Electrochemistry Flashcards
(17 cards)
What is electrolysis
Decomposition of a liquid electrolyte using a direct current of electricity
What is an electrolyte
Liquid or solution that conducts electricity and is decomposed by it.
Will be an ionic compound either molten or dissolved in water
What are electrodes
Metal strips or graphite rods placed in liquid and are connected to a source of electricity .
They are inert which means don’t take part in reactions
What is the negative electrode
The Cathode
What does the cathode do
Attracts positive ions or cations
When ions reach the cathode they gain electrons to become neutral atoms
What is the positive electrode
anode
What does the anode do
Attracts negative ions or anions
When the ions reach the anode they lose electrons to become neutral atoms
What is Molten Electrolytes
When ionic solids become molten they consist of positive and negative ions. These ions can move. The positive ion will move
towards the cathode and lose electrons, while the negative ion
will move towards the anode and gain electrons.
Whats an example of molten electrolytes
Lead ions (Pb 2+ ) are attracted to the cathode. Here they gain
electrons. The half equation at the cathode is:
Pb 2+ (l) + 2e - Pb (l)
What is the main ore of aluminium
Bauxite
What does bauxite contain
Hydrated aluminium oxide
how is electrolysis used to extract aluminium
Ore is crushed, dried and purified. Then the aluminium oxide is dissolved in molten cryolite. This lowers melting point of aluminium oxide
Lead ions (Pb 2+ ) are attracted to the cathode. Here they gain
electrons. The half equation at the cathode is:
Pb 2+ (l) + 2e - Pb (l)
What happens at the cathode in the extraction of aluminium
Molten aluminium is deposited at the cathode. It sinks to the bottomof the tank, where it is tapped off.
Al 3+ + 3e - Al
What happens at the anode in the extraction of aluminium
Oxygen is given off at the anodes.
2O 2- O 2 + 4e -
Because the electrolysis is carried out at high temperatures, the
oxygen reacts with the carbon anodes.
C + O 2 CO 2
This means that the anodes have to be continually replaced.
Why is extraction of aluminium very expensive
Large amount of electricity needed to extract aluminiumH
How can costs be reduced in the extraction of aluminium
Cryolite makes process more cost effective by lowering melting point of aluminium oxide and increasing conductivity of electrolyte
Aluminium crust on electrolyte keeps heat in
Situated where there is a cheap supply of electricity
Why do people recycle aluminium
It is more energy efficient.
Recycling preserves stocks of ore
Create less waste
less residue from the purification process
less unused aluminium lying in land fill sites
