C2.7 Electrolysis Flashcards
Define ‘electrolysis’
The breakdown of a substance containing ions by electricity.
Define an ‘electrolyte’
A liquid, containing free moving ions, that is broken down by electricity during electrolysis.
What 2 states must the electrolyte be in for electrolysis to work and why?
- Molten
- Dissolved in a solution
- So that the free ions can conduct the electricity
What happens at the anode (positive electrode)?
Electrons are taken away from ions (oxidation)
What happens at the cathode (negative electrode)?
Ions gain electrons that were taken away at the anode (reduction)
What is oxidation?
When electrons are lost from a substance (or when oxygen is added)
What is reduction?
When electrons are added to a substance (or when oxygen is removed)
Where is the metal produced in electrolysis?
At the cathode
Where is the non metal produced in electrolysis?
At the anode
What happens at the cathode if a salt is dissolved in water ?
- If the metal is more reactive than hydrogen, the metal ions and OH- ions will stay in the solution and hydrogen is produced.
- If the metal is less reactive than hydrogen, the metal will be produced and the H+ ions and OH- ions will stay in the water.
Why does the product formed at the cathode depend on its reactivity when a salt is dissolved in water?
If a metal is more reactive, it will be keener to stay as an ion to remain energetically stable.
What are the three useful products produced when sodium chloride solution undergoes electrolysis and their uses?
- Hydrogen
- Chlorine - used for bleach and plastics
- Sodium hydroxide - used for soaps
What type of solution is left behind when a salt is dissolved in water if the metal is less reactive than hydrogen?
A metal hydroxide solution
What is the half equation for the anode?
2(non metal)- ===> (non metal)2 + 2e-
What is the half equation for the cathode?
2(hydrogen/metal ion) + 2e- ===== (H2 or the metal)
What is the half equation of the anode for the electrolysis of sodium chloride solution?
2Cl ===> Cl2 + 2e-
What is the half equation of the cathode for the electrolysis of sodium chloride solution?
2H+ + 2e- ====> H2
What is the half equation of the cathode for the electrolysis of molten lead bromide?
Pb2+ + 2e- ====> Pb
How is aluminum manufactured?
By the electrolysis of a molten mixture of cryolite and aluminium oxide
What is the ore of aluminium?
Bauxite
What is produced at the anode during the electrolysis of aluminum?
Carbon dioxide - the oxygen formed at the anode reacts with the carbon the anode is made of.
What is the usefulness of cryolite during electrolysis?
- Aluminium oxide has a high melting point so melting it would be very expensive
- Dissolving it in molten cryolite brings the temperature down so it is easier and cheaper
Why do carbon electrodes need to be replaced often in the aluminum oxide electrolysis?
The carbon is used up when it reacts with the oxygen formed at the anode.
What is electroplating?
Coating the surface of one metal with another metal (e.g coating copper with silver)
What is the cathode in electroplating electrolysis?
The metal you want to plate
What is the anode in electroplating electrolysis?
The metal you want to plate the other with
What are two uses of electroplating?
- Decoration: silver is attractive but expensive, coating metals with it is cheaper than making things out of it.
- Conduction: metals like copper conduct well - they are used to plate metals for electronic circuits and computers
