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1. Chemistry
REDOX REACTIONS
Balancing by the Ionelectron method
(acid medium)
José Manuel Bélmez Macías
Rendered by: David Bélmez Macías
KALIUM academia
www.kaliumacademia.com
(+34) 924 104 283 - 655 840 225

2. Chemistry
REDOX REACTIONS: Balancing by the ion-electron method (acid medium)
What are they?
REDOX balancing
The ion-electron
method
Calculating oxidation no.
Identifying of semi-reactions
Ionic half-reactions
Balancing Half-reactions
Multiplying half-reactions
Global ionic reaction
Molecular reaction
José Manuel Bélmez Macías
Rendered by: David Bélmez Macías
KALIUM academia
www.kaliumacademia.com
(+34) 924 104 283 - 655 840 225

3. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
What are they?
 A redox process is a reaction in which we find an electron transfer.
 In this reactions the element or compound (A) increases its oxidation no. (from n to n+1)
so it is said that it has been oxidized.
 And then another element or compound (B) diminishes its oxidation no. (from m to m-1)
so it is said that it has been reduced.
THIS PROCES THEN COULD BE UNDERSTOOD AS THE ADDITION OF TWO HALF-REACTIONS:
Where A transfers an electron to B causing its
reduction and we would say that A is the
REDUCING AGENT
OXIDATION:
However, if it is B which gets the electron from A, it
becomes oxidized, then we would say that B is the
OXIDIZING AGENT
REDUCTION:
INDEX

4. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
Balancing redox reactions
 The redox reactions adjustment lie in the balance of the chemical equation:
2KMnO4  16HCl  2MnCl2  5Cl2  2KCl  8H 2O
The easiest way is the:
ION–ELECTRON (HALF-REACTION) METHOD
Before going on we
recomend you to download a
quick guide of this method in
our Facebook webpage
INDEX
GUIDE
BASIC MEDIUM
ESPAÑOL

5. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
1) Calculate the oxidation numbers of each atom in each chemical.
KMnO4 
HCl  MnCl2  Cl2  KCl  H 2O
RULES:
The oxidation state of a simple one-atom ion is the same as its charge
INDEX
GUIDE
BASIC MEDIUM
ESPAÑOL

6. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
1) Calculate the oxidation numbers of each atom in each chemical.
KMnO4 
0
HCl  MnCl2  Cl2  KCl  H 2O
RULES:
The oxidation state of a simple one-atom ion is the same as its charge
The oxidation state of a free element is zero
INDEX
GUIDE
BASIC MEDIUM
ESPAÑOL

7. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
1) Calculate the oxidation numbers of each atom in each chemical
KMnO4 
+1
0
+1
HCl  MnCl2  Cl2  KCl  H 2O
RULES:
The oxidation state of a simple one-atom ion is the same as its charge
The oxidation state of a free element is zero
The oxidation state of H in its combinations is +1, with the exception of the metal
hydrides, where it is -1
INDEX
GUIDE
BASIC MEDIUM
ESPAÑOL

8. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
1) Calculate the oxidation numbers of each atom in each chemical
-2
KMnO4 
+1
0
+1
HCl  MnCl2  Cl2  KCl  H 2O
RULES:
The oxidation state of a simple one-atom ion is the same as its charge
The oxidation state of a free element is zero
The oxidation state of H in its combinations is +1, with the exception of the metal
hydrides, where it is -1
The oxidation state of O in its combinations is -2, with the exception of the peroxides,
where it is -1 and in its combination with fluorine, where it will be +2
INDEX
-2
GUIDE
BASIC MEDIUM
ESPAÑOL

9. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
1) Calculate the oxidation numbers of each atom in each chemical
+1
-2
KMnO4 
+1
0
+1
+1
HCl  MnCl2  Cl2  KCl  H 2O
RULES:
The oxidation state of a simple one-atom ion is the same as its charge
The oxidation state of a free element is zero
The oxidation state of H in its combinations is +1, with the exception of the metal
hydrides, where it is -1
The oxidation state of O in its combinations is -2, with the exception of the peroxides,
where it is -1 and in its combination with fluorine, where it will be +2
The oxidation state of the alkaline metals in its combinations is +1 (group 1 of the P.S.)
and +2 for the alkaline earth metals (group 2 of the P.S.)
INDEX
-2
GUIDE
BASIC MEDIUM
ESPAÑOL

10. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
1) Calculate the oxidation numbers of each atom in each chemical
+1
-2
KMnO4 
+1
-1
0
+1 -1
+1
HCl  MnCl2  Cl2  KCl  H 2O
RULES:
The oxidation state of a simple one-atom ion is the same as its charge
The oxidation state of a free element is zero
The oxidation state of H in its combinations is +1, with the exception of the metal
hydrides, where it is -1
The oxidation state of O in its combinations is -2, with the exception of the peroxides,
where it is -1 and in its combination with fluorine, where it will be +2
The oxidation state of the alkaline metals in its combinations is +1 (group 1 of the P.S.)
and +2 for the alkaline earth metals (group 2 of the P.S.)
In the case of the binary salts, the halogen elements behaves with -1, the elements in
the group of O with -2, the elements in the group of N with -3, C and Si -4 and B -3
INDEX
-2
GUIDE
BASIC MEDIUM
ESPAÑOL

11. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
1) Calculate the oxidation numbers of each atom in each chemical
+1 +7
-2
KMnO4 
+1 -1
+2
-1
0
+1 -1
+1
HCl  MnCl2  Cl2  KCl  H 2O
RULES:
The oxidation state of a simple one-atom ion is the same as its charge
The oxidation state of a free element is zero
The oxidation state of H in its combinations is +1, with the exception of the metal
hydrides, where it is -1
The oxidation state of O in its combinations is -2, with the exception of the peroxides,
where it is -1 and in its combination with fluorine, where it will be +2
The oxidation state of the alkaline metals in its combinations is +1 (group 1 of the P.S.)
and +2 for the alkaline earth metals (group 2 of the P.S.)
In the case of the binary salts, the halogen elements behaves with -1, the elements in
the group of O with -2, the elements in the group of N with -3, C and Si -4 and B -3
The algebraic sum of all the oxidation numbers of each atom in a neutral compound is
zero. If the compound is an ion, this addition will be the same as the charge of the ion
INDEX
-2
GUIDE
BASIC MEDIUM
ESPAÑOL

12. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
2) Identify which element is reduced and which is oxidized.
+1 +7
-2
KMnO4 
+1 -1
+2
0
+1 -1
+1
-2
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
INDEX
-1
OXIDATION
GUIDE
BASIC MEDIUM
ESPAÑOL

13. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
3) Write down the half-reactions in the ionic mode
+1 +7
-2
KMnO4 
+1 -1
+2
Oxidation:
0
+1 -1
OXIDATION
-
 Mn
 Cl2
MnO 4
Cl -
2+
*¡¡CAREFUL!!: Only the acids, hydroxides and salts are written the ionic mode
The electric charge (q) comes from the addition of oxidation numbers, then as an
example in the premanganate ion:
+7
-2
MnO4
INDEX
+1
-2
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
q=7+4·(-2)=-1
GUIDE
-
MnO 4
BASIC MEDIUM
ESPAÑOL

14. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
4) Balance each half-reaction
+1 +7
-2
KMnO4 
+1 -1
+2
Oxidation:
0
+1 -1
OXIDATION
-
 Mn
 Cl2
MnO 4
2 Cl -
2+
A) First, elements which are not hydrogen or oxygen are balanced
INDEX
+1
-2
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
GUIDE
BASIC MEDIUM
ESPAÑOL

15. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
4) Balance each half-reaction
+1 +7
-2
KMnO4 
+1 -1
+2
Oxidation:
0
+1 -1
OXIDATION
-
2+
 Mn  4H 2O
 Cl2
MnO 4
2 Cl -
A) First, elements which are not hydrogen or oxygen are balanced
B) Oxygen is balanced by adding H2O where necessary
INDEX
+1
-2
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
GUIDE
BASIC MEDIUM
ESPAÑOL

16. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
4) Balance each half-reaction
+1 +7
-2
KMnO4 
+1 -1
+2
Oxidation:
0
+1 -1
OXIDATION
-
MnO 4  8H
2 Cl -
+
2+
 Mn  4H 2O
 Cl2
A) First, elements which are not hydrogen or oxygen are balanced
B) Oxygen is balanced by adding H2O where necessary
C) Hydrogen is then balanced by adding H+ where necessary
INDEX
+1
-2
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
GUIDE
BASIC MEDIUM
ESPAÑOL

17. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
4) Balance each half-reaction
+1 +7
-2
KMnO4 
+1 -1
+2
Oxidation:
0
+1 -1
+1
-2
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
OXIDATION
-
MnO 4  8H
2 Cl -
2+
5e-
+
Mn  4H 2O
 Cl2 2e-
A) First, elements which are not hydrogen or oxygen are balanced
B) Oxygen is balanced by adding H2O where necessary
C) Hydrogen is then balanced by adding H+ where necessary
D) Then balance the charges by adding electrons (e-) so that at the end the truth charge is the
2+
+
same in both parts of the reaction
THIS STEP IS NORMALLY CONFLICTIVE BUT IT IS NOT
DIFFICULT AT ALL, WE JUST NEED TO BARE IN MIND THAT
THE ELECTRONS ARE PLACED ON THE LEFT IN THE
REDUCTION AND ON THE RIGHT IN THE OXIDATION AND
THAT EACH ONE APORTS A NEGATIVE CHARGE. SO THAT
A SIMPOLE EQUATION CAN BE PLANTED:
INDEX
GUIDE
M nO 4  8 H  xe 

   x 
M n  4 H 2O

x=5
BASIC MEDIUM
ESPAÑOL



18. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
5) Multiply each half-reaction with a coefficient for it to have the same number of electrons
+1 +7
-2
KMnO4 
+1 -1
+2
Oxidation:
+1 -1
+1
OXIDATION
-
( MnO 4  8H
( 2 Cl -
INDEX
0
-2
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
5e-
+
GUIDE
2+
Mn  4H 2O )·2
)·5
 Cl2 2e-
BASIC MEDIUM
ESPAÑOL

19. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
6) Add up boths semi reactions
+1 +7
-2
KMnO4 
+1 -1
+2
Oxidation:
( MnO 4  8H
( 2 Cl -
5e-
+1
-2
+
GUIDE
2+
Mn  4H 2O )·2 
)·5
 Cl2 2e-
+
2 MnO 4 16H  10Cl
INDEX
+1 -1
OXIDATION
-
-
0
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
-
 2Mn  8H 2O  5Cl2
2+
BASIC MEDIUM
ESPAÑOL

20. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
7) Turn the ionic reaction into molecular
+1 +7
-2
+1 -1
KMnO4 
+2
Oxidation:
0
+1 -1
+1
-2
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
OXIDATION
-
( MnO 4  8H
( 2 Cl -
5e-
2 MnO 4 16H  10Cl
-
+
2+
Mn  4H 2O )·2 
)·5
 Cl2 2e-
+
-
 2Mn  8H 2O  5Cl2
2+
THIS STEP IS NORMALLY CONFLICTIVE, HOWEVER IT IS
QUITE EASY IF WE BARE IN MIND THAT THE IONIC
REACTION IS ALREADY ADJUSTED, SO THEN WE ADD THE
IONS WE NEED IN THE SAME CUANTITY AS BOTH PARTS
OF THE REACTION
INDEX
GUIDE
BASIC MEDIUM
ESPAÑOL

21. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
7) Turn the ionic reaction into molecular
+1 +7
-2
KMnO4 
+1 -1
+2
Oxidation:
+1 -1
+1
-2
OXIDATION
-
( MnO 4  8H
( 2 Cl -
5e-
+
2+
Mn  4H 2O )·2 
)·5
 Cl2 2e-
+
2 MnO 4 16H  10Cl
-
0
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
-
 2Mn  8H 2O  5Cl2
2+
EACH PERMANGANATE ION (MnO4-) CARRIES ONE POTASSIUM ION (K+) IN THE ORIGINAL
REACTION
INDEX
GUIDE
BASIC MEDIUM
ESPAÑOL

22. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
7) Turn the ionic reaction into molecular
+1 +7
-2
KMnO4 
+1 -1
+2
Oxidation:
+1 -1
+1
-2
OXIDATION
-
( MnO 4  8H
( 2 Cl -
5e-
+
2+
Mn  4H 2O )·2 
)·5
 Cl2 2e-
+
2 MnO 4 16H  10Cl
+
2K
-
0
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
-
 2Mn  8H 2O  5Cl2
+
2K
2+
EACH PERMANGANATE ION (MnO4-) CARRIES ONE POTASSIUM ION (K+) IN THE ORIGINAL
REACTION
As in each ionic reaction there are two permanganate ions, we add two ions potassium (K+) to
each part of the reaction
INDEX
GUIDE
BASIC MEDIUM
ESPAÑOL

23. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
7) Turn the ionic reaction into molecular
+1 +7
-2
KMnO4 
+1 -1
+2
Oxidation:
+1 -1
+1
-2
OXIDATION
-
( MnO 4  8H
( 2 Cl -
5e-
+
2+
Mn  4H 2O )·2 
)·5
 Cl2 2e-
+
2 MnO 4 16H  10Cl
+
2K
-
0
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
-
 2Mn  8H 2O  5Cl2
+
2K
2+
THE PROTONS (H+) AND THE CHLORIDE IONS (Cl-) MUST MAKE UP THE HYDROCHLORIC ACID,
AND IT IS USEFUL TO LEAVE THE ACIDS TO THE END
INDEX
GUIDE
BASIC MEDIUM
ESPAÑOL

24. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
7) Turn the ionic reaction into molecular
+1 +7
-2
KMnO4 
+1 -1
+2
Oxidation:
+1 -1
( MnO 4  8H
( 2 Cl -
5e-
-2
+
2+
Mn  4H 2O )·2 
)·5
 Cl2 2e-
+
2 MnO 4 16H  10Cl
+
2K
-
 2Mn  8H 2O  5Cl2
+
2K
2+
EACH Mn2+ ION CARRIES TWO CHLORIDE IONS (Cl-) IN THE ORIGINAL REACTION
INDEX
+1
OXIDATION
-
-
0
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
GUIDE
BASIC MEDIUM
ESPAÑOL

25. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
7) Turn the ionic reaction into molecular
+1 +7
-2
KMnO4 
+1 -1
+2
Oxidation:
+1 -1
+1
-2
OXIDATION
-
( MnO 4  8H
( 2 Cl -
5e-
+
2+
Mn  4H 2O )·2 
)·5
 Cl2 2e-
+
2 MnO 4 16H  10Cl
+
2K
4 Cl -
0
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
-
 2Mn  8H 2O  5Cl2
+
4 Cl 2K
2+
EACH Mn2+ ION CARRIES TWO CHLORIDE IONS (Cl-) IN THE ORIGINAL REACTION
As in the ionic reaction there are two Mn2+ ions, we add four chloride ions (Cl-) to each part of the
reaction
INDEX
GUIDE
BASIC MEDIUM
ESPAÑOL

26. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
7) Turn the ionic reaction into molecular
+1 +7
-2
KMnO4 
+1 -1
+2
Oxidation:
+1 -1
+1
-2
OXIDATION
-
( MnO 4  8H
( 2 Cl -
5e-
+
2+
Mn  4H 2O )·2 
)·5
 Cl2 2e-
+
2 MnO 4 16H  10Cl
+
2K
4 Cl -
0
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
-
 2Mn  8H 2O  5Cl2
+
4 Cl 2K
2+
EACH POTASSIUM ION (K+) CARRIES ONE CHLORIDE ION (Cl-) IN THE ORIGINAL REACTION
INDEX
GUIDE
BASIC MEDIUM
ESPAÑOL

27. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
7) Turn the ionic reaction into molecular
+1 +7
-2
KMnO4 
+1 -1
+2
Oxidation:
0
+1 -1
+1
-2
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
OXIDATION
-
( MnO 4  8H
( 2 Cl -
5e-
2+
Mn  4H 2O )·2 
)·5
 Cl2 2e-
+
2 MnO 4 16H  10Cl  2Mn  8H 2O  5Cl2
+
+
2K
4 Cl 2Cl 4 Cl 2K 2Cl -
+
-
2+
EACH POTASSIUM ION (K+) CARRIES ONE CHLORIDE ION (Cl-) IN THE ORIGINAL REACTION
As in the ionic reaction there are two potassium ions (K+), we add two chloride ions (Cl-) to each
part of the reaction
INDEX
GUIDE
BASIC MEDIUM
ESPAÑOL

28. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
7) Turn the ionic reaction into molecular
+1 +7
-2
KMnO4 
+1 -1
+2
Oxidation:
0
+1 -1
+1
-2
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
OXIDATION
-
( MnO 4  8H
( 2 Cl -
5e-
2+
Mn  4H 2O )·2 
)·5
 Cl2 2e-
+
2 MnO 4 16H  10Cl  2Mn  8H 2O  5Cl2
+
+
2K
4 Cl 2Cl 4 Cl 2K 2Cl -
+
-
2+
THE REST OF SPECIES: WATER (H2O) AND CHLORINE (Cl2) BOTH IN THE ORIGINAL AND IN
THE IONIC REACTION ARE THE SAME SO THAT THERE IS NO NEED TO ADD ANYTHING
INDEX
GUIDE
BASIC MEDIUM
ESPAÑOL

29. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
7) Turn the ionic reaction into molecular
+1 +7
-2
KMnO4 
+1 -1
+2
Oxidation:
0
+1 -1
+1
-2
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
OXIDATION
-
( MnO 4  8H
( 2 Cl -
5e-
2+
Mn  4H 2O )·2 
)·5
 Cl2 2e-
+
2 MnO 4 16H  10Cl  2Mn  8H 2O  5Cl2
+
+
2K
4 Cl 2Cl 4 Cl 2K 2Cl -
+
-
2+
NOW WE GROUP UP THE IONS IN ORDER TO FORM THE SPECIES OF THE ORIGINAL
REACTIONS
2KMnO4 16 HCl  2 MnCl2  Cl2  2KCl  H 2O
INDEX
GUIDE
BASIC MEDIUM
ESPAÑOL

30. José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
The ion-electron method (acid medium)
7) Turn the ionic reaction into molecular
+1 +7
-2
KMnO4 
+1 -1
+2
Oxidation:
0
+1 -1
+1
-2
HCl  MnCl2  Cl2  KCl  H 2O
REDUCTION
Reduction:
-1
OXIDATION
-
( MnO 4  8H
( 2 Cl -
5e-
2+
Mn  4H 2O )·2 
)·5
 Cl2 2e-
+
2 MnO 4 16H  10Cl  2Mn  8H 2O  5Cl2
+
+
2K
4 Cl 2Cl 4 Cl 2K 2Cl -
+
-
2+
IN THE CASE OF THE MOLECULAR SUBSTANCES WE PRESERVE THE COEFFICIENTS
2KMnO4 16 HCl  2 MnCl2  5 Cl2  2KCl  8 H 2O
INDEX
GUIDE
BASIC MEDIUM
ESPAÑOL

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