Metals react by losing electrons to form positive ions. The more easily a metal does this, the more reactive it is. Listing metals from most to least reactive gives the reactivity series (carbon and hydrogen are put in for comparison):

1. potassium, sodium, lithium, calcium, magnesium, aluminium
2. (carbon)
3. zinc, iron, tin, lead
4. (hydrogen)
5. copper, silver, gold

• With cold water: the metals at the top (potassium, sodium, lithium, calcium) fizz and give a metal hydroxide and hydrogen. Magnesium barely reacts; the rest do not react.
• With dilute acid: metals above hydrogen fizz, giving a salt and hydrogen. The higher the metal, the faster the fizzing and the bigger the temperature rise. Copper, silver and gold do not react.

In an experiment, "more reactive" shows up as more bubbles, a bigger temperature rise or a shorter time for the metal to disappear. A shorter time means a faster reaction, so sort times smallest first.

A more reactive metal pushes a less reactive metal out of a solution of its compound. The more reactive metal ends up in the compound.

magnesium + copper sulfate → magnesium sulfate + copper
Mg + CuSO₄ → MgSO₄ + Cu

You see the blue colour fade, a brown coating of copper, and the mixture gets warm. Copper placed in magnesium sulfate solution does nothing: a less reactive metal cannot displace a more reactive one.

If you have a grid of results, count how many other metals each one displaces: the metal that displaces the most is the most reactive.

Oxidation is gain of oxygen. Reduction is loss of oxygen. They happen together:

1. iron oxide + carbon → iron + carbon dioxide
2. iron oxide loses oxygen: it is reduced
3. carbon gains oxygen: it is oxidised

Most metals are found in ores as oxides. How a metal is extracted depends on where it sits compared with carbon:

• Below carbon (zinc, iron, tin, lead, copper): heat the oxide with carbon. Carbon takes the oxygen.
• Above carbon (aluminium and the metals above it): carbon cannot reduce the oxide, so electrolysis of a molten compound is used. That costs much more.
• Gold is so unreactive that it is found as the metal itself.

To find the mass of metal in an oxide, work out what fraction of the formula mass is the metal:

1. Fe₂O₃: Mr = 2 × 56 + 3 × 16 = 160
2. fraction that is iron = 112 ÷ 160
3. iron in 50 tonnes of Fe₂O₃ = 50 × 112 ÷ 160 = 35 tonnes

Use 2 × 56 for Fe₂O₃, not 56: count every metal atom in the formula.