Chemical changes

Chemical changes

Reactivity series

Ores are rocks from which it is economical to extract the metals it contains. Many metals in ores have been oxidised and must be reduced to be extracted. 

The reactivity series is a list of metals in order of their reactivity with water and dilute acid. The most reactive metals are potassium, sodium, and lithium; magnesium lies between lithium and copper.

When metals react with water or dilute acid, hydrogen is emitted, popping with a 'lighted' spill.

• When reacting with water, potassium, sodium, lithium, and calcium fizz, emitting hydrogen and leaving alkaline solutions of metal hydroxide.
• When reacting with dilute water, potassium, sodium, and lithium explode.
• When reacting with water, magnesium, aluminium, zinc, and iron react very slowly.
• When reacting with dilute water, calcium, magnesium, aluminium, zinc, and iron fizz, emitting hydrogen and forming salts.
• Tin and lead react slightly with steam and react slowly with warm acid.
• Copper, silver, and gold do not react.

Displacement reactions

Study tip: use the mnemonic 'OILRIG' which means Oxidation Is Loss, Reduction is Gain

A more reactive metal displaces a less reactive metal from an aqueous solution of one of its salts. These are called displacement reactions.

An ionic equation shows how atoms and ions change in a reaction. Ions that do not change are called spectator ions.

Hydrogen is positioned between lead and copper, while carbon is positioned between aluminium and zinc.

Oxidation is the loss of electrons but reduction is the gaining of electrons.

Half-equations show what happens to each reactant.

Extracting metals

Ores are mined from the ground and concentrated before purification and extraction. Unreactive metals are found in their native state. Whether extraction of the metal is worth it depends on:

• changing demands for the metal
• ease of extraction
• the amount of metal the ore contains

These factors change over time.

The extraction used depends on the position of the metal in the reactivity series. Carbon displaces less reactive metals from its compound when the metal is heated with carbon (reduction); metals more reactive than carbon are extracted by electrolysis of the molten compound. Hydrogen can be used to reduce metals because the metal obtained…