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Slide 1

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By Claire Hagger…read more

Slide 2

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Redox Reactions
· A loss of electrons is called oxidation and a gain of
electrons is called reduction. REDuction and
OXidation happen at the same time hence REDOX.
An oxidising agent accepts electrons and gets
reduced and a reducing agent donates electrons
and get oxidised.
· Displacement reactions are redox reactions. It's
always the metal ion that gains electrons and so is
reduced. The metal atoms looses electrons and so
is oxidised.…read more

Slide 3

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Rusting of Iron
· Rusting happens when iron comes into contact with both oxygen from the air and
water. It is a form of hydrated iron (III) oxide.
· Iron+water+oxygenhydrated iron (III) oxide
· It is a redox reaction because each iron atom loses three electrons to become Fe3+.
Iron is oxidised. Oxygen gains two electrons when it reacts with iron to become O2-.
Oxygen's reduced.
· Metals can be combined with other metals to make alloys- this prevents rust, e.g.
stainless steel.
· By coating the iron is a barrier it can prevent rusting as it keeps water and oxygen
out. Painting is best for larger structures and it makes they look nicer. Oiling or
greasing is used when moving parts are involved- e.g. bike chains.
· Tin plating is where a coat of tin is applied to object e.g. food cans. The tin acts as a
barrier stopping water and air reaching the iron. However, this only works if the tin
remains in tact, if it is scratched then the iron will lose electrons in preference to the
tin and it will rust even faster.
· There is also a sacrificial method where a more reactive metal is put with the iron so
that the water and air react with this and not the iron. Galvansing is when zinc is
coated on the object. It is more reactive so loses electrons instead of the iron. Blocks
of metal can also be bolted to the iron such as magnesium. IT IS NOT A
DISPLACEMENT REACTION!!! There is not a metal reacting with a metal salt.…read more

Slide 4

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Electrolysis 1
· Electrolysis is the breaking down of a substance using electricity.
· An electric current is passed through a molten or dissolved ionic compound causing it
to decompose.
· This creates a flow of charge through the electrolyte.
· The positive ions in the solution move towards the cathode (negative) and gain
· The negative ions in the solution move towards the anode (positive) and lose
· As ions gain or lose electrons they become atoms or molecules and are discharged
from the solution at the electrodes.
· In aqueous solutions, as well as the ions from the solute, there are hydrogen ions
(H+) and hydroxide ions (OH-) from the water.
· Sometimes it's easier to discharge the ions from the water than the ones in the
· This means hydrogen could be produced at the cathode and oxygen at the anode.
· The electrolysis of NaOH and HSO are both redox reactions, reduction takes place
at the cathode and oxidation takes place at the anode.…read more

Slide 5

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Electrolysis 3
· The amount of product made during electrolysis depends
on the number of electrons that are transferred. If you
increase the number of electrons, you increase the amount
of substance you produce. This is done by electrolysing for
a longer time or increasing the current.
· Current is the flow of charge and it's charge that
determines how much product is formed during
electrolysis. More charge means more product. The
amount of charge (Q, measured in coulombs) flowing
through a circuit is equal to the current (I) multiplied by the
time in seconds (t): Q=IT
· This means that the charge and the amount of product
created during electrolysis are directly proportional to the
time taken and current used.…read more

Slide 6

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Fuel Cells 1
· Hydrogen and oxygen react to produce water, the reaction is exothermic
(releases energy).
· A fuel cell is an electrical cell that's supplied with a fuel and oxygen and uses
energy from the reaction between them to produce electrical energy
efficiently. There are many different types but the main one is hydrogen-
oxygen fuel cell. This cell combines hydrogen and oxygen to produce heat
energy and clean water so there are no nasty pollutants.
· Hydrogen-oxygen fuel cells involve a redox reaction:
­ The electrolyte is a solution of potassium hydroxide. The electrodes are porous
carbon with a catalyst.
­ Hydrogen goes into the anode compartment and oxygen in the cathode
­ At the cathode (negative), oxygen gains electrons and reacts with water to make OH-
ions. This is reduction.
­ OH- ions in the electrolyte move to the anode.
­ At the anode (positive), hydrogen combines with the hydroxide to make water and
electrons. The hydrogen loses electrons so is oxidised.
­ The electrons flow through an external circuit from the anode to the cathode- this is
the electric current.
­ The overall reaction is hydrogen and oxygen make water.…read more

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