Electrolysis Flashcards
Define electrolysis
The process by which ionic substances are decomposed (broken down) into simpler substances (elements) when an electric current is passed through them
Where is electrolysis used?
It’s used for extracting metals from ores, purifying metals
What is an electrolyte? Why is it used?
A compound containing ions
It allows current to flow
Why can’t covalent substances act as electrolytes?
They do not contain electrons or ions to allow the current to flow
When does an ionic compound conduct?
When molten or dissolved (aqueous).
So the ions can move and carry charge
Covalent substances have
Low/high melting point?
Conduct, solid/liquid?
Dissolve and conduct in solution?
Low melting boiling point.
Does not conduct solid.
Does not conduct liquid.
Does not conduct in solution/insoluble
Is the anode positive?
👍
(Panic!
Positive is ANODE
Negative is cathode)
What are the electrodes made from?
Graphite
What process happens at the anode?
Two Cl- ➡️ Cl2+ 2e-
Lots of e-
Reduction
What process happens at the cathode?
Na2+2e- ➡️ Na
Gain of e-
Oxidation
What is a half equation?
Shows electron loss/gain
Therefore, oxidation/reduction
Written as e- ➡️ gained, go on the LHS
➡️ if lost go on the RHS
Why is a mixture of aluminium oxide, plus cryolite used as the electrolyte
Aluminium oxide,
melting point is 2000° C
Dissolved in cryolite
Melting point is 950° C
Less energy needed
Why does the positive electrode have to be replaced at regular intervals?
As oxygen is made at very hot temperatures carbon in the graphite reacts with the oxygen, causing it to wear away the electrode
C +O2 ➡️ CO2
Why is aluminium expensive?
High cost of electricity.
Cost of heat.
Cost of replacing anodes
In solution, small numbers of water, molecules ionised into H plus NH minus which are also attracted to the electrodes
This means that H2 may be formed at the cathode (from H+ ions), and O2 may be formed at the anode (from OH- ions)
