Electrolysis revision notes

Revision notes of electrolysis for IGCSE edexcel chemistry (although i think that it in most courses) :) 

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Electrolysis
Half equations
Oxidation
Is
Loss of electrons
Reduction
Is
Gain of electrons
They show just part of a reaction, from the point of view of one of the
substances present.
They are easily recognisable because they always have an electron (e-) in
them.
Eg. Na Na+ + e- (oxidation ­ a loss of an electron).
Eg. S + 2e- S2- (reduction ­ a gain of two electrons).
If electrons are on the left hand side of the equation ­ reduction.
If electron are on the rights hand side of the equation ­ oxidation.
The charges on both sides have to balance.
Diatomic elements still go round in pairs.
Electrolysis
Involves passing and electric current through an ionic substance that is
either molten or dissolved, and causing a chemical change to take place.
Electrolyte ­ is a substance which undergoes electrolysis. It is an ionic
compound, and doesn't conduct electricity when solid, but does when molten or
dissolved in water because the ions become free to move.
Electricity is passed in and out of the electrolyte via
the two electrodes.
They are often made out of graphite (carbon) or
platinum, because they conduct electricity but are
relatively inert (unreactive), so don't interfere with
any chemical reactions.
Electric current ­ a flow of charged particles.

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Cations are attracted to the cathode
- Anions are attracted to the anode
Electrolysis of lead (II) bromide
When the lead bromide is solid, nothing happens.
When the lead bromide melts:
o The bulb lights up, showing that an electric current is flowing.
o Brown bubbles are seen around the positive electrode (anode) as
bromine gas is released.
o Metallic lead is found underneath the negative electrode (cathode).
Electrolysis of aqueous solutions
A few water molecules split up into H+ + OH- ions.…read more

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Electrolysis of dilute sulphuric acid:
At the cathode : 2H+ + 2e- H2
At the anode: 4OH- 2H2O + O2 + 4e-
For every 4 electrons that flow round the circuit, 1 mole of oxygen is produces
by 2 moles of hydrogen.
Therefore twice the volume of hydrogen.
Electrolysis calculations (:
The Faraday Constant (F) ­
1 mole of electrons provide 96500 coulombs (C) of electricity.
Electricity if the flow of electrons.
Quantity of electricity (C) = no.…read more

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