key terms

• electrolysis = the breaking down of ionic compounds using electricity

• electrode = rods made of graphite or platinum

• anode = rod connected to the positive side of the battery

• cathode = rod connected to the negative side of the battery

• anion = the negative ion which is attracted to the anode

• cation = the positive ion which is attracted to the cathode

• electrolyte = liquid that is a good conductor of electricity

• electroplating= the process of adding a thin layer of a less reactive metal

• cryolite = substance which decreases the boiling point of bauxite from 2000˚- 900˚

-graphite and platinum are used because they are inert and good conductors

-metal is always the +ve ion

-non-metal is always the -ve ion

electrolysis of molten ionic compounds

cation → sodium (Na)

anion → chlorine (Cl)

electrolyte → molten sodium chloride (NaCl)

electricity passes and the sodium chloride (NaCl) is broken down.The positive sodium ion is attracted to the cathode where a reduction reaction takes place , the +ve sodium gains electrons and becomes a neutral sodium atom. Na+ + e- → Na. A shiny layer of sodium then forms around the cathode. The negative chlorine ion is attracted to the anode where an oxidation reaction takes place , the -ve chlorine loses electrons and becomes a neutral chlorine atom. Cl- - e- → Cl. Effervesence occurs and green bubbles are visible around the anode. the sodium extracted can be used in street lamps, salts and drugs whereas the chlorine can be used for bleaching and purification of water.

electrolysis of aqueus solution

cation → sodium (Na) or hydrogen (H)

anion → chlorine (Cl) or oxygen (O)

electrolyte → sodium chloride(NaCl) + water (H2O)

Hydrogen ion which is positive and less reactive than the sodium is attracted to the negative cathode.

→ concentrated solution

if the solution is concentrated then the negative chlorine (Cl) is attracted to the anode and sodium hydroxide (NaOH) is left in the electrolyte.

→ dilute solution

if it is dilute then the hydroxide (OH) is attracted to the anode and sodium chloride (NaCl) is left in the electrolyte.

electroplating

anode → metal used to plate item e.g - gold

cathode → item being plated e.g - ring

electrolyte → metal nitrate

The gold at the anode must be clean to allow even distribution of plating and to allow attraction to occur. the ring must be fully submerged into the electrolyte for full electroplating to occur, as only what is in the electrolyte is plated.The item at the cathode must be rotating so the metal covers the ring all around.

Electricity passes and dissolves the gold from the anode into the electrolyte where it forms gold nitrate the gold nitrate is broken down and the gold is attracted to the cathode ( ring ) and the nitrate stays in its place. The cathode gains gold atoms whereas the anode loses gold atoms.

extraction of aluminium using electolysis

anode → graphite

cathode → graphite

electrolyte→ cryolite

A steele container is lined with graphite which is attached to the -ve side of the battery making it the cathode, and three electrodes are connected to the +ve side of the battery making it the anode. Aluminium ore (molten bauxite) is added to the container with cryolite to complete the circuit. bauxite is molten due to the heat from electricity. The cryolite is used to save time money and electricity.

electricity passes and breaks down the bauxite into aluminium ion (Al+) and oxygen (O-). the aluminium is attracted to the cathode so it stays at the bottom of the container whereas the oxygen is attracted to the anode. the oxygen gas reacts with the graphite to produce carbon dioxide which diffuses into the air. o2 + c → co.

the graphite anodes need to constantly be changed because thier mass decreases due to its reaction with oxygen.

the aluminium extracted can be used for aeroplane bodies, cans and food containers because it has low density , resists corrosion and is a good conductor. akuminium is expensive becasue graphite rod used needs to be changed alot and because electricity used to extract it is expensive. lot of pollution is caused from extraction of aluminium due to the carbon dioxide which diffuses into the air.