C3.3 Using resources · KS3 Science

The reactivity series

From most to least reactive: potassium, sodium, calcium, magnesium, aluminium, (carbon), zinc, iron, (hydrogen), copper, silver, gold.
Reactive metals react with water to make a metal hydroxide and hydrogen. Metal + acid → salt + hydrogen.
A more reactive metal displaces a less reactive metal from its compound: magnesium + copper sulfate → magnesium sulfate + copper.

Gold is so unreactive that it is found as the metal itself.
Metals less reactive than carbon (such as zinc, iron and copper) are extracted by heating their oxides with carbon. This is reduction: iron oxide + carbon → iron + carbon dioxide.
Metals more reactive than carbon (such as aluminium) are extracted by electrolysis, which uses a lot of electricity and is expensive.

Potable water is safe to drink. It isn't pure, because it contains dissolved salts.
Fresh water is treated by filtering it (through filter beds) and sterilising it (with chlorine, ozone or ultraviolet light) to kill microbes.
Desalination makes sea water drinkable by distillation or reverse osmosis, but it needs a lot of energy.
Testing water: check its pH, and evaporate a sample to see if solids are left behind. Pure water boils at exactly 100 °C.

Alloys, such as steel (iron and carbon) and brass (copper and zinc), are harder than pure metals, because different-sized atoms stop the layers sliding over each other.
Ceramics (pottery, glass) are hard but brittle; polymers (plastics) are light and flexible insulators; composites combine two materials, such as reinforced concrete or carbon fibre.
A life cycle assessment (LCA) looks at a product's environmental impact at every stage: getting the raw materials, making and packaging it, using it, and disposing of it. Some of the values are estimates, so LCAs can be biased.
Reducing, reusing and recycling saves raw materials and energy and cuts waste. Recycling aluminium uses far less energy than extracting it.
To judge a source of information, check who wrote it, whether it could be biased, whether it is based on evidence, and how recent it is.

Reactivity series: A list of metals in order of how reactive they are.
Displacement reaction: A more reactive metal taking the place of a less reactive metal in a compound.
Ore: A rock that contains enough metal to be worth extracting.
Reduction: Removing oxygen from a compound.
Electrolysis: Using electricity to break down a compound.
Potable water: Water that is safe to drink.
Desalination: Removing salt from sea water.
Alloy: A mixture of a metal with other elements, such as steel.
Polymer: A long-chain molecule; plastics are polymers.
Ceramic: A hard, brittle material such as pottery or glass.
Composite: A material made from two or more materials combined.
Life cycle assessment: An assessment of a product's environmental impact from start to finish.
Recycling: Processing used materials so they can be used again.