Extraction and Uses of Metals (2b)

Metal Ore

Rock that contains enough of a metal to make extraction profitable

Ways of Extracting Metals from Ores

• electrolysis

• blast furnace

• reacting with a more reactive material

• reduction: when ore is an oxide of the metal, since oxygen is being removed

Oxide Ores

• ex: Iron → Haematite; Aluminium → Bauxite

• extracted by reduction, since removal of oxygen

Unreactive Metals

• don’t have to be extracted chemically since found as an uncombined element

• because don’t react with other substances due to chemical instability

• ex: Au and Pt

A metal can reduce another metal only if it is ___________ than the metal that is bonded to the oxygen

more reactive

Extraction of Metals and Reactivity Series

• most reactive at the top

• tendency to become oxidised is linked to position

• higher up are less resistant to oxidation

• position determines method of extraction

Metals extracted by Electrolysis

• electrolysis of molten chloride or oxide

• large amounts of electricity required → expensive process

Metals

• K

• Na

• Ca

• Mg

• Al

Metals extracted by Reduction

• extracted by heating with a reducing agent like C or CO in a blast furnace

• cheap since C is cheap and can be used as a source of heat

Metals

• Zn

• Fe

• Cu

Metals found as Pure Elements

• Ag

• Au

Extraction of Iron from Haematite

• extracted in a large container called a blast furnace

• modern blast furnaces produce approx. 10,000 tonnes of Iron per day

• continuous process with raw materials added and removed all the time

• due to cost and time associated with getting the furnace up to temperature

Extraction of Aluminium from Bauxite

Electrolysis

• bauxite is purified to produce Al₂O₃

• this is dissolved in molten cryolite to lower melting point

• mixture is placed in an electrolysis cell made from steel lined with graphite

• graphite lining acts as cathode, large graphite blocks act as anode

• at cathode, Al ions get reduced, molten Al forms, gets siphoned off from time to time

• at anode, oxidation, oxygen produced → C reacts with O₂ to form CO₂

• anode wears away, has to be replaced

• expensive process

Electrolysis Half Equations

• Al³⁺ +  3e^–  → Al 

• 2O^2– → O₂ + 4e^–

• C (s) + O₂ (g)   →   CO₂ (g)

Aluminium Uses

• aircraft bodies (high strength-weight ratio)

• saucepans (very good conductor of heat, unreactive)

• overhead electrical cables (very good electrical conductor)

• food cans (non-toxic, corrosion and acidic food-stuff resistant)

Copper Uses

• electrical wiring (very good electrical conductor, ductile)

• saucepans (very good electrical conductor, malleable)

• water pipes (unreactive to water, non-toxic, malleable)

Steel Types

• mild

• high carbon

• stainless

Mild Steel

• Fe alloyed with 0.25% C

• used in car bodies and wiring

• soft and malleable

High Carbon

• Fe alloyed with 0.5 - 1.4% C

• used in car body panels and wiring

• hard

Stainless Steel

• Fe alloyed with 20% Cr and 10% Ni

• used in cutlery, sinks and chemical plants

• strong and corrosion-resistant

Alloys

Mixture of two or more metals with a non-metal like Carbon Ex: Steel

Alloy Properties

• stronger and harder

• resistant to corrosion

• resistant to extreme temperatures

this makes them more useful than pure metals

Alloys are harder because:

• contain different sized atoms

• this distorts atoms’ regular arrangements

• more difficult for atoms to slide over each other

Brass Composition

70% Cu, 30% Zn

Alloy Diagram