ib chemistry on redox, oxidizing, reducing agents and writing half redox equations
TRANSCRIPT
http://lawrencekok.blogspot.com
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)
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
Oxidation Number/ON Rules
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
Element ON Exception Example
Oxygen -2 O -2
+2Bond to fluorine
F2O
Exceptions
Element ON Exception Example
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
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 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 Number/ON Rules Imagine electron move to more EN element
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+
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/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
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
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
Oxidation Number/ON Rules
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
Oxidation Number/ON Rules
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
Gain oxygen ↑ Loss oxygen ↓
Loss hydrogen ↓ Gain hydrogen ↑
Redox (Oxidation and 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
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 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
Gain oxygen ↑ Loss oxygen ↓
Loss hydrogen ↓ Gain hydrogen ↑
Redox (Oxidation and 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
Gain oxygen ↑ Loss oxygen ↓
Gain oxidation Number ↑
Loss oxidation Number ↓
Loss hydrogen ↓ Gain hydrogen ↑
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
Redox (Oxidation and Reduction)
(+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
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 H→ 2 + 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
CI2 + 2KBr- 2KCI→ + Br2
3CuO + 2NH3 3H→ 2O+ 3Cu +N2
Redox (Oxidation and Reduction)
(+7) (+2)Mn red - ON ↓
(+2) Fe oxi – ON ↑ (+3)
MnO4- + 8H+ + Fe2+ Mn→ 2+ + Fe3+ 4H2O
Oxidizing agent ↓ Reduction
Reducing agent ↓ Oxidation
Oxidizing Agent Reduction
MnO4- + 5e Mn→ 2+
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 H→ 2 + ZnCI2
(0) Zn oxi – ON ↑ (+2)Reducing agent ↓ Oxidation
Oxidizing agent ↓ Reduction
(+1) H red – ON ↓ (0)
Reducing Agent Oxidation
Fe 2+ Fe→ 2+ + e- Loss electronIncrease ON ↑
Gain electronDecrease ON ↓
Reducing Agent Oxidation
2Br - Br→ 2 + 2e-
Loss electronIncrease ON ↑
Oxidizing Agent Reduction
CI2 + 2e 2CI→ - Gain electron
Decrease ON ↓
Reducing Agent Oxidation
(NH3) -N3- N→ + 3e- Loss electronIncrease ON ↑
Oxidizing Agent Reduction
(CuO) Cu2+ + 2e Cu→Gain electronDecrease ON ↓
Reducing Agent Oxidation
Zn Zn→ 2+ + 2e- Loss electronIncrease ON ↑
Oxidizing Agent Reduction
2H+ + 2e H→ 2
Gain electronDecrease ON ↓
Redox (Oxidation and 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 ↓
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
(0) ON increase ↑ (+2)
Reduction half eqn
Cu2+ + 2e Cu→
(+2) ON decrease ↓ (0)
gain electron
Zn Zn→ 2+ + 2eCu2+ + 2e Cu→Cu2+ + Zn Zn→ 2+ + Cu
Half equations
Redox (Oxidation and Reduction)
Half equations
Oxidation half eqn Reduction half eqn
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
Oxidation half eqn
Zn Zn→ 2+ + 2elose electron
(0) ON increase ↑ (+2)
Reduction half eqn
Cu2+ + 2e Cu→
(+2) ON decrease ↓ (0)
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
Complete ionic/redox eqn
spectator ions
Zn + Cu2+ Zn→ 2+ + Cu
Half equations Half equationsZn + Cu2+ Zn→ 2+ + Cu
Redox (Oxidation and Reduction)
Half equations
Oxidation half eqn Reduction half eqn
Mg Mg→ 2+ + 2e Pb2+ + 2e Pb→(0) ON increase ↑ (+2)
Mg Mg→ 2+ + 2ePb2+ + 2e Pb →Pb2+ + Mg Mg→ 2+ + Pb
lose electron gain electron
(+2) ON decrease ↓ (0)
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-
Complete ionic/redox eqn
spectator ionsspectator ions
Mg + Pb2+ Pb→ + Mg2+
2KBr + CI2 Br→ 2 + 2KCI
2K+ + 2Br- + CI2 Br→ 2 + 2K+ + 2CI -
Complete full eqn
Complete ionic/redox 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
Oxidizing agent ↓ Reduction
Reducing agent ↓ Oxidation
Oxidizing Agent Reduction
MnO4- + 5e Mn→ 2+
Reducing Agent Oxidation
Fe 2+ Fe→ 2+ + e- Loss electronIncrease ON ↑
Gain electronDecrease ON ↓
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+
Oxidizing agent ↓ Reduction
Reducing agent ↓ Oxidation
Oxidizing Agent Reduction
MnO4- + 5e Mn→ 2+
Reducing Agent Oxidation
SO2 SO→ 4
2- + 2e- Loss electronIncrease ON ↑
Gain electronDecrease ON ↓
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
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
Reducing agent ↓ Oxidation
Oxidizing Agent Reduction
MnO4- + 5e Mn→ 2+
Reducing Agent Oxidation
H2O2 O→ 2
+ 2e- Loss electronIncrease ON ↑
Gain electronDecrease ON ↓
Complete full 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- 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+
Constructing Half and complete redox equations
(+6) (+3)Cr red - ON ↓
(+3) NO2- oxi – ON ↑ (+5)
Cr2O72- + 3NO2
- + 8H+ 2Cr→ 3+ + 3NO3- + 4H2O
Oxidizing agent ↓ Reduction
Reducing agent ↓ Oxidation
Oxidizing Agent Reduction
Cr2O72- + 6e- 2Cr→ 3+
Reducing Agent Oxidation
NO2- NO→ 3
- + 2e- Loss electronIncrease ON ↑
Gain electronDecrease ON ↓
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 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+
Constructing Half and complete redox equations
(+6) (+3)Cr red - ON ↓
(+2) Fe2+ oxi – ON ↑ (+3)
Cr2O72- + 6Fe2+ + 14H+ 2Cr→ 3+ + 6Fe3+ + 7H2O
Oxidizing agent ↓ Reduction
Reducing agent ↓ Oxidation
Oxidizing Agent Reduction
Cr2O72- + 6e- 2Cr→ 3+
Reducing Agent Oxidation
Fe2+ Fe→ 3+ + e- Loss electronIncrease ON ↑
Gain electronDecrease ON ↓
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 transferx 6x 1
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
Constructing Half and complete redox equations
(+5) (-1)CIO3 - red - ON ↓
(-1) I- oxi – ON ↑ (0)
CIO3- + 6I- + 6H+ 3I→ 2 + CI- + 3H2O
Oxidizing agent ↓ Reduction
Reducing agent ↓ Oxidation
Oxidizing Agent Reduction
CIO3- + 6e- CI→ -
Reducing Agent Oxidation
2I- I→ 2 + 2e- Loss electron
Increase ON ↑
Gain electronDecrease ON ↓
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 transferx 3x 1
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
Constructing Half and complete redox equations
(+5) (+2) NO3 - red - ON ↓
(0) Cu oxi – ON ↑ (+2)
2NO3- + 3Cu + 8H+ 3Cu→ 2+ + 2NO + 4H2O
Oxidizing agent ↓ Reduction
Reducing agent ↓ Oxidation
Oxidizing Agent Reduction
NO3- + 3e- NO→
Reducing Agent Oxidation
Cu Cu→ 2+ + 2e- Loss electronIncrease ON ↑
Gain electronDecrease ON ↓
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 transferx 3x 2
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
Constructing Half and complete redox equations
(+5) (+2) HNO3 red - ON ↓
(+2) Fe oxi – ON ↑ (+3)
HNO3 + 3Fe2+ + 3H+ 3Fe→ 3+ + NO + 2H2O
Oxidizing agent ↓ Reduction
Reducing agent ↓ Oxidation
Oxidizing Agent Reduction
HNO3 + 3e- NO→
Reducing Agent Oxidation
Fe 2+ Fe→ 3+ + e- Loss electronIncrease ON ↑
Gain electronDecrease ON ↓
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 transferx 3x 1
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
Constructing Half and complete redox equations
(-1) (-2) H2O3 red - ON ↓
(+2) Fe oxi – ON ↑ (+3)
H2O2 + 2Fe2+ + 2H+ 2Fe→ 3+ + 2H2O
Oxidizing agent ↓ Reduction
Reducing agent ↓ Oxidation
Oxidizing Agent Reduction
H2O3 + e- H→ 2O
Reducing Agent Oxidation
Fe 2+ Fe→ 3+ + e- Loss electronIncrease ON ↑
Gain electronDecrease ON ↓
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 transferx 2x 1
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+
Constructing Half 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 SO→ 4
2- + 2e- Loss electronIncrease ON ↑
Gain electronDecrease ON ↓
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
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)
CI2 + 2KBr- 2KCI→ + Br2
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)
(+7) ON decrease ↓ (+4)
MnO4- + e- MnO→ 4
2-
(+7) ON decrease ↓ (+6)
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
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Prepared by Lawrence Kok
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