Limestone is a type of sedimentary rock that is mainly made up of a

substance called calcium carbonate.

Calcium carbonate has the chemical formula, CaCO3

Because it has many uses and can be used to make other products, limestone is a valuable

resource.

Basic properties of limestone

The appearance of limestone can vary tremendously.

Limestone is calcium carbonate and like any carbonate, it reacts with acids producing carbon dioxide gas.

bubbles of CO2

Carbon dioxide turns limewater milky.

Because it reacts with acids, it is sometimes added to lakes to remove acidity caused by acid rain.

Limestone is a sedimentary rock and most of it (especially chalk) was formed from the remains of tiny sea creatures.

Limestone, chalk and marble are all forms of calcium carbonate CaCO3.

Limestone Chalk Marble

This process took millions of years.

Limestone and chalk often contain fossils.

Where is limestone found in the British Isles?

limestone areas

There are also limestone cliffs on the coast in the Vale of Glamorgan

Sedimentary rocks at Llantwit Major in the Vale of Glamorgan

Layers of limestone and shale

fossils in the fallen limestone blocks

fossils from rocks on left

prepared specimen – a Jurassic oyster (180 million years old!)

More fossils found in limestone.

A Jurassic ammonite from North Yorkshire.

180 million years old.

A Silurian gastropod (snail) from Shropshire.

400 million years old.

Important uses of limestone

As a building material1.

Limestone has been used for thousands of years for buildings and roads.

However, since it is attacked by acids it is easily weathered and eroded.

2. For making glass

Glass is made by heating a mixture of limestone , sand and sodium carbonate (soda).

For making cement

Cement is made by heating together powdered limestone and clay in a rotary kiln.

Limestone and clay Rotating

kilnGas burners

Crusher

Cement

3.

Cement

mortar for joining bricks together

concrete for buildings etc.

Mix with sand and water

Mix with sand and water and chippings

Summary – the uses of limestone

Buildings and roads

Glass (heat with sand and sodium carbonate)

Neutralise acidic soils and lakes

Cement (heat with clay)

Mortar (cement + water + sand)

Concrete (cement + sand + gravel + water)

CaCO3

Limestone Quarrying

The quarrying of limestone can have major effects on the environment.

Limestone quarrying provides the raw materials for making many important substances such as glass and cement etc. It also provides employment for people and benefits the local economy.

But what exactly are the disadvantages?

Limestone Quarrying – some disadvantages

An ‘eyesore’ in areas of the countryside

Noise from blasting

Dust etc. from lorries

Loss of habitat for wildlife

Heating limestoneWhen limestone is strongly heated is begins to glow (limelight!)It decomposes to form calcium oxide (quicklime) and carbon dioxide gas.We can write a word equation:

calcium carbonate calcium oxide + carbon dioxide

or a symbol equation:

CaCO3 CaO + CO2

This type of reaction, where a substance is broken down by heat is called a THERMAL DECOMPOSITION

The thermal decomposition of limestone

Calcium oxide (quicklime) is produced industrially using a lime kiln

Limestone in

Hot air in

Kiln rotates to ensure that the limestone is mixed with the hot air

Air + carbon dioxide

Lime out

calcium carbonateheat

calcium oxide + carbon dioxide

A thermal decomposition reaction

a lime kiln

Adding water to quicklime

Calcium hydroxide solution is limewater which turns ‘milky’ with carbon dioxide.

We can write a word equation:

calcium oxide + water calcium hydroxide

CaO + H2O Ca(OH)2

When water is added to quicklime (calcium oxide), the reaction produces much heat and slaked lime (calcium hydroxide) is formed.

A reaction that produces heat is called an exothermic reaction.

or in symbols

‘slaking’ lime

Slaked lime (calcium hydroxide) also has uses:

to neutralise acidic soil

to make lime mortar (often used to restore old buildings

Heating other carbonates

A number of other carbonates are decomposed in the same way as calcium carbonate when heated e.g.

copper carbonate copper oxide + carbon dioxide

zinc carbonate zinc oxide + carbon dioxide

Both these reactions are again examples of a thermal decomposition.

heat

(green) (black)

CuCO3 CuO + CO2

(Zinc oxide is yellow when hot, white when cool)

heat

ZnCO3 ZnO + CO2