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

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  • Created on: 15-05-15 17:58

Limestone and its Uses

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
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Limestone and its Uses (Continued)

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         

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Reactions of Carbonates

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.

 

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The 'Limestone Reaction Cycle'

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
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The 'Limestone Reaction Cycle'

The Limestone Reaction Cycle (Anticlockwise)

(http://www.donnamiele.com/Site/Armand/Entries/2008/1/24_The_Limestone_experiment_files/lime_cycle.gif)

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Cement and Concrete

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
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Limestone Issues

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
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