Redox Reactions – Revision Pack (C6)
Redox and Rusting:
‘Redox reaction’ references two processes that work together:
-
Reduction (Is Gain)
Oxidation (Is Loss)
Rusting is a redox reaction:
Iron + Oxygen + Water  Hydrated Iron (III) Oxide
Galvanizing iron protects it from rusting by covering it with a
protective layer of zinc. This zinc layer stops oxygen and water
from reaching the surface of the iron.
Zinc also acts a sacrificial metal, this is because it oxidises in
preference to iron (it loses or sacrifices electrons) – this is because
zinc is more reactive than iron.
Redox Extension:
Redox reactions can be thought of in terms of electrons:
A substance is said to have been oxidised if it loses electrons. An oxidising agent
takes electrons away from another object.
A substance is said to have been reduced if it gains electrons. A reducing agent
transfers electrons to another object.
An example of an oxidising agent is oxygen in rusting. The oxygen takes electrons
away from the iron – the oxygen gains these electrons, so in the rusting reaction:
-
Iron loses electrons – so is oxidised
Oxygen gains electrons – so is reduced
Redox reactions can be thought of as reversible reactions; they can be forced in
either direction. In the redox reactions, one direction is oxidation and the other
reduction. For example:
1) The oxidation of iron = (Fe  Fe2+ + e-)
But this can be reversed to the reduction of Fe2+ = (Fe2+ + e-  Fe).
2) The oxidation of Fe2+ = (Fe2+  Fe3+ + e-)
But this can be reversed to the reduction of Fe3+ = (Fe3+ + e-  Fe2+)
3) The reduction of Cl 2 = (Cl 2 + 2e-  2Cl-)
But this can be reversed to the oxidation of 2Cl- = (2Cl-  Cl 2 + 2e-)
Redox Reactions – Revision Pack (C6)
Displacement Reactions:
When you write the word equation for a displacement reaction, the
more reactive metal swaps place with the less reactive one; for
example, sodium is more reactive than zinc, so zinc is displaced:
Sodium + Zinc Sulphate  Sodium Sulphate + Zinc
The order of reactivity (to the left) is needed to work out which metals
will displace other metals.
You will NEED to know the order of magnesium, zinc, iron and tin.
Magnesium is the most reactive, so will displace the other three.
Zinc is the second most reactive, so will displace iron and tin.
Iron is third most reactive, so will only displace tin.
Tin is the least reactive out of the four, so will not displace any.
Displacement – Explained:
Displacement reactions will happen between a reactive metal and compounds of a
less reactive metal. The general formula is:
Reactive
Metal
Element
+
Less
Reactive
Metal
Compound
Reactive
Metal
Compound
+
Less
Reactive
Metal
Element
All metals react by pushing electrons out and turning into ions – this is oxidation.
These electrons are forced onto the ions of other atoms that are not as reactive.
The metal atoms that gain the electrons are reduced; for example:
The SO4 cancels out!
The Mg is oxidised.
Mg + ZnSO 4  MgSO 4 + Zn
Mg + Zn2+  Mg2+ + Zn
The Zn is reduced because the
electrons from the Mg are
forced onto the Zn2+.
If you coat iron in tin, rusting will happen at a faster rate because the tin is less
reactive. A layer of zinc or magnesium is often used because it is more reactive and
will lose electrons in preference to the iron.
Redox Reactions – Revision Pack (C6)
Past Papers:
PPQ(1):
Redox Reactions – Revision Pack (C6)
PPQ(2):
Redox Reactions – Revision Pack (C6)
PPQ(3):
Redox Reactions – Revision Pack (C6)
PPQ(4):
Redox Reactions – Revision Pack (C6)
Mark Schemes:
PPQ(1):
PPQ(2):
PPQ(3):
PPQ(4):