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Science

Calcium carbonate

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Limestone is mainly calcium carbonate, CaCO3. When heated, it breaks down to form calcium oxide and carbon dioxide. Calcium oxide reacts with water to produce calcium hydroxide.

Limestone and its products have many uses: for example, in mortar, cement, concrete and glass.

Limestone, chalk and marble

Limestone, chalk and marble are all forms of calcium carbonate. They exist naturally in the Earth’s crust. Limestone is a very common building material and many tonnes are quarried in the UK every year. It is used for building - making concrete and cement - and the manufacture of glass, steel and iron.

Advantages and disadvantages of various building materials

Limestone, cement and mortar slowly react with carbon dioxide dissolved in rainwater, and wear away. This damages walls made from limestone, and it leaves gaps between bricks in buildings. These gaps must be filled in or "pointed". Pollution from burning fossil fuels makes the rain more acidic than it should be, and this rain makes these problems worse.

Concrete is easily formed into different shapes before it sets hard. It is strong when squashed, but weak when bent or stretched. However, concrete can be made much stronger by reinforcing it with steel. Some people think that concrete buildings and bridges are unattractive.

Glass is usually brittle and easily shattered, but toughened glass can be used for windows. While glass is transparent and so lets light into a building, the use of too much glass can make buildings very hot in the summer.

Uses of calcium oxide

Limestone can be broken down using heat to produce calcium oxide, which has lots of uses.

  • Add water and a vigorous exothermic [exothermic: Heat energy is released in an exothermic reaction. We know this because the surroundings get warm. ] reaction takes place. This forms calcium hydroxide.
  • Calcium hydroxide is soluble in water and forms a solution known as limewater which is used to test for carbon dioxide.
  • Calcium oxide, calcium hydroxide and calcium carbonate can be used to neutralise soil acidity.
  • Calcium carbonate can be used to remove acidic gases from coal-fired power station chimneys reducing harmful emissions and acid rain.

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