C1- Chemistry- C2.1 - 2.5 (Rocks and Building Materials)

Key Points

• Limestone is made mainly of calcium carbonate
• Limestone is widely used in the building industry
• The calcium carbonate in limestone breaks down when we heat it strongly to make calcium oxide and carbon dioxide. The reaction is called thermal decomposition
• We dig limestone out of the ground in quarries.

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Uses of Limestone

• Building materials
• Powdered limestone can be heated with clay to make cement
• Cement powder can be mixed with water, sand and crushed rock, a slow chemical reaction takes place

Heating Limestone

• Chemical formula for Calcium Carbonate = CaC03 
• Its made up of the Calcum ions Ca2+ and carbonate ions CO3^2- 
• The 2+ and 2- charges tells us that there are the same number of calcium ions and carbonate ions in calcium carbonate. The charges on ions cancel out in compounds
• When we heat limestone strongly, the calcium carbonate breaks down to form calcium oxide. Carbon dioxide is also produced in this reaction. 
• Breaking down a chemical by heating is called thermal decomposition

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Thermal Decomposition Equation

Word Equation-    Calcium Carbonate -->(heat) Calcium oxide + Calcium dioxide

Symbol Equation- CaCO3 --> CaO + CO2         

Key Points

• Carbonats react with dilute acid to form a salt, water and carbon dioxide
• Limewater turns cloudy in the test for carbondioxide gas. A precipitate of insoluble calcium carbonate causes the cloudiness
• Metal carbonates decompose on heating to form the metal oxide and carbon dioxide
• Magnesium, zinc, calcium and sodium decompose similarly. However not all carbonates decompose at bunsen temp.

Key Points

• Water + Calcium oxide = Calcium hydroxide (Word equation)
• H20 + Ca0 = Ca(OH)2 (Symbol equation)
• Calcium hydroxide is an alkaline so it can neutralise acids
• The reactions of limestone and its products that you need to know are shwon in the 'limestone reaction cycle'
• Calcium oxide is made when we heat limestone strongly. The calcium carbonate undergos thermal decomposition

The Limestone Reaction Cycle (Anticlockwise)

Key Points

• Cement is made by heating limestone with clay in a kiln
• Mortar is made by mixing cement and sand with water
• Concrete is made by mixing crushed rocks or small stones called aggregate, cement and sand with water

Key Points

• There are good and bad points about quarring for limestone. For example, more jobs will be created but there will be a large scar on the landscape
• Limestone, cement and concrete all have useful properties for use as building materials but the mining and processing of limestone and its products have major effects on our environment.

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Limestone Quarring

Advantages

• Creates Jobs
• Gives smaller food buisnesses customers from workers
• Ability to supply limestone doe the glass steel and cement industries

Disadvantages

• Noisy
• Horrible sight on landscape
• Destroys habitatats
• Distrubs residents