Metals & other materials

5.1 Metals and acids

metal + acid → salt + hydrogen

Test for hydrogen: a lit splint gives a "squeaky pop".

The salt's name depends on the acid:

5.2 Metals and oxygen

metal + oxygen → metal oxide

e.g. magnesium burns in air with a bright white flame to form white magnesium oxide. This is an example of oxidation.

5.3 The reactivity series

Metals listed from most to least reactive (a useful chunk to memorise):

K, Na, Ca, Mg, Al, Zn, Fe, (H), Cu, Ag, Au

Hydrogen is included as a reference: metals above hydrogen react with acids; metals below it (Cu, Ag, Au) generally don't.

5.4 Metal displacement reactions

A more reactive metal will displace a less reactive metal from a salt solution.

5.5 Extracting metals

• Most metals are found in the Earth as ores (compounds with oxygen or sulfur, etc.).
• To extract them, you need to remove the oxygen — this is called reduction.
• Metals less reactive than carbon (Zn, Fe, Cu) can be extracted by heating with carbon — carbon takes the oxygen.
• Metals more reactive than carbon (Al, Mg, Na) need electrolysis — passing electricity through a molten compound. More expensive.
• Gold can be found as the metal itself ("native gold") because it's so unreactive.

5.6 Ceramics

• Made from clay or glass.
• Hard, brittle, electrical insulator, withstands high temperatures.
• Examples: pottery, bricks, glass, porcelain.

5.7 Polymers

• Long chains of repeating units (monomers) joined together.
• Generally flexible, light, and good electrical insulators.
• Examples: polythene, polystyrene, PVC, nylon.

5.8 Composites

• Made by combining two materials so the composite has properties of both.
• Examples: concrete (cement + sand + gravel), fibreglass (plastic + glass fibres), carbon-fibre (plastic + carbon fibres).
• Often light AND strong — used in bicycle frames, aircraft, sports gear.