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3.2.4 Redox
Energetics - Kinetics - Equilibria - Redox - Group VII - Group II - Metal Extraction - Haloalkanes - Alkenes - Alcohols - Analytical Tech... - Unit 1
Oxidation States
The oxidation state tells you the number of electrons an atom has donated (oxidised) or gained (reduced).
Oxidation states follow 6 rules
1. In an element; the oxidation state is always zero.
e.g. Cl2, Cl2 is an element therefore oxidation state is zero.
Oxidation states follow 6 rules
1. In an element; the oxidation state is always zero.
e.g. Cl2, Cl2 is an element therefore oxidation state is zero.
Practice Questions
EASY
Give the oxidation states of these ions
- Na+
- F-
- Ca2+
- OH-
- CO3 2-
- NO3 2-
- HCl
- SO2
- CO3 2-
- ClO4 -
- Cu2O
- HSO4 -
- CO
- CO2
- CCl4
- C
- CaCO3
- C3H6
- P4
- PH3
- PO4 2-
- P2F4
- PBr5
- P2H4
- Cu
- S
- H
Practice Questions
EASY
Give the oxidation states of these ions
Na+
F-
Ca2+
Give the overall oxidation states of the following ions.
OH-
CO3 2-
NO3 2-
Medium
Work out the oxidation states of all the elements in the following compounds and compound ions.
HCl
SO2
CO3 2-
ClO4 -
Cu2O
HSO4 -
Work out the oxidation states of carbon in the following;
CO
CO2
CCl4
C
CaCO3
C3H6
Work out the oxidation states of phosphorous in the following;
P4
PH3
PO4 2-
P2F4
PBr5
P2H4
Hard
Look at this reaction;
Cu + H2SO4 → CuSO4 + H2
Give the oxidation states of the following elements at the beginning and the end of the reaction.
Cu
S
H
EASY
Give the oxidation states of these ions
Na+
F-
Ca2+
Give the overall oxidation states of the following ions.
OH-
CO3 2-
NO3 2-
Medium
Work out the oxidation states of all the elements in the following compounds and compound ions.
HCl
SO2
CO3 2-
ClO4 -
Cu2O
HSO4 -
Work out the oxidation states of carbon in the following;
CO
CO2
CCl4
C
CaCO3
C3H6
Work out the oxidation states of phosphorous in the following;
P4
PH3
PO4 2-
P2F4
PBr5
P2H4
Hard
Look at this reaction;
Cu + H2SO4 → CuSO4 + H2
Give the oxidation states of the following elements at the beginning and the end of the reaction.
Cu
S
H
Half Equations
We can express each part of a redox reaction with half equations. You can be asked to combine half equations to produce full equations (may need balancing).
Half the equations show 1 species and electrons
..... if the species is reduced the electrons are on the LHS
..... if the species is oxidised the electron are on the RHS
Half the equations show 1 species and electrons
..... if the species is reduced the electrons are on the LHS
..... if the species is oxidised the electron are on the RHS
Example 1:
When magnesium burns in oxygen to form magnesium oxide. MgO
Oxygen is reduced to form…..O2-
O2 + 4e- —-> 2O2-
Magnesium is oxidised to form Mg2+
Mg --—> Mg2+ + 2e-
Putting both equations together we will need to balance them to have the same number of e- on both sides to cancel them out.
O2 + 2Mg —> 2MgO
When magnesium burns in oxygen to form magnesium oxide. MgO
Oxygen is reduced to form…..O2-
O2 + 4e- —-> 2O2-
Magnesium is oxidised to form Mg2+
Mg --—> Mg2+ + 2e-
Putting both equations together we will need to balance them to have the same number of e- on both sides to cancel them out.
O2 + 2Mg —> 2MgO
Example 2:
When aluminium reacts with chlorine to form aluminium chloride.
Chlorine is reduced to form…..Cl-
Cl2 + 2e- —-> 2Cl-
Aluminium is oxidised to form Al3+
Al --—> Al3+ + 3e-
Putting both equations together we will need to balance them to have the same number of e- on both sides to cancel them out.
1.5Cl2 + Al —> AlCl3
First we balanced the oxidation states in AlCl to get AlCl3, then we balanced the equation.
When aluminium reacts with chlorine to form aluminium chloride.
Chlorine is reduced to form…..Cl-
Cl2 + 2e- —-> 2Cl-
Aluminium is oxidised to form Al3+
Al --—> Al3+ + 3e-
Putting both equations together we will need to balance them to have the same number of e- on both sides to cancel them out.
1.5Cl2 + Al —> AlCl3
First we balanced the oxidation states in AlCl to get AlCl3, then we balanced the equation.
Now try;
- Lithium reacting with oxygen
- sodium reacting with chlorine
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Energetics - Kinetics - Equilibria - Redox - Group VII - Group II - Metal Extraction - Haloalkanes - Alkenes - Alcohols - Analytical Tech... - Unit 1