Limestone and it's uses
- Limestone is a rock that is mainly made of calcium carbonate.
- Powdered limestone can be heated with powdered clay to make cement. When we mix this with water, sand and crushed rock a slow chemival reaction takes place to make concrete.
- The chemical formula for calcium carbonate is CaCO3. It is made up of calcium ions (Ca2+) and carbonate ions (CO32-). The 2+ and 2- charges tell us that there are the same number of each (ions) in calcuim carbonate.
- When we heat limestone strongly, the calcium carbonate breaks down to form calcium oxide by Thermal decomposition.
- Calcium oxide is very useful in building and farming industries.
- To make lots of calcuim oxide we heat the calcium carbonate in a LIME KILN. We fill it with crushed limestones and heat it strongly by passing hot air through it. Waste gases leave at the top. The limestone slides acros the tilted kiln and is reacted by the time it reaches the other end where it is dropped out.
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Reactions of carbonates
- Things made of limestone suffer bad damage from acid rain. Limestone is calcium carbonate, which reacts with the acid.
- To test for carbon dioxide, you can put it through limewater and it turns cloudy. This is because limewater is a solution of calcium hydroxide and is alkaline. Carbon dioxide is a weakly acidic gas so it reacts with the alkaline limewater. This makes a precipitate of calcium carbonate, which is what turns it cloudy.
- Carbonates react with acids to give a salt, water and carbon dioxide.
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The limestone reaction cycle
- Limestone is used widely as a building material and to make other materials in the construction industry.
- 1. Calcium oxide is made when we heat limestone (calcium carbonate) very strongly.
- 2. When we add water to calcium oxide it produces calcium hydroxide.
- 3. We add more water and it becomes calcium hydroxide solution.
- 4. Then when we add carbon dioxide again it turns back into calcium carbonate.
- Calcium hydroxide is an alkali. It reacts with acids in a neutrilisation reaction. The products of the reaction are calcium, salt and water.
- It is used by farmers to improve soild that is acidic. Because it is alkali, it raises the pH of soil.
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Cement and concrete
- Lime mortar holds bricks together strongly, but it does not harden quickly, and will not set at all where there is water blocking it from carbon dioxide.
- Cement is made in industry by heating limestone with clay. It can be mixed with sand to produce mortar, used to hold building materials like bricks in place. An even stronger material is made by mixing cement, sand and aggregate to produce concrete. to make reinforces concrete, metal bars are mixed in too.
- 1. Cement = limestone + clay (heated in a kiln)
- 2. Mortar = cement + sand + water (mixing)
- 3. Concrete = aggregate + cement + sand + water (mixing)
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- Limestone is very useful but mining for it can affect the environment.
- It is quarried from the ground by blasting it with explosives, leaving a huge hole. Then it is taken in giant lorries to be processed. The blasting is bad because it leaves scars on the landscape and is very loud so, scares of wildlife, and annoys the people living nearby. The quarry gets filled with water, or becomes a landfill site.
- Bathroom tiles are usually made from ceramics with a glazed finish and are very hard wearing. Nowadays lots are made from travertine, which looks nice, but is easily scratched or damaged by acidic solutions (it is made of calcium carbonate)
- Mortar is used on building sites. There are two kinds- lime mortar and cement mortar. Lime takes a long time to set fully, especially in wet conditions. But when builders restore old buildings thy have to use lime because cement mortar is very strong and less flexible so it would make cracks along the old walls with barely any foundations.
- Manufacturig cement contributes about 5% of the carbon dioxide in the air, from burning fuels in the kilns. Lime mortar absorbs carbon dioxide as it sets, so would lead to less emissions.
- Concrete is the most popular building mateial and used to only be able to use a wire mesh to reinforce it, however now we can use: Glass fibres, Steel rods and even recycled paper. It is cheapeer to use reinforced concrete than steel, but it is less sturdy.
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