 5H2O2 + 6H+ → 2Mn2+ + 5O2 + 8H2O
ConstructingHalf 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
Oxidizing Agent Reduction
MnO4
- + 5e → Mn2+
Reducing Agent Oxidation
H2O2 → O2 + 2e-
Loss electron
Increase ON ↑
Gain electron
Decrease ON ↓
Completefull eqn
Oxidation half eqnReduction 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
2MnO4
- + 16H+ + 10e- → 2Mn2+ + 8H2O
x 5x 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-

19. Cr2O7
2- + 3NO2
- + 8H+ → 2Cr3+ + 3NO3
- + 4H2O
Cr2O7
2-→ 2Cr3+
ConstructingHalf and complete redox equations
(+6) (+3)Cr red - ON ↓
(+3) NO2
- oxi – ON ↑ (+5)
Cr2O7
2- + 3NO2
- + 8H+ → 2Cr3+ + 3NO3
- + 4H2O
Oxidizing agent
↓
Reduction
Reducing agent
↓
Oxidation
Oxidizing Agent Reduction
Cr2O7
2- + 6e- → 2Cr3+
Reducing Agent Oxidation
NO2
- → NO3
- + 2e-
Loss electron
Increase ON ↑
Gain electron
Decrease ON ↓
Completefull eqn
Oxidation half eqnReduction half eqn
1. Balance # O - add H2O
2. Balance# H add H+
3. Balance# charges - add electrons
4. Balance# electron transfer
x 3x 1
Cr2O7
2- + 14H+ + 6e- → 2Cr3+ + 7H2O
3NO2
-+ 3H2O → 3NO3
- + 6H+ + 6e-
+
Cr2O7
2- + 3NO2
- + 8H+ → 2Cr3+ + 3NO3
- + 4H2O
Cr2O7
2- → 2Cr3+ + 7H2O
Cr2O7
2- + 14H+ → 2Cr3+ + 7H2O
Cr2O7
2- + 14H+ + 6e- → 2Cr3+ + 7H2O
Cr2O7
2- + 14H+ + 6e- → 2Cr3+ + 7H2O
NO2
- → NO3
-
NO2
- + H2O → NO3
-
NO2
- + H2O → NO3
- + 2H+
NO2
- + H2O → NO3
- + 2H+ + 2e-
3NO2
- + 3H2O → 3NO3
- + 6H+ + 6e-

20. Cr2O7
2- + 6Fe2+ + 14H+ → 2Cr3+ + 6Fe3+ + 7H2O
Cr2O7
2-→ 2Cr3+
ConstructingHalf and complete redox equations
(+6) (+3)Cr red - ON ↓
(+2) Fe2+ oxi – ON ↑ (+3)
Cr2O7
2- + 6Fe2+ + 14H+ → 2Cr3+ + 6Fe3+ + 7H2O
Oxidizing agent
↓
Reduction
Reducing agent
↓
Oxidation
Oxidizing Agent Reduction
Cr2O7
2- + 6e- → 2Cr3+
Reducing Agent Oxidation
Fe2+ → Fe3+ + e-
Loss electron
Increase ON ↑
Gain electron
Decrease ON ↓
Completefull eqn
Oxidation half eqnReduction half eqn
1. Balance # O - add H2O
2. Balance# H add H+
3. Balance# charges - add electrons
4. Balance# electron transfer
x 6x 1
Cr2O7
2- + 14H+ + 6e- → 2Cr3+ + 7H2O
6Fe2+ → 6Fe3+ + 6e-
+
Cr2O7
2- → 2Cr3+ + 7H2O
Cr2O7
2- + 14H+ → 2Cr3+ + 7H2O
Cr2O7
2- + 14H+ + 6e- → 2Cr3+ + 7H2O
Cr2O7
2- + 14H+ + 6e- → 2Cr3+ + 7H2O
Cr2O7
2- + 6Fe2+ + 14H+ → 2Cr3+ + 6Fe3+ 7H2O
Fe2+ → Fe3+
Fe2+ → Fe3+ + e
6Fe2+ → 6Fe3+ + 6e

21. ConstructingHalf and complete redox equations
(+5) (-1)CIO3
- red - ON ↓
(-1) I- oxi – ON ↑ (0)
CIO3
- + 6I- + 6H+ → 3I2 + CI- + 3H2O
Oxidizing agent
↓
Reduction
Reducing agent
↓
Oxidation
Oxidizing Agent Reduction
CIO3
- + 6e- → CI-
Reducing Agent Oxidation
2I- → I2 + 2e-
Loss electron
Increase ON ↑
Gain electron
Decrease ON ↓
Completefull eqn
Oxidation half eqnReduction half eqn
1. Balance # O - add H2O
2. Balance# H add H+
3. Balance# charges - add electrons
4. Balance# electron transfer
x 3x 1
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

22. ConstructingHalf and complete redox equations
(+5) (+2)NO3
- red - ON ↓
(0) Cu oxi – ON ↑ (+2)
2NO3
- + 3Cu + 8H+ → 3Cu2+ + 2NO + 4H2O
Oxidizing agent
↓
Reduction
Reducing agent
↓
Oxidation
Oxidizing Agent Reduction
NO3
- + 3e- → NO
Reducing Agent Oxidation
Cu → Cu2+ + 2e-
Loss electron
Increase ON ↑
Gain electron
Decrease ON ↓
Completefull eqn
Oxidation half eqnReduction half eqn
1. Balance # O - add H2O
2. Balance# H add H+
3. Balance# charges - add electrons
4. Balance# electron transfer
x 3x 2
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

23. HNO3 +3Fe2+ + 3H+ → 3Fe3+ + NO + 2H2O
ConstructingHalf and complete redox equations
(+5) (+2)HNO3 red - ON ↓
(+2) Fe oxi – ON ↑ (+3)
HNO3 + 3Fe2+ + 3H+ → 3Fe3+ + NO + 2H2O
Oxidizing agent
↓
Reduction
Reducing agent
↓
Oxidation
Oxidizing Agent Reduction
HNO3 + 3e- → NO
Reducing Agent Oxidation
Fe 2+ → Fe3++ e-
Loss electron
Increase ON ↑
Gain electron
Decrease ON ↓
Completefull eqn
Oxidation half eqnReduction half eqn
1. Balance # O - add H2O
2. Balance# H add H+
3. Balance# charges - add electrons
4. Balance# electron transfer
x 3x 1
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-

24. H2O2 + 2Fe2+ +2H+ → 2Fe3+ + 2H2O
ConstructingHalf and complete redox equations
(-1) (-2)H2O3 red - ON ↓
(+2) Fe oxi – ON ↑ (+3)
H2O2 + 2Fe2+ + 2H+ → 2Fe3+ + 2H2O
Oxidizing agent
↓
Reduction
Reducing agent
↓
Oxidation
Oxidizing Agent Reduction
H2O3 + e- → H2O
Reducing Agent Oxidation
Fe 2+ → Fe3++ e-
Loss electron
Increase ON ↑
Gain electron
Decrease ON ↓
Completefull eqn
Oxidation half eqnReduction half eqn
1. Balance # O - add H2O
2. Balance# H add H+
3. Balance# charges - add electrons
4. Balance# electron transfer
x 2x 1
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

25. CI2 + SO2 + 2H2O → 2CI- + SO4
2- + 4H+
ConstructingHalf and complete redox equations
(0) (-1)CI2 red - ON ↓
(+4) SO2 oxi – ON ↑ (+6)
CI2 + SO2 + 2H2O→ 2CI- + SO4
2- + 4H+
Oxidizing agent
↓
Reduction
Reducing agent
↓
Oxidation
Oxidizing Agent Reduction
CI2 + 2e → 2CI-
Reducing Agent Oxidation
SO2 → SO4
2- + 2e-
Loss electron
Increase ON ↑
Gain electron
Decrease ON ↓
Completefull eqn
Oxidation half eqnReduction half eqn
1. Balance # O - add H2O
2. Balance# H add H+
3. Balance# charges - add electrons
4. Balance# electron transfer
SO2 → SO4
2-
x 1x 1
CI2 + 2e- → 2CI-
SO2 + 2H2O → SO4
2- + 4H+ + 2e-
+
SO2 + 2H2O → SO4
2-
SO2 + 2H2O → SO4
2- + 4H+
SO2 + 2H2O → SO4
2- + 4H+ + 2e-
CI2 + SO2 + 2H2O→ 2CI- + SO4
2- + 4H+
CI2 → 2CI-
CI2 + 2e- → 2CI-
CI2 + 2e- → 2CI-
SO2 + 2H2O → SO4
2- + 4H+ + 2e-

26. 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
DisproportionalReaction
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)
CI2 + 2KBr-→ 2KCI + Br2
Reducing agent - oxidized
Oxidizingagent – 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)
(+7) ON decrease ↓ (+4)
MnO4
- + e- → MnO4
2-
(+7) ON decrease ↓ (+6)

27. 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+
Substancesacting as oxidizingand reducing agent
2MnO4
- + 5H2O2 + 6H+ → 2Mn2+ + 5O2 + 8H2O
H2O2 + 2Fe2+ + 2H+ → 2Fe3+ + 2H2O
H2O2 + 2I- + 2H+ → I2 + 2H2O
Oxidizing Agent Reducing Agent
MnO4
- Fe2+
Cr2O7
2- 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 oxidizingand reducing agentfor following rxn.
5As2O3 + 2MnO4
- + 16H+ → 2Mn2+ + 5As2O5 + 8H2O 2NO3
- + 3Cu + 8H+ → 3Cu2+ + 2NO+ 4H2O
Cr2O7
2- + 3NO2
- + 8H+ → 2Cr3+ + 3NO3
- + 4H2O
1 2
3
oxidizing
agent
oxidizing
agent
oxidizing
agent
reducing
agent
reducing
agent
reducing
agent