Electrolysis Flashcards
What is electrolysis?
breakdown of an ionic compound (when molten or in aqueous solution) by passage of electricity
What is an electrolyte?
Aqueous solution of ionic substance or molten ionic salt
Why does an electrolyte conduct electricity?
Conducts electricity due to the presence of mobile ions
What are electrodes?
Rods which help current enter the electrolyte
What are the products formed from the electrolysis of Molten lead(II) bromide?
At cathode: lead
At anode: bromine
What are the products formed from the electrolysis of Concentrated hydrochloric acid?
At cathode: Hydrogen
At anode: chlorine
What are the products formed from the electrolysis of Concentrated aqueous sodium chloride?
At cathode: hydrogen
At anode: chlorine
What is formed at the cathode?
Metal/Hydrogen
What is formed at the anode?
Non-metal/Oxygen (OH-)
What is electroplating?
Coating one metallic object with another metal using electrolysis
What are the materials needed for electroplating? (3)
Anode made of metal you want to electroplate object with
Ions of same metal as anode in solution
Object to be plated at cathode
What are the uses of electroplating? (3)
Improving metal appearance
Galvanise
Prevent corrosion
Why is aluminum used for electricity cables? (4)
Light
Non-corrosive
Good conductor
Cheaper than copper
Why is copper used in electrical wiring? (2)
Good conductor
Ductile
Why are plastics & ceramics used as insulators?
Don’t conduct electricity
Conduct heat poorly
How is copper purified?
By using an impure copper anode and a pure copper cathode
Using inert electrodes
What are the materials needed for the purification of copper with copper electrodes?
Anode: Impure copper
Cathode: Pure copper
Copper sulfate solution
What happens during electrolysis using copper electrodes?
the metal atoms at the anode lose electrons to form positive ions
What are the materials needed for the purification of copper with inert electrodes?
Inert anode: Graphite
Inert cathode: Graphite
Copper sulfate solution
What happens during electrolysis using inert electrodes?
Negative ions in the electrolyte lose electrons to anode
What happens at the anode?
Reduction of positive ions
What happens at the cathode?
Oxidation of negative ions
What is the main ore of aluminum?
Bauxite
What are the electrodes used in the extracting aluminum made of?
Carbon
What is the electrolyte in the cell?
molten aluminium oxide dissolved in molten cryolite
Why is aluminum oxide dissolved in cryolite?
Decrease melting point, improve conductivity
Describe the process of extracting aluminium
1) Bauxite treated w/ sodium hydroxide to form sodium aluminate and heated to form aluminum oxide
2) Aluminum oxide dissolved in cryolite
3) Electrolysis using carbon electrodes
4) At cathode aluminum ions gain electrons, reduced to aluminum
5) At anode, oxide ions are oxidised to oxygen
6) Oxygen reacts w/ carbon
What are the products in extracting aluminum?
At cathode: aluminum
At anode: oxygen
What is brine?
Concentrated aqueous solution of sodium chloride
Identify the ions present in brine (4)
Na+ , Cl-, H+ and OH-
Where is brine electrolyzed?
In a diaphragm cell
What are the products electrolysis of brine? (3)
At cathode: Hydrogen
At anode: Chlorine
Sodium hydroxide forms in solution
What are the uses of chlorine? (2)
- treating drinking water
- making bleach
What are the uses of hydrogen? (2)
- making ammonia
- making margarine
What is the use of sodium hydroxide?
soap
Explain ionic movement in electrolysis
- In a molten ionic compound, ions able to move
- When current applied, cations move towards cathode - anions move towards anode
- Cations reach cathode and gains electrons (reduction)
- Anions reach anode and lose electrons (oxidation)
Where does reduction occur?
Cathode
What is copper refining?
When copper is purified by electrolysis
In copper refining, what electrodes are used?
Anode: Impure copper
Cathode: Pure copper
During electrolysis using inert electrodes, what happens to the negative ions in the electrolyte?
They lose their electrons to the anode
In copper refining using inert electrodes, why does the eletrolyte lose its blue colour?
Copper ions in solution are turning into copper atoms at the cathode
In copper refining using 2 copper electrodes, what happens to the anode?
As the anode is not inert, it loses electrons and copper ions go into solution - anode gets smaller
In copper refining using 2 copper electrodes, why does the electrolyte remain the same deep blue colour?
Copper ions removed from solution at cathode are replaced in solution by copper ions formed at the anode - going in to solution
What is the overall equation for the electrolysis of aluminium oxide using electrolysis?
2Al2O3 => 4Al + 3O2
