Transition metals: high melting point, dense, form coloured compounds, good catalysts e.g. iron
Corrosion: metals get oxidised.
To prevent rusting of iron:
Exclusion of oxygen and water: use paint, oil/ grease, plastic
Sacrificial protection: galvanise using a more reactive metal, which will rust first and prevent water and oxygen reaching the metal underneath
Exclusion of oxygen: keep in vacuum container
Exclusion of water: use a desiccant in the container (absorbs water vapour)
Electroplating: the surface of a metal is coated with a less reactive metal
Anode (positive): coating metal
Cathode (negative): original metal
Electrolyte: salt of the coating metal (as an aqueous solution)
Uses: prevents corrosion, nicer looking e.g. tin cans covering steel
Alloys: a mixture of two or more metals.
Alloys are harder than pure metals because they contain different sized particles so they don't slide easily when hammered.
Brass: 70% copper, 30% zinc.
Steel: 96% iron, with carbon, phosphorus, silicon and sulfur impurities.
Alluminium alloys with copper, manganese, sillicon: aircrafts as they light and strong e.g. magnalium.
Bronze: copper and tin
Gold alloys: less than 24 carat, the rest is copper or silver.
Chemical cell: produces a voltage until one of the reactants is used up
Hydrogen–oxygen fuel cell: hydrogen and oxygen are used to produce a voltage and water is the only product.
2H2(g) + O2(g) → 2H2O(l)
😄: no pollution, only waste is water, is rechargeable forever unlike batteries, quiet, efficient, continuous (will keep producing energy as long as fuel is supplied)
😦: expensive, difficult and expensive to store and transport hydrogen, dangerous? (too quiet)