Electrolysis
This is the process where ionic substances are broken down using electricity into smaller simpler substances.
Ionic substances are compounds formed when a metal reacts with a non metal.
They contain charged particles called ions.
Ions are free to move when dissolved in water so it allows electrolysis to happen.
Ions are free when the substances are molten or dissolved in water.
Cations ( positively charged ions ) move to the cathode ( negatively charged electrode) They lose electrons so they are oxidised
Anions (negatively charged ions ) move to the anode (positively charged electrode) They gain electrons so they are reduced
OILRIG
Oxidation is loss of electrons
Reduction is gain of electrons
Electrodes are conductors which are in contact with a circuit to a battery.
Electrolyte is a substance which in solution will conduct electricity.
Electroplating
This is the process where we cover metals with another metal often more expensive.
The cathode is electroplated
the anode is the metal that is used to coat the cathode.
the electrolyte should be a solution of the same metal of the anode.
E.g
Silver can be used to coat cheap jewellry,
Silver is the anode and a cheaper metal like copper is placed at the cathode
The electrolyte is silver nitrate.
This can also be used to purify copper of both the anode and cathode are copper and the solution is copper sulphate
Aluminium extraction
Aluminium is the most abundant metal on earth, however it can only be extracted using electrolysis.
Bauxite is an aluminium ore. An ore is a rock that contains enough concentration of the metal you want to be economically viable to extract.
Bauxite is purified to get aluminium oxide.
Electrolysis is done.
The aluminium oxide is dissolved in molten cryolite, this is used to reduce the melting point so it would be cheaper than melting aluminium oxide as the melting point is over 2000 degrees.
Graphite is used as a cathode and the anode.
Aluminium is formed at the cathode and sinks to the bottom of the tank where it can be tapped off.
Oxygen is formed at the positive electrode, this reacts with the carbon to produce carbon dioxide.
As a result, the anode has to be replaced frequently but carbon is cheap.
Hydrogen and metals form positive ions (cations).
If we use electrolysis on metals more reactive than hydrogen in a solution of water, hydrogen will bubble out as the metal would displace the hydrogen ions in water and form the metal oxide.
We can only use electrolysis on solution with metals less reactive than water like copper as they would be the ones that move to the cathode.
The negative ion in solution will move to the anode, normally these are nonmetals.
Since most nonmetals are gases at room temperature, they will bubble off at the anode.
Chloride ions will form chlorine Cl2 when they are oxidised.
This also follow the rules previously
the more reactive element will be the one that leaves, oxygen will leave if the solution has sulfur ions.
Chlorine
We can make chlorine and hydrogen by electrolysis of dissolved sodium chloride (salt)
Since hydrogen is more reactive then sodium, the H+ ions leave at the cathode
Since chloride ions are more reactive than oxygen ions, Cl- leave at the anode.
The sodium ions and oxygen ions are left behind and form a sodium hydroxide solution NaOH which is an alkaline.
Hydrogen can be used as fuel and for making ammonia.
Chlorine can be used to kill bacterial and to make bleach + plastics
Sodium hydroxide can be used to make soap and bleach.
Half equations.
Reactants are ions and electrons
Products are molecules.
Electrons are shown as e- we add or take away electrons.
2Cl- - 2e- = Cl2
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