Electrolysis

Electrolysis notes for (i)GCSE chemistry.  Hope you find them useful :)

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  • Created on: 27-04-13 14:25
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Electrolysis
Ionic compounds conduct electricity when molten or aqueous.
When an electric current is passed through a molten ionic compound or an
aqueous solution of an ionic compound, electrolysis takes place.
Electrolysis is the decomposition of a substance by passing an electric
current through it.
Electrolysis of molten compounds
The substance being electrolysed is the electrolyte.
The electrical connections in the circuit are called electrodes.
The positive is the anode, the negative is the cathode.
The products of electrolysing a molten binary compound can be shown by the
following rules:
Metal is formed at the cathode.
Non-metal is formed at the anode.
E.g. PbBr2 Pb ­ cathode Br2 ­ anode
NaCl Na ­ cathode Cl2 ­ anode
How it works:
At Cathode: Positive metal ions are attracted to the negative electrode. At the
electrode they gain electrons so become atoms (rather than ions).
E.g. Pb2+ + 2e- Pb Lead formed

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At Anode: Negative non-metal ions are attracted to the anode. At the anode they
lose electrons of form atoms.
E.g. 2Br- Br2 + 2e- Bromine formed.
Electrolysis of aqueous solutions
Any aqueous solution containing ions can be electrolysed.
The products are harder to predict than with molten compounds.
Product at cathode is either hydrogen or a metal.
Product at anode is usually oxygen but sometimes another non-metal.
If the salt metal is above hydrogen in the reactivity series then hydrogen is
formed at the cathode.…read more

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Overall reaction: 2 NaCl (aq) + 2 H2O (l) 2 NaOH (aq) + H2 (g) + Cl2 (g)
NaCl (aq) is gradually converted into NaOH (aq)…read more

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