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REDOX REACTIONS REDOX REACTIONS Balancing by the IonBalancing by the Ion--
electron method electron method
(acid medium)(acid medium)
Chemistry
José Manuel Bélmez MacíasRendered by: David Bélmez Macías
KALIUM academiawww.kaliumacademia.com
(+34) 924 104 283 - 655 840 225
REDOX REACTIONS: Balancing by the ionREDOX REACTIONS: Balancing by the ion--electron method (acid medium)electron method (acid medium)Chemistry
José Manuel Bélmez MacíasRendered by: David Bélmez Macías
KALIUM academiawww.kaliumacademia.com
(+34) 924 104 283 - 655 840 225
WhatWhat are are theythey??REDOXREDOX balancingbalancingTheThe ionion--electronelectronmethodmethodCalculatingCalculating oxidationoxidation no.no.IdentifyingIdentifying ofof semisemi--reactionsreactionsIonicIonic halfhalf--reactionsreactionsBalancingBalancing HalfHalf--reactionsreactionsMultiplyingMultiplying halfhalf--reactionsreactionsGlobal Global ionicionic reactionreactionMolecular Molecular reactionreaction
WhatWhat are are theythey?? A redox process is a reaction in which we find an electron transfer.
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
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:
OXIDATION:
REDUCTION:
Where A transfers an electron to B causing its reduction and we would say that A is the REDUCING AGENT
However, if it is B which gets the electron from A, it becomes oxidized, then we would say that B is the OXIDIZING AGENT
INDEX
BalancingBalancing redox redox reactionsreactions The redox reactions adjustment lie in the balance of the chemical equation:
The easiest way is the:
ION–ELECTRON (HALF-REACTION) METHOD
OHKClClMnClHClKMnO 2224 8252162
Before going on werecomend you to download a quick guide of this method in
our Facebook webpage
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDE ESPAÑOLINDEX
1) Calculate the oxidation numbers of each atom in each chemical.
RULES:
OHKClClMnClHClKMnO 2224
The oxidation state of a simple one-atom ion is the same as its charge
The ionThe ion--electron method electron method (acid medium)(acid medium)
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDE ESPAÑOLINDEX
1) Calculate the oxidation numbers of each atom in each chemical.
RULES:
OHKClClMnClHClKMnO 2224 0
The oxidation state of a simple one-atom ion is the same as its chargeThe oxidation state of a free element is zero
The ionThe ion--electron method electron method (acid medium)(acid medium)
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
The ionThe ion--electron method electron method (acid medium)(acid medium)
1) Calculate the oxidation numbers of each atom in each chemical
RULES:
OHKClClMnClHClKMnO 2224 +1 0 +1
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 a simple one-atom ion is the same as its chargeThe oxidation state of a free element is zero
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
RULES:
OHKClClMnClHClKMnO 2224 -2 +1 0 +1 -2
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 ionThe ion--electron method electron method (acid medium)(acid medium)
1) Calculate the oxidation numbers of each atom in each chemical
The oxidation state of a simple one-atom ion is the same as its chargeThe oxidation state of a free element is zeroThe oxidation state of H in its combinations is +1, with the exception of the metal hydrides, where it is -1
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
RULES:
OHKClClMnClHClKMnO 2224 +1 -2 +1 0 +1 +1 -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.)
1) Calculate the oxidation numbers of each atom in each chemical
The ionThe ion--electron method electron method (acid medium)(acid medium)
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 a simple one-atom ion is the same as its chargeThe oxidation state of a free element is zeroThe oxidation state of H in its combinations is +1, with the exception of the metal hydrides, where it is -1
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
RULES:
OHKClClMnClHClKMnO 2224 +1 -2 +1 -1 0 +1 -1 +1 -2
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
1) Calculate the oxidation numbers of each atom in each chemical
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.)
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 a simple one-atom ion is the same as its chargeThe oxidation state of a free element is zeroThe oxidation state of H in its combinations is +1, with the exception of the metal hydrides, where it is -1
The ionThe ion--electron method electron method (acid medium)(acid medium)
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
RULES:
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -2
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
1) Calculate the oxidation numbers of each atom in each chemical
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 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.)
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 a simple one-atom ion is the same as its chargeThe oxidation state of a free element is zeroThe oxidation state of H in its combinations is +1, with the exception of the metal hydrides, where it is -1
The ionThe ion--electron method electron method (acid medium)(acid medium)
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
2) Identify which element is reduced and which is oxidized.
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -2
REDUCTION OXIDATION
The ionThe ion--electron method electron method (acid medium)(acid medium)
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
3) Write down the half-reactions in the ionic mode
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -2
REDUCTION OXIDATION
*¡¡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:
MnO4+7 -2
q=7+4·(-2)=-1 MnO 4-
Reduction:
Oxidation:
MnO 42+-
MnCl - Cl2
The ionThe ion--electron method electron method (acid medium)(acid medium)
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
4) Balance each half-reaction
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -2
REDUCTION
Reduction:
Oxidation:
MnO 42+-
MnCl - Cl2
A) First, elements which are not hydrogen or oxygen are balanced
2
OXIDATION
The ionThe ion--electron method electron method (acid medium)(acid medium)
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
4) Balance each half-reaction
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -2
REDUCTION
MnO 42+-
MnCl - Cl2
B) Oxygen is balanced by adding H2O where necessary
2 OH24
OXIDATION
The ionThe ion--electron method electron method (acid medium)(acid medium)
A) First, elements which are not hydrogen or oxygen are balanced
Reduction:
Oxidation:
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
4) Balance each half-reaction
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -2
REDUCTION
MnO 42+-
MnCl - Cl2
C) Hydrogen is then balanced by adding H+ where necessary
2OH2 4H + 8
OXIDATION
The ionThe ion--electron method electron method (acid medium)(acid medium)
B) Oxygen is balanced by adding H2O where necessary
A) First, elements which are not hydrogen or oxygen are balanced
Reduction:
Oxidation:
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
4) Balance each half-reaction
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -2
REDUCTION
MnO 42+-
MnCl - Cl2
D) Then balance the charges by adding electrons (e-) so that at the end the truth charge is the same in both parts of the reaction
2OH2 4H + 8 5e-
2e-
OXIDATION
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:
MnO 42+-
Mn OH 2 4H + 8 xe-M nO 42+-
Mn OH 2 4H + 8 xe-
x
x=5
The ionThe ion--electron method electron method (acid medium)(acid medium)
C) Hydrogen is then balanced by adding H+ where necessary
B) Oxygen is balanced by adding H2O where necessary
A) First, elements which are not hydrogen or oxygen are balanced
Reduction:
Oxidation:
BASIC MEDIUMGUIDEINDEX
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
ESPAÑOL
5) Multiply each half-reaction with a coefficient for it to have the same number of electrons
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -2
MnO 42+-
MnCl - Cl22
OH2 4H + 8 5e-2e-
( )·2( )·5
The ionThe ion--electron method electron method (acid medium)(acid medium)
REDUCTION OXIDATION
Reduction:
Oxidation:
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
6) Add up boths semi reactions
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -2
MnO 42+-
MnCl - Cl22
OH2 4H + 8 5e-2e-
( )·2( )·5
MnO 42+- Mn OH2 8H +16 Cl -10 Cl222 5
The ionThe ion--electron method electron method (acid medium)(acid medium)
REDUCTION OXIDATION
Reduction:
Oxidation:
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
7) Turn the ionic reaction into molecular
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -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
MnO 42+-
MnCl - Cl22
OH2 4H + 8 5e-2e-
( )·2( )·5
MnO 42+- Mn OH2 8H +16 Cl -10 Cl222 5
The ionThe ion--electron method electron method (acid medium)(acid medium)
REDUCTION OXIDATION
Reduction:
Oxidation:
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
7) Turn the ionic reaction into molecular
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -2
EACH PERMANGANATE ION (MnO4-) CARRIES ONE POTASSIUM ION (K+) IN THE ORIGINAL REACTION
MnO 42+-
MnCl - Cl22
OH2 4H + 8 5e-2e-
( )·2( )·5
MnO 42+- Mn OH2 8H +16 Cl -10 Cl222 5
The ionThe ion--electron method electron method (acid medium)(acid medium)
REDUCTION OXIDATION
Reduction:
Oxidation:
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
7) Turn the ionic reaction into molecular
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -2
EACH PERMANGANATE ION (MnO4-) CARRIES ONE POTASSIUM ION (K+) IN THE ORIGINAL REACTIONAs in each ionic reaction there are two permanganate ions, we add two ions potassium (K+) to each part of the reaction
MnO 42+-
MnCl - Cl22
OH2 4H + 8 5e-2e-
( )·2( )·5
MnO 42+- Mn OH2 8H +16 Cl -10 Cl222 5
K +2 K +2
The ionThe ion--electron method electron method (acid medium)(acid medium)
REDUCTION OXIDATION
Reduction:
Oxidation:
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
7) Turn the ionic reaction into molecular
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -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
MnO 42+-
MnCl - Cl22
OH2 4H + 8 5e-2e-
( )·2( )·5
MnO 42+- Mn OH2 8H +16 Cl -10 Cl2
K + K +
22 52 2
The ionThe ion--electron method electron method (acid medium)(acid medium)
REDUCTION OXIDATION
Reduction:
Oxidation:
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
7) Turn the ionic reaction into molecular
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -2
EACH Mn2+ ION CARRIES TWO CHLORIDE IONS (Cl-) IN THE ORIGINAL REACTION
MnO 42+-
MnCl - Cl22
OH2 4H + 8 5e-2e-
( )·2( )·5
MnO 42+- Mn OH2 8H +16 Cl -10 Cl2
K + K +
22 52 2
The ionThe ion--electron method electron method (acid medium)(acid medium)
REDUCTION OXIDATION
Reduction:
Oxidation:
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
7) Turn the ionic reaction into molecular
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -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
MnO 42+-
MnCl - Cl22
OH2 4H + 8 5e-2e-
( )·2( )·5
MnO 42+- Mn OH2 8H +16 Cl -10 Cl2
K + K +Cl -4 Cl -422 5
2 2
The ionThe ion--electron method electron method (acid medium)(acid medium)
REDUCTION OXIDATION
Reduction:
Oxidation:
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
7) Turn the ionic reaction into molecular
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -2
EACH POTASSIUM ION (K+) CARRIES ONE CHLORIDE ION (Cl-) IN THE ORIGINAL REACTION
MnO 42+-
MnCl - Cl22
OH2 4H + 8 5e-2e-
( )·2( )·5
MnO 42+- Mn OH2 8H +16 Cl -10 Cl2
K + K +Cl -4 Cl -422 5
2 2
The ionThe ion--electron method electron method (acid medium)(acid medium)
REDUCTION OXIDATION
Reduction:
Oxidation:
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
7) Turn the ionic reaction into molecular
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -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
MnO 42+-
MnCl - Cl22
OH2 4H + 8 5e-2e-
( )·2( )·5
MnO 42+- Mn OH2 8H +16 Cl -10 Cl2
K + K +Cl -4 Cl -422 5
2 Cl -22Cl -2
The ionThe ion--electron method electron method (acid medium)(acid medium)
REDUCTION OXIDATION
Reduction:
Oxidation:
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
7) Turn the ionic reaction into molecular
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -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
MnO 42+-
MnCl - Cl22
OH2 4H + 8 5e-2e-
( )·2( )·5
MnO 42+- Mn OH2 8H +16 Cl -10 Cl2
K + K +Cl -4 Cl -4 Cl -Cl -22 5
2 222
The ionThe ion--electron method electron method (acid medium)(acid medium)
REDUCTION OXIDATION
Reduction:
Oxidation:
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
The ionThe ion--electron method electron method (acid medium)(acid medium)
7) Turn the ionic reaction into molecular
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -2
MnO 42+-
MnCl - Cl22
OH2 4H + 8 5e-2e-
( )·2( )·5
MnO 42+- Mn OH2 8H +16 Cl -10 Cl2
K + K +Cl -4 Cl -4 Cl -Cl -22 5
2 222
OHKClClMnClHClKMnO 2224 2 16 2 2
NOW WE GROUP UP THE IONS IN ORDER TO FORM THE SPECIES OF THE ORIGINAL REACTIONS
OHKClClMnClHClKMnO 2224 OHKClClMnClHClKMnO 2224 OHKClClMnClHClKMnO 2224
REDUCTION OXIDATION
Reduction:
Oxidation:
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
7) Turn the ionic reaction into molecular
OHKClClMnClHClKMnO 2224 +1 +7 -2 +1 -1 +2 -1 0 +1 -1 +1 -2
REDUCTION
Reduction:
Oxidation:
MnO 42+-
MnCl - Cl22
OH2 4H + 8 5e-2e-
OXIDATION
( )·2( )·5
MnO 42+- Mn OH2 8H +16 Cl -10 Cl2
K + K +Cl -4 Cl -4 Cl -Cl -22 5
2 222
OHKClClMnClHClKMnO 2224 2 16 2 25 8
IN THE CASE OF THE MOLECULAR SUBSTANCES WE PRESERVE THE COEFFICIENTS
OHKClClMnClHClKMnO 2224 OHKClClMnClHClKMnO 2224 OHKClClMnClHClKMnO 2224
The ionThe ion--electron method electron method (acid medium)(acid medium)
José Manuel Bélmez Macías, Rendered by: David Bélmez Macías
BASIC MEDIUMGUIDEINDEX ESPAÑOL
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