1013531
Description
Mind Map by Chloe.Sharland, updated more than 1 year ago
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Created by Chloe.Sharland
over 11 years ago
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Redox reactions
- What is a redox reaction?
- Redox reactions involve both reduction and oxidation: reduction is the removal of
oxygen from a substance in a reaction oxidation is the addition of oxygen to a
substance in a reaction, or the reaction of a substance with oxygen
- Redox reactions involve both reduction and oxidation: reduction is the removal of
oxygen from a substance in a reaction oxidation is the addition of oxygen to a
substance in a reaction, or the reaction of a substance with oxygen
- Give an example of a redox reaction?
- The rusting of iron and steel is a redox reaction. It needs oxygen (or air) and water:
iron + oxygen + water → hydrated iron(III) oxide The hydrated iron(III) oxide is the
familiar orange-brown rust we see on rusty iron or steel objects. Oxidation and
reduction can also be explained in terms of electrons: oxidation - loss of electrons
reduction - gain of electrons. Rusting can be explained in terms of electrons. During
the initial stages of rusting: iron loses electrons (it is oxidised) Fe - 2e- → F22+
oxygen gains electrons (it is reduced) 1/2O2 + 2e- + H2O → 2OH-
- The rusting of iron and steel is a redox reaction. It needs oxygen (or air) and water:
iron + oxygen + water → hydrated iron(III) oxide The hydrated iron(III) oxide is the
familiar orange-brown rust we see on rusty iron or steel objects. Oxidation and
reduction can also be explained in terms of electrons: oxidation - loss of electrons
reduction - gain of electrons. Rusting can be explained in terms of electrons. During
the initial stages of rusting: iron loses electrons (it is oxidised) Fe - 2e- → F22+
oxygen gains electrons (it is reduced) 1/2O2 + 2e- + H2O → 2OH-
- How do you prevent rusting?
- There are several ways to prevent iron and steel rusting. Some of
these work because they stop oxygen or water reaching the
surface of the metal: oiling - for example bicycle chains greasing -
for example nut and bolts painting - for example car body panels Iron
and steel objects may also be covered with a layer of metal. Food
cans, for example, are plated with a thin layer of tin.
- Galvanising - is a method of rust prevention. The iron or steel object
is coated in a thin layer of zinc. This stops oxygen and water
reaching the metal underneath - but the zinc also acts as a
sacrificial metal. Zinc is more reactive than iron, so it oxidises in
preference to the iron object.
- Sacrificial protection - The reactivity series lists metals in order of
how reactive they are. Lists from most reactive to least reactive:
potassium, sodium, calcium, magnesium, aluminium, zinc, iron, tin,
lead, copper, silver, gold, platinum. The reactivity series for some
metals Magnesium and zinc are often used as sacrificial metals.
They are more reactive than iron and lose their electrons in
preference to iron. Although tin is used to coat steel cans, it does
not act as a sacrificial metal. Instead, it acts only as a barrier to
stop air and water reaching the surface of the iron or steel. The tin
layer may actually make rusting happen faster if it gets scratched,
because then iron loses electrons in preference to tin.
- There are several ways to prevent iron and steel rusting. Some of
these work because they stop oxygen or water reaching the
surface of the metal: oiling - for example bicycle chains greasing -
for example nut and bolts painting - for example car body panels Iron
and steel objects may also be covered with a layer of metal. Food
cans, for example, are plated with a thin layer of tin.
- Displacement reactions
- Displacement reactions involve a metal and a solution containing a salt of a
different metal. A more reactive metal will displace a less reactive metal from its
compounds. For example, magnesium is more reactive than iron. When a piece
of magnesium is dipped into iron sulfate solution, iron is displaced and coats the
surface of the magnesium: magnesium + iron sulfate → magnesium sulfate +
iron No reaction is seen if iron is dipped into magnesium sulfate solution,
because iron is not reactive enough to displace magnesium.
- Displacement reactions are examples of redox reactions: the ions
of the less reactive metal gain electrons and are reduced the atoms
of the more reactive metal lose electrons and are oxidised For
example, when magnesium displaces iron from iron(II) sulfate
solution: Fe2+ + 2e- → Fe (reduction) Mg - 2e– → Mg2+ (oxidation)
The overall equation is: Mg(s) + FeSO4(aq) → MgSO4(aq) + Fe(s)
Notice that the sulfate ions SO42– are spectator ions (they are
present but do not take part in the reaction).
- Displacement reactions involve a metal and a solution containing a salt of a
different metal. A more reactive metal will displace a less reactive metal from its
compounds. For example, magnesium is more reactive than iron. When a piece
of magnesium is dipped into iron sulfate solution, iron is displaced and coats the
surface of the magnesium: magnesium + iron sulfate → magnesium sulfate +
iron No reaction is seen if iron is dipped into magnesium sulfate solution,
because iron is not reactive enough to displace magnesium.
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