Electrolysis

Topic 4 - Chemical Changes

Electrolysis

=> Spitting up with electricity (separate the elements in ionic compounds)

Equipment

-> Beaker to contain the electrolyte (liquid solution containing the ionic compound; ions are free to move)
-> Electrodes; Cathode [-] and Anode [+] (solid conductors: metal or carbon)
-> Power supply (battery)

Experiment: Lead Bromide

-> melt insoluble solution so ions are free to move
-> the negative bromide ions [Br^-] are attracted to the positive electrode [anode], and will be discharged (turning from charged ions into neutral atoms) turning into bromine gas
-> the positive lead ions [Pb^2+] are attracted to the negative electrode [cathode], and will be discharged to form pure molten lead at the bottom of the beaker
-> electrons from the bromide ions are transported to the cathode from the anode by the wire (using power of the battery) and gives it to the lead ions

Experiment: Aluminium Oxide

-> after mixing it with cryolite to lower melting point, melt the bauxite to Aluminium Oxide [Al^2O^3]
-> Oxygen will be attracted to the anode and transfer their 2 extra electrons to the anode and discharge into oxygen molecules forming Oxygen gas [O^2]
-> their electrons go to the cathode
-> the positive aluminium ions will be at the cathode and each will take 3 electrons to form Al atoms (that forms at the bottom of the beaker to form molten Al metal)
-> 2O^2 => O^2 + 4e- [oxidised]
-> Al^3+ + 3e- => Al [reduced]

Aqueous Solutions [containing hydrogen and hydroxide ions]: Rules

Cathode:
-> the ion of the least reactive element will be the one that gets discharged (hydrogen or copper)

Anode:
-> if a halide is present (e.g. F, Cl, Br, I, At), it will be the one to get discharged
-> if a halide isn't present, it will always be the hydroxide ions that will be discharged