Topic 3 – Redox I
In order to develop their practical skills, students should be encouraged to carry out a range of practical experiments related to this topic. Possible
experiments include simple test tube reactions to investigate redox systems. Mathematical skills that could be developed in this topic include using
an algebraic method to work out the oxidation number of an element within a complex species, balancing equations for redox reactions by
combining ionic half-equations. Within this topic, students can consider how the concept of oxidation number provides a more considered route for
the process of balancing chemical equations.
1. know what is meant by the term ‘oxidation number’
Define the term ‘oxidation number’.
The oxidation number is an indication of the degree of oxidation (loss of electrons) of an atom in a chemical
compound. It is the hypothetical charge that an atom would have, assuming 100% ionic bonds.
2. be able to calculate the oxidation number of elements in compounds and ions.
The use of oxidation numbers in peroxides (O = -1) and metal hydrides (H = -1) is expected.
What is the oxidation number of S in H2SO4? // State the oxidation number of S in S4O62-.
We know that H = +1, and O = -2, so 2 - 8 + S = 0. Therefore S = +6.
// O = -2, so 4S – 12 = -2, therefore S = +5/2.
3. understand oxidation and reduction in terms of electron transfer and changes in oxidation number,
applied to reactions of s- and p-block elements
Prove the reaction 2NH3 + NaClO -> N2H4 + NaCl + H2O is a redox reaction.
NH3 NaClO N2H4 NaCl H2O Change?
Here, NH3 loses
electrons, so is N -3 -2 +1 change
oxidised and so
is the reducing H +1 +1 +1 no change
agent. NaClO
gains electrons, Na +1 +1 no change
so is reduced
and so is the Cl +1 -1 -2 change
oxidising agent.
Not confusing O -2 -2 no change
at all…
4. understand oxidation and reduction in terms of electron loss or electron gain
How can oxidation and reduction be remembered?
OIL RIG – Oxidation Is Loss, Reduction Is Gain (of electrons).
5/6. know that oxidising agents gain electrons, and that that reducing agents lose electrons
Explain that, pal!
Oxidising agents are themselves reduced, so gain electrons in the process. Reducing agents are themselves oxidised,
so lose electrons in the process.
7. understand what a disproportionation reaction involves
What is the USP of a disproportionation reaction?
In order to develop their practical skills, students should be encouraged to carry out a range of practical experiments related to this topic. Possible
experiments include simple test tube reactions to investigate redox systems. Mathematical skills that could be developed in this topic include using
an algebraic method to work out the oxidation number of an element within a complex species, balancing equations for redox reactions by
combining ionic half-equations. Within this topic, students can consider how the concept of oxidation number provides a more considered route for
the process of balancing chemical equations.
1. know what is meant by the term ‘oxidation number’
Define the term ‘oxidation number’.
The oxidation number is an indication of the degree of oxidation (loss of electrons) of an atom in a chemical
compound. It is the hypothetical charge that an atom would have, assuming 100% ionic bonds.
2. be able to calculate the oxidation number of elements in compounds and ions.
The use of oxidation numbers in peroxides (O = -1) and metal hydrides (H = -1) is expected.
What is the oxidation number of S in H2SO4? // State the oxidation number of S in S4O62-.
We know that H = +1, and O = -2, so 2 - 8 + S = 0. Therefore S = +6.
// O = -2, so 4S – 12 = -2, therefore S = +5/2.
3. understand oxidation and reduction in terms of electron transfer and changes in oxidation number,
applied to reactions of s- and p-block elements
Prove the reaction 2NH3 + NaClO -> N2H4 + NaCl + H2O is a redox reaction.
NH3 NaClO N2H4 NaCl H2O Change?
Here, NH3 loses
electrons, so is N -3 -2 +1 change
oxidised and so
is the reducing H +1 +1 +1 no change
agent. NaClO
gains electrons, Na +1 +1 no change
so is reduced
and so is the Cl +1 -1 -2 change
oxidising agent.
Not confusing O -2 -2 no change
at all…
4. understand oxidation and reduction in terms of electron loss or electron gain
How can oxidation and reduction be remembered?
OIL RIG – Oxidation Is Loss, Reduction Is Gain (of electrons).
5/6. know that oxidising agents gain electrons, and that that reducing agents lose electrons
Explain that, pal!
Oxidising agents are themselves reduced, so gain electrons in the process. Reducing agents are themselves oxidised,
so lose electrons in the process.
7. understand what a disproportionation reaction involves
What is the USP of a disproportionation reaction?
