Using Limestone and Thermal Decomposition

The chemical name for limestone is                     calcium carbonate (CaCO3)

Limestone has many different uses, such as for concrete, cement and glass.

It can also be chemically changed into slaked lime and quicklime.

Limestone can be thermally decomposed to produce calcium oxide (CaO, also known as quicklime)

Thermal decomposition is when a substance is heated strongly to produce at least two products.

In this case, we are heating a carbonate, which means that the products will be a metal oxide and carbon dioxide. When limestone is heated:

Limestone = quicklime + carbon dioxide             CaCO3     =   CaO       + CO2

We create slaked lime by adding water to quicklime.

Chemical name for slaked lime is calcium hydroxide, Ca(OH)2.

Slaked lime can be used neutralise acidic soil, or lakes that are acidic due to acid rain. Slaked lime can also be mixed with sand and water to create mortar.

If we dissolve a little slaked lime in water, we create lime water, used to detect carbon dioxide. It turns cloudy when carbon dioxide is bubbled through it, this is because calcium carbonate (limestone) is formed, which is insolube in water:

calcium hydroxide + carbon dioxide = calcium carbonate + water

Cement can be created by heating powdered limestone with powdered clay in a kiln.

Concrete is created by adding stones or crushed rock to a mixture of water, cement and sand. When this sets it becomes very hard. However, concrete can be reinforced by pouring it around metal bars, which means that it will not crack as easily.

Glass is created by mixing powdered limestone with sand and sodium carbonate, and then heating it very strongly.

1. Limestone provides us with things that we need, such as roads and houses. Chemicals used in dyes, paints and medicines also come from limestone.

2. Slaked lime can be used to neutralise acidic soil and lakes. Powdered limestone can be used, but slaked lime is faster.

3. Limestone can be used in power station chimneys to neutralise sulphur dioxide, which is a cause of acid rain.

4. Quarrying can provide jobs for people, and give the local economy more money, leading to better roads, transport etc.

5. Limestone is widely available, and cheaper than marble or granite. It is also quite easy to cut.

6. Some limestone is more hardwearing than marble, but still attractive.

7. Concrete is a very cheap way of constructing buildings.

8. Glass is transparent, so useful for windows.

9. Limestone, concrete, cement and glass, don't rot when they get wet, they're fire resistant and can't be chewed by insects.

10. Concrete doesn't corrode like many metals do.

1. Quarrying ruins the landscape, makes lots of noise and dust, destroys habitats of animals, causes pollution due to transport and the waste causes ugly tips.

2. Cement factories produce a lot of dust which causes breathing problems for some people.

3. Energy is needed to create cement and quicklime, which most likely comes from fossil fuels and causes pollution.

4. Concrete is an ugly building material.

5. Glass can easily break into sharp pieces.