Limestone and its uses
- We quarry large amounts of limestone because it has many uses.
- Limestone is a sedmentary rock.
- Chalk is an example of limestone.
- Limestone is corrosive and can be erroded by acid rain.
- Blocks of limestone can be used a building blocks. Limestone is used to make calcium oxide and cement (Made by heating limestone in a lime kiln with clay.)
- Concrete is made by mixing cement with water, sand and aggregate.
- Limestone is mainly calcium carbonate- CaCO3.
- When heated strongly calcium carbonate decomposes 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. Thermal decomposition means breaking down by heating.
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Reactions of Carbonates
- All metal carbonates react in similar ways when heated or when reacted with acids.
- Metal carbonates decompose to the metal oxide and carbon dioxide when they are heated strongly enough.
- A bunsen burner flame cannot get hot enough to decompose potassium carbonate or sodium carbonate.
- All carbonates react with acids to produce a salt, water and carbon dioxide gas. Limestone is damaged by acid rain because the calcium carbonate in the limestone reacts with acids in the rain.
- Calcium hydroxide solution is called limewater. Limewater is used to test for carbon dioxide. The limewater limewater turns cloudy because it reacts with carbon dioxide to produce insoluble calcium carbonate.
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The limestone reaction cycle
- When limestone (calcium carbonate) is heated strongly, it decomposes to give solid quicklime (calcium oxide) and carbon dioxide gas.
- When a small amount of water is added to the quicklime it gives slaked lime. (calcium hydroxide). Calcium hydroxide is an alkali and so it can be used to neutralise acids. For example, it is used by farmers to neutralise acidic soils and in industry to neutralise acidic gases.
- If a lot of water is added to the slaked lime a solution of limewater, or calcium hydroxide is formed.
- If carbon dioxide is bubbled through limewater, limestone is formed again, along with water.
- The thermal decomposition of calcium carbonate produces calcium oxide and carbon dioxide.
- Calcium oxide reacts with water to prodice calcium hydroxide.
- Calcium hydroxide is an alkaline that is frequently used to neutalise acids.
- Calcium hydroxide (Limewater) reacts with carbon dioxide to produce calcium carbonate.
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Cement and Concrete
- To make cement, limestone is mixed with clay and heated strongly in a kiln. The product of this reaction is then ground up to make a fine powder.
- Cement is mixed with sand and water to make mortar. Mortar is used to hold bricks and blocks together in buildings.
- Concrete is made by adding aggregate to cement, sand and water. Small stones or crushed rocks are used as aggregate. The mixture can be poured into moulds before it sets to form a hard solid.
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- We depend on Limestone to provide building materials. Cement and concrete are needed in most buldings.
- Quarrying limestone can have negative impacts on the environment and on people living near to the quarries.
- Cement works are often close to limestone quarries. Making cement involves heating limestone with clay in large kilns. This uses a large area of land and a lot of energy.
- Provide more jobs for local people
- More customers and trade for local businesses
- Improved roads
- Enough limestone is produced.Lots of products are made with limestone, such as toothpaste, make-up, and bread. It also makes glass, cement, concrete and mortar.
- Boasts local and national economy.
- Limestone quarries are very visible and ruin the environment. If the main source of income is tourism then the local economy could be damaged.
- Quarrying makes lots if noise.
- Creates heavy traffic.
- Loss of habitats for wildlife.
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