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Useful Products from Rocks (Higher)
 
Limestone | Cement, Concrete and Glass
 
Limestone

Limestone is a very useful type of sedimentary rock.

It is a naturally occurring form of calcium carbonate, CaCO3

Limestone is used as a building material.

In powdered form it can be added to lakes and soils to neutralise acidity, because it is a base.

When limestone is heated strongly in a kiln, it breaks down to quicklime (calcium oxide) and carbon dioxide.

calcium carbonate
—›

calcium oxide

+

 carbon dioxide
(limestone)
  

(quicklime)

    

This type of reaction is called thermal decomposition. Other carbonates also undergo thermal decomposition.

Quicklime reacts with water to produce slaked lime (calcium hydroxide).

Calcium oxide

+

 water

  —›

 calcium hydroxide

(quicklime)

       (slaked lime)

Slaked lime is also used by farmers to neutralise acidic soils.

 

Cement, Concrete and Glass

Cement is made by roasting powdered limestone with powdered clay in a rotary kiln.

When water is added to powdered cement, a series of chemical reactions take place to form a hard interlocking mass of crystals.

Concrete is made by mixing cement with water, sand and crushed rock.

A slow chemical reaction occurs which eventually forms hard, stone-like concrete that is used for building.

Reinforced concrete is made by allowing the concrete to set around steel rods. This makes it stronger.

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