Electrolysis Flashcards
Electrolysis
Splitting of ions from their ionic compounds into their pure elements as atoms with no charge
Using electricity
What must we use in electrolysis?
A liquid ionic compound as molten or dissolved in water
Because only then can they conduct electricity and transfer electrons
Electrolytes
Liquid ionic compound which can conduct electricity
Cathode
Negative electrode covered in electrons from the power pack
Anode
Positive electrode with no electrons from the power pack
What happens in electrolysis of a molten solution?
Positive metal ions are attracted to the cathode and gain electrons to form metal atoms (reduced)
Negative non metal ions are attracted to the anode and lose electrons to form non metal atoms (oxidised)
Why do we use electrolysis for extraction?
If it’s more reactive than carbon so cannot be displaced from its oxide compound
Including aluminium
Where is aluminium extracted from?
Aluminium oxide using electrolysis
Aluminium oxide
Aluminium ions Al³⁺
Oxide ions O²⁻
How do we turn aluminium oxide into a liquid?
Mix with cryolite to lower its melting point so it can become liquid easier
Why do we use cryolite with aluminium oxide?
Because by lowering its melting point we use less energy to melt it therefore save money
What are electrodes made of in molten electrolysis and why?
Graphite
Because it’s made of a giant carbon structure
Can conduct electricity as it has delocalised electrons
High melting point
What happens at the cathode in electrolysis of aluminium oxide?
Al³⁺ + 3e- ——> Al
Reduced = gains electrons
What happens at the Anode of electrolysis in aluminium oxide?
2O²⁻ ——> O₂ + 4e-
Oxidation
Why must the anode be replaced regularly
Because oxygen molecules produced at anode react with carbon on surface of electrode to form CO2 = slowly wearing away the electrode
Why is electrolysis expensive?
High energy costs:
Lots required to melt the compound
Lots required to produce the electric current
What other ions are present in the electrolysis of aqueos solutions?
H+ ions
OH- ions
These are what water molecules ionise into
In an electrolysis of aqueous solution what forms at the cathode?
If the metal is less reactive than hydrogen = metal discharged
If metal is more reactive than hydrogen = hydrogen discharged
In electrolysis of aqueous solution what forms at the anode?
If the ionic compound contains a halogen the halide ion is discharged
If not oxygen is discharged
(Water is too but water already in the solution)
What material do we use for the electrodes in aqueous electrolysis?
Platinum as its inert and unreactive
So it doesn’t react with stuff easily
Electrolysis of aqueous solution anode half equation if a halogen ion isn’t present
4OH- ——> O₂ + 2H₂O + 4e-
Oxidation
If a halogen isn’t present in electrolysis of aqueous solution why don’t we say water is discharged?
Because water is already in the solution
We just point out oxygen
Electrolysis of aqueous solution if the metal is more reactive than hydrogen half equation
2H+ + 2e- ——> H₂
Reduction
