Chapter 17

 Which metals were discovered earliest?  Gold, copper, silver = less reactive metals  Found “native” ie. as pure metal  More reactive metals react with eg. oxygen in air  Found as compounds “minerals”  Have to be extracted from rocks “ores”  Then separated from their compound  Eg. very reactive metals are separated by electrolysis

Mineral: a metal compound found in the earth. Ore: a sample of rock which contains enough of the mineral to make extraction worthwhile What affects the price of a metal? How widely available it is and how much it costs to extract from rock samples.

 The method of extraction depends on the position of reactivity series.  When a more reactive metal replaces a less reactive metal in a compound  Some metals been used for longer than others through history due to the ease of extraction.

 Very reactive metals: K, Na, Ca, Mg, Al  Example: Aluminium Al 2 O 3 “alumina”is purified from ore bauxite (aluminium ore) Melting point of aluminium oxide = 2,072 o C Dissolved in molten cryolite. Cryolite lowers the melting point and makes the process cheaper.

Product at the cathode - Al 3+ (l) + 3e -  Al (l) Product at the anode - 2O 2- (l)  O 2 (g) + 4e - Carbon electrodes are used: they need to be replaced frequently as they react with the O 2 to form CO 2  wNEq14

Expensive process: lots of electricity used for electrolysis For heating the mixture Anodes erode and must be frequently replaced Extraction of bauxite and purification of aluminium oxide is costly environmentally Open cast mining Toxic sludge by-product

 Al is very low density  Al very unreactive (oxide layer on the outside)  Al good conductor  Aerospace, transport, power lines, drinks cans

 Metals below carbon in the reactivity series: Zn, Fe, Sn, Pb, Cu  The oxide is heated with carbon, which reduces the oxide and produces pure metal and CO 2.  Why can’t we use this method with metals above carbon in the reactivity series?  No reaction: carbon has to be more reactive in order to displace the metal.

3 raw materials: Iron (III) oxide is the source of iron Coke: source of carbon Limestone: removes impurities Carbon in coke reacts with O 2 in the air: CO 2 CO 2 reacts with more carbon from the coke to produce CO CO is the reducing agent: Fe 2 O 3 + 3CO → 2Fe + 3CO 2 The limestone reacts with the impurities and produces slag.

 Cast Iron  Strong and does not expand too much  Uses: car engine  Wrought iron  Softer, easy to work  Uses: gates, railings  Steel  Stronger  Wires, cables, bridges

Which metals rust? Only iron Formula of rust? Fe 2 O 3 xH 2 O: hydrous iron oxide How can rusting be prevented? Coating with paint or oil Alloys: stainless steel Galvanisation: coating with a zinc layer, sacrificial protection. Zn is more reactive so reacts instead of the iron