Electrolysis Flashcards
What is electrolysis?
The breaking down of a compound using electricity
Name of positive electrode
Anode ( as it attracts NEGATIVE anions)
Name of negative electrode
Cathode ( as it attracts POSITIVE cations)
What are electrodes usually made from
- Graphite (cheap)
- Platinum (expensive)
requirements for an electrode
- must be a solid that is conductive but inert (unreactive)
what is the electrolyte?
the substance to be broken down
-must conduct electricity
Why must the electrolyte be a molten or dissolved ionic compound or a metal?
- needs charged particles that are free to move
- ionic compounds have charged particles, but they are not free to come in a solid
why do covalent compounds not work for electrolysis
Do not have charged particles
Anomaly of covalent compound that can work in electrolysis
ammonia
What happens at anode in electrolysis of molten ionic compound?
non-metal ions lose electrons to form molecules (oxidised)
Half equation of electrolysis of molten MgCl2 (anode)
2Cl- -> Cl2 + 2e-
Half equation of electrolysis of molten MgCl2 (cathode)
Mg2+ + 2e- —> Mg
What happens at cathode in electrolysis of molten ionic compound?
metal ions gain electrons to form atoms (reduced)
observations at cathode
- solid (metal) formed
observations at anode
-effervescence due to gas formed
-(may be liquid in aqueous electrolysis as heat not required)
what happens to ions in water? (aqueous electrolysis)
water molecules can break apart (disassociate) and form H+ and OH- ions
Complications of aqueous electrolysis
- now 4 types of ion rather than 2 ( 2 positive, 2 negative), so must work out which is attracted to electrode and which remains in solution
How to decide which ion reacts at anode ( aqueous electrolysis)
- If halide ion ( Cl-/Br-/I-) is present, element is produced as normal at electrode
- otherwise O2 and H2O are produced
formula for O2 and H2O production at anode (aqueous electrolysis)
4OH- –> O2 + 2H20 + 4e-
how to decide which ion reacts at cathode ( aqueous electrolysis)
-If metal less reactive than Hydrogen, element produced as normal at electrode (gold, silver, copper)
- Otherwise, Hydrogen produced
formula for Hydrogen production at Cathode (aqueous electrolysis)
2H+ + 2e- —> H2
