Metals and Non-metals
Metal extraction, reactivity and corrosion fill this domain. Expect questions on the reactivity series, why a metal is stored under oil, roasting versus calcination, ionic bonding, alloys and corrosion prevention.
Reactivity series
K, Na, Ca, Mg, Al, Zn, Fe, Pb, Cu, Hg, Ag, Au. A metal above another displaces it from its salt solution. Metals below hydrogen (Cu, Ag, Au) do not liberate H2 from dilute acids.
Extraction
- Sulphide ores are roasted in air: 2ZnS + 3O2 gives 2ZnO + 2SO2. Carbonate ores are calcined: ZnCO3 gives ZnO + CO2.
- Highly reactive metals (Na, K, Ca, Al) are obtained by electrolysis; moderately reactive ones by reduction with carbon.
- Thermite reaction: Fe2O3 + 2Al gives 2Fe + Al2O3 + heat, used to weld railway tracks.
Ionic compounds and corrosion
Ionic solids conduct only when molten or dissolved, because the ions must be free to move. Corrosion is oxidation of the metal; it is slowed by galvanising, painting, alloying or greasing. Brass is Cu + Zn, bronze Cu + Sn, stainless steel Fe + Cr + Ni + C.
Worked example
Zinc is added to copper sulphate solution. Zinc lies above copper in the series, so Zn + CuSO4 gives ZnSO4 + Cu; the blue colour fades and a red-brown deposit forms. Silver added to CuSO4 gives no reaction, because silver lies below copper and cannot displace it.
Traps
Swapping roasting and calcination; saying solid NaCl conducts electricity; forgetting that aluminium's oxide layer slows its reaction with CuSO4.