Electrolysis What

o It is the conduction of electricity by an electrolyte, an aqueous or molten ionic compound, leading to the decomposition of the electrolyte

Electrolysis of compoundso Molten

Evidence for the fact that ions are held in fixed position, in a lattice, when solid. But mobile when molten or aqueous, as electricity is conducted

Cations are attracted to the cathode (negative terminal) and get discharged, as they receive electrons

Anions are attracted to the anode (positive terminal) and get discharged, as they lose electrons

In electrolysis of a binary compound , ionic that only contain two elements, the two ions present are discharged, forming a metal and non-metal

o Aqueous Contains two electrolytes, the aqueous ionic compound and water A metal or hydrogen is discharged at the cathode A non-metal is discharged at the anode

Selective discharge (when using inert electrodes)o Cations

The least reactive metal ion gets preferentially discharged, as it gains electrons more readily

o Anions Easiest to hardest: Hydroxide, halides, nitrates and sulphates.

o Concentration effect When a halide solution is concentrated, the halides get preferentially discharged

compared to hydroxide Purification

o Purification of copper. Set-up

Pure copper cathode, impure copper anode Copper(II) sulphate electrolyte

Observations Cathode increases in size, anode decreases

o Copper forms at cathode, becomes ion at anode No colour change

o No net change in concentration of copper(II) ions Impurities are deposited below the anode

Electroplatingo It is the depositing a layer of metal on another substance using electrolysis

Nickolas Teo

o Set-up Object at cathode, metal electrode at anode Suitable metal electrolyte

o Uses Copper plating Tin plating of food cans

To prevent rusting Gold plating

Aesthetics reasons Simple cells

o What It is a device that converts chemical energy to electrical energy

Electrodes of different reactivity No source (battery)

o Electron flow The more reactive metal is the negative electrode and anode, hence electrons

flow more the more reactive to the less reactiveo Electrical energy produced

The bigger the difference in reactivity, more electricity is produced

Nickolas Teo