Electrochemistry Flashcards
What is electrolysis?
The decomposition of a liquid electrolyte using a direct current of electricity
What is an electrolyte?
The liquid or solution that conducts electricity and is decomposed by it
What is a cathode and anode?
Cathode - negative electrode
Anode - positive electrode
What is an electrode?
Do not take part in the electrolysis reactions.
These are graphite rods (unreactive but carry current).
How does electrolysis work?
The electrolyte must be molten or a solution as they can conduct electricity.
Ions in electrolyte are attracted to the oppositely charged electrode.
A reaction occurs at the electrode allowing a product to form and we use half equations to show it.
At cathode - positive metal ions will gain electrons which is reduction.
At cathode - negative non metal ions will lose electrons which is oxidation
Electrolysis of molten lead (ll) bromide
Cathode - product is lead, observation is molten grey liquid, equation - Pb2+ + 2e- - Pb, reduction.
Anode - product is bromine, observation is red/brown pungent fumes, equation - 2Br- - Br + 2e-, oxidation.
Electrolysis of molten lithium chloride
Cathode - product is lithium, observation is molten grey liquid, equation - Li+ + e- - Li, reduction.
Anode - product is chlorine, observation is yellow/green pungent gas, equation - 2Cl- - Cl2 + 2e-, oxidation.
Uses of aluminium
Drink cans.
Take away containers.
Aeroplanes.
Aluminium foil.
Saucepans.
Properties of alumium
Strong, lightweight (low density), good conductor.
Quite reactive but resists corrosion.
Electrolysis to extract aluminium
Bauxite is aluminium ore and is purified to form alumina (aluminium oxide) and dissolved in cryolite.
This is placed in a tank known as a cell and it heated to approximately 900 degrees.
Why is cryolite used in the extraction of aluminium?
For electrolysis to occur the ions must be able to move and the alumina must be molten.
Alumina has a very high melting point which can be reduced by dissolving cryolite, this reduces energy costs.
Cryolite also increases conductivity.
Why can’t aluminium be extracted using carbon?
Aluminium is higher than carbon in reactivity series
Conditions to siting an aluminium extraction plant
Needs large amounts of energy, usually sited near a cheap source of electricity like a hydroelectric station.
Raw materials need to be available and transported easily.
Needs a good water supply for washing, dissolving, cooling and steam generation.
Need facilities to deal with waste disposal.
Advantages of recylcing
More economic - less energy is needed to produce a metal and less damage to the environment.
Fewer quarries and mines, less noise and dust pollution and less heavy traffic.
Saves valuable raw materials - reserves of metal ores will last longer.
Disadvantages of recycling
The collection and transport of used items need organisation, workers, vehicles and fuel.
It can be difficult to sort different materials from one another.
