Electrolysis

• in covalent bonds, all the electrons on the outer shell are used to form it • this means that there are no mobile electrons that can carry a current as they are all used up • no mobile charge carriers means that no current can flow • so covalent compounds cannot conduct electricity

• in graphite, each carbon atoms forms 3 bonds to other carbons instead of 4 • this means that layers are produced • this leaves one free delocalised electron, which become mobile charge carriers and are free to move around the layers • this allows them to conducts electricity as a current can flow

• when solid, ionic compounds cannot conduct electricity as their ions are vibrating in fixed positions within the lattice • however, when molten or in aqueous solutions, the ions dissociate from each other and become free to move • this makes them mobile charge carriers as they are no longer in fixed positions so can carry a current • this means that ionic compounds can conduct electricity in molten or aqueous form

Cation

Anion

The process of splitting up a compound in either molten or aqueous form, into two new substances (elements) using electricity

• The conductor through which electricity is passed into and out of an electrolyte • often made out of carbon/graphite

The liquid that undergoes electrolysis; this is either molten of an aqueous solution containing mobile ions

Insoluble Ionic compounds have to be melted into a molten state in order to undergo electrolysis

as lots of energy is needs to melt an insoluble ionic compounds (as they have high melting points), substances such as cryolite can be added to the ionic compound to reduce its melting point. This means less energy is required to melt it = cheaper

• Loss of Electrons = Oxidation • Gain of Electrons = Reduction

Reduction and oxidation (so they are often called redox reactions)

Anode

Cathode

• once molten, if a lightlbulb is in circuit, it will light up as electrons start flowing • bubbling will occur around the anode due to formation of brown bromine gas, which may or may not be visible depending upon the scale of the experiment • no obvious change will be seen near cathode, but a lump of silver metal will have formed under once heating stops

• anion = bromide Br- (goes to anode) • cation = lead(II) Pb2+ (goes to cathode)

• cation = cathode • anion = anode

• molten state = ions move around freely • negative bromide ions attracted to anode (as opposite charges attract) • bromide ions become discharged and lose an electron to become bromine • they form bromine diatomic molecules to be stable • given off as bromine gas • electrons from bromide ions travel to cathode and are given to lead(II) ions • lead(II) ions become lead atoms by gaining 2 electrons • lead metal will deposit underneath cathode

Pb2+ (l) + 2e- => Pb (l)

2Br- (l) => Br2 (g) + 2e-

The ions in water (H+ and OH-) naturally dissociate from each other

• Na+ (from ionic compound) • Cl- (from ionic compound) • H+ (from water) • OH- (from water)

a gas would collect in the test tube over the cathode and the same would happen for the anode

• hydrogen is less reactive than sodium, so it is easier to add an electron onto it for it to be discharged • this means that hydrogen ions are attracted to the cathode and are given an electron • hydrogen ions become hydrogen molecules and hydrogen gas is given off • gas is collected in the inverted test tube above the cathode • halide ions (in this case Cl-) are preferentially attracted to anode instead of OH- ions • an electron is removed from chloride ion and become chlorine molecules + chlorine gas is given off and collected in the inverted test tube above the anode • the remaining ions (Na + and OH-) together form sodium hydroxide solution