Metals
Properties and uses of metals and alloys, the reactivity series, extraction of iron and aluminium, and rusting.
📌 Key points
- Metals are good conductors of heat and electricity, malleable, ductile and usually have high melting and boiling points.
- Reactivity series (most to least reactive): potassium, sodium, calcium, magnesium, aluminium, (carbon), zinc, iron, (hydrogen), copper, silver, gold.
- Potassium, sodium and calcium react with cold water to give a hydroxide and hydrogen; magnesium reacts with steam to give magnesium oxide and hydrogen; metals above hydrogen react with dilute acids to give a salt and hydrogen.
- A more reactive metal displaces a less reactive metal from a solution of its salt or from its oxide.
- Aluminium seems unreactive because it is covered by a protective layer of aluminium oxide.
- Alloys are mixtures of a metal with other elements, e.g. brass (copper and zinc) and stainless steel (iron with chromium, nickel and carbon). Alloys are harder and stronger because atoms of different sizes stop the layers sliding easily.
- Uses: aluminium for aircraft (low density) and food containers (resists corrosion); copper for electrical wiring (good conductor, ductile); stainless steel for cutlery (resists rusting).
- In the blast furnace: C + O2 → CO2; CO2 + C → 2CO; Fe2O3 + 3CO → 2Fe + 3CO2. Limestone decomposes to calcium oxide, which reacts with silicon dioxide to form slag (CaSiO3).
- Aluminium is extracted by electrolysis of aluminium oxide (from bauxite) dissolved in molten cryolite, which lowers the operating temperature. The carbon anodes burn away in the oxygen produced and must be replaced.
- Rusting of iron needs both water and oxygen. It is prevented by barrier methods (paint, grease, plastic) or by galvanising: a zinc coating gives sacrificial protection because zinc is more reactive than iron.
📖 Key terms
- Alloy
- A mixture of a metal with other elements.
- Ore
- A rock containing a metal compound from which the metal can be extracted.
- Reduction
- Removal of oxygen from a compound (or gain of electrons).
- Rust
- Hydrated iron(III) oxide, formed when iron reacts with water and oxygen.
- Galvanising
- Coating iron or steel with a layer of zinc.
- Sacrificial protection
- A more reactive metal corrodes instead of the iron it is attached to.
- Slag
- Calcium silicate, formed in the blast furnace from the impurities in the iron ore.
✏️ Worked example
Magnesium ribbon is put into blue copper(II) sulfate solution. Describe and explain what happens and write the equation.
- Magnesium is more reactive than copper, so it displaces copper from the solution.
- Observations: a pink-brown solid (copper) forms and the blue colour of the solution fades.
- Word equation: magnesium + copper(II) sulfate → magnesium sulfate + copper.
- Symbol equation: Mg + CuSO4 → MgSO4 + Cu. Magnesium is oxidised (Mg → Mg2+ + 2e−).
Metals above carbon in the reactivity series must be extracted by electrolysis; metals below carbon can be extracted by reduction with carbon.
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