Chemistry-Rocks and building materials

Limestone and its uses

• Limestone is made mainly of calcium carbonate CaCO3
• Limestone is used as a building material and ot make calcium oxide and cement 
• Cement mixed with sand, aggregate and water makes concrete
• Calcium carbonate decomposes when heated to make calcium oxide and carbon dioxide. This is done on a large scale in lime kilns. The equation for this reaction is:
• Calcium carbonate       Calcium oxide + carbon dioxide 
• CaCO3                        CaO                  CO2
• This type of reaction is called thermal decomposition

Reactions of carbonates

• Metal carbonates decompose when heated to produce the metal oxide and carbon dioxide
• Carbonates react with acids to produce a salt, water and carbon dioxide
• Carbon dioxide turns limewater cloudy

The "Limestone reaction cycle"

• Thermal decomposition of calcium carbonate produces calcium oxide and carbon dioxide
• Calcuim oxide reacts with water to produce calcium hydroxide
• Calcium hydroxide is an alkali that can be used to neutralise acids
• Calcium hydroxide reacts with carbon dioxidr to produce calcium carbonate
• Steps:
• Step 1: Calcium carbonate- heat- carbon dioxide is given off and calcium oxide
• Step 2: Add a little water to the calcium oxide- calcium hydroxide
• Step 3: *** more water and filter- make calcium hydroxide solution
• Step 4: Add carbon dioxide ( this is the test for CO2)- makes calcium carbonate

Cement and concrete

• Cement is made by heating limestone which clay in a kiln
• Mortar is made by mixing cement and sand with water
• Concrete is made by mixing aggregate with cement, sand and water

Limestone issues

• There are good and bad points about quarrying for limestone 
• Limestone, cement and concrete are needed as building materials
• Quarrying and processing limestone and its products have negative impacts on the environment
• Advantages:
• More employment opportunities for local people
• More customers and trade for local businesses
• Improved roads
• Disadvatages:
• Dust and noise
• More traffic
• Loss of habitats for wildlife