Electrolysis Flashcards
What is electrolysis
Electrolysis is the breakdown of a substance containing ions by electricity
What types of ionic compounds cannot conduct electricity
Solid ionic compounds cannot conduct electricity. This is because the ions are locked in place by strong electrostatic forces of attraction, in the giant ionic lattice structure, and are not free to move
what are the ions, in an ionic compound held in place by
Strong electrostatic forces of attraction
Describe what happens when an ionic compound is melted or dissolved in water
Explain what this now means?
When an ionic compound is melted or dissolved in water, the forces of attraction are broken and the ions are free to move and carry a charge.
Because the ions can now move, these liquids and solutions can now conduct electricity. These liquids or solutions are called electrolytes
In electrolysis what are the electrodes made from and why?
Graphite - conducts electricity and is inert (so it doesn’t react with the electrolyte)
Negative electrode
Positive electrode
names
Negative electrode - Cathode
Positive electrode - Anode
What is the cathode attached to
Cathode is attached to the negative terminal of the power pack/supply
Cathode is covered with___
cathode is covered with electrodes which are coming from the power pack
what is the anode connected to
Anode is connected to the positive terminal of the power pack/supply
anode is not covered with___
Anode has a lack of electrons
Describe what happens during the electrolysis of molten lead bromide
The positive lead (Pb2+) ions are attracted to the negative electrode (cathode) because opposite charges attract
At the cathode, the lead ions (Pb2+) gain two electrons to form Pb atoms (reduction)
(Pb2+ + 2e- —–> Pb)
Because lead ions are gaining electrons, lead ions are being reduced (an example of a reduction reaction)
The negative bromide ions (Br-) are attracted to the positive electrode (anode) because opposite charges attract
At the anode, the bromide ions (Br-) lose one electron to form Bromine atoms (oxidation)
(2Br- -2e- —-> Br2) - (br atoms pair to form a bromine molecule)
Because bromide ions are losing an electron, bromide ions are being oxidised (example of a oxidation reaction)
how do you extract metals that are less reactive than carbon
Metals that are less reactive than carbon, can be extracted by reduction with carbon
how do you extract metals that are more reactive than carbon
Metals that are more reactive than carbon, can be extracted by electrolysis
how is aluminium extracted
aluminium is extracted from the compound aluminium oxide by (using) electrolysis
Write the symbol equation for aluminium oxide
Al2O3
Another name for aluminium oxide
Alumina
What does aluminium oxide contain
It contains the aluminium ion (Al3+) and the oxide ion(O2-)
Uses of aluminium
pans
drink cans
aeroplanes
overhead power cables
cooking foil
window and patio door frames
bicycle frames and car bodies
Describe how aluminium is extracted by electrolysis
Aluminium is reduced (oxygen is removed) by decomposing it using electrolysis
For electricity to flow through the aluminium oxide, it must be molten (liquid)
Aluminium oxide has a very high melting point (around 2000 degrees celcius)
First, aluminium oxide is mixed with cryolite which lowers the melting point.
This reduces the amount of energy needed to melt the compound which saves money
Apply an electric current to the molten aluminium oxide.
The cathode and anode are both made of graphite (carbon) - it is a very good conductor of electricity, it has a very high melting point so it can be used at temperatures without melting
The aluminium ions (Al3+) and the Oxide ions (O2-) are free to move because this is molten aluminium oxide
The positive aluminium ions (Al3+ ions) are attracted to the cathode (the negative electrode) because opposite charges attract
At the cathode, each aluminium ion gains three electrons and forms an aluminium atom (this is reduction because aluminium ion has gained electrons - and reduction is the gain of electrons)
(these aluminium atoms sink to the bottom of the electrolysis tank)
Al3+ +3e- —–> Al
The negative oxide ions (O2- ions) are attracted to the positive electrode (anode)
At the anode, each oxide ion, loses two electrons to form an oxygen atoms (o2 gas molecules). because oxide ions are losing electrons, this is an example of oxidation reaction
Half equation to show the reaction at the anode: 2O2- -4e- —> 2O2
The anode must be replaced regularly.
Since the carbon (graphite) anodes are very hot they react with the oxygen molecules produced at the anode forming carbon dioxide gas
The carbon electrodes slowly burn away and so need replacing regularly.
C + O2 —> CO2
This is because the oxygen molecules produced at the anode react with the graphite (carbon) , forming carbon dioxide gas.
Explain why producing metals by electrolysis is expensive
Melting the compounds such as aluminium oxide requires a lot of energy
A lot of energy is required to produce the electric current
- explain why a mixture is used as the electrolyte - ELECTROLYSIS OF AL2O3
First, aluminium oxide is mixed with cryolite which lowers the melting point.
This reduces the amount of energy needed to melt the compound and saves money
explain why the positive eletrode must be continually replaced - electrolysis of AL2O3
The anode must be replaced regularly.
Since the carbon (graphite) anodes are very hot they react with the oxygen molecules produced at the anode forming carbon dioxide gas
The carbon electrodes slowly burn away and so need replacing regularly.
Write a half equation to show the reaction at the positive electrode
Anode - positive
2O2- - 4e- —> O2
2O2- ——> O2 + 4e -
Write a half equation to show the reaction at the negative electdode
Al3+ + 3e- —-> Al
Write the equation to show the reaction which causes the positive electrode to wear away
C + O2 —> CO2
overall equation for electrolysis of aluminium oxide
Aluminium oxide -> aluminium + oxygen
2Al2O3(l) —> 4Al(l) + 3O2(g)
why is aluminium expensive
High cost of electricity
Also high cost of heat and replacement electrodes
___________________
Melting the compounds such as aluminium oxide requires a lot of energy
A lot of energy is required to produce the electric current
