Materials from the earth

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Rocks and their formation

Rocks make up the earths crust

Igneous rocks:

  • formed when magma/lava solidifies
  • made of interlocking crystals- makes them hard and resistant to erosion
  • have small crystals if liquid rocks cools quickly (e.g. basalt)
  • have large crystals if liquid rock cooled slowly (e.g. granite)

Sedimentary rocks:

  • formed when layers of sediment are compacted over a long period of time
  • erode more easily than igneous and metamorphic rocks
  • made of rounded grains and may contain fossils
  • include chalk and limestone (natural forms of calcium carbonate)

Metamorphic rocks:

formed from existing rocks by action of heat and/or pressure, causing new interlocking crystals. E.g. marble which is formed from chalk or limestone.

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Limestone and its uses

  • Limestone used for making buildings and as base for roads and railways
  • Mostly made of calcium carbonate which is an important raw material for making glass, cement and concrete
  • Limestone heated when making cement and glass. Heat decomposes the calcium carbonate in it to form calcium oxide and carbon dioxide. (Thermal decomposition)

Quarrying

  • We need to quarry a lot of limestone, but quarrying has ecenomic, enironmental and social effects.
  • We need to balance the effects with the demand.
  • (Advantages and disadvantages on separate page)
  • When heated strongly, calcium carbonate decomposes to form calcium oxide and carbon dioxide.
  • The word equation for the decomposition of calcium carbonate is:
    •  calcium carbonate à calcium oxide + carbon dioxide
    •  CaCO3 à  CaO + CO2
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Chemical reactions

  • Atoms are the smallest particles of an element that can take part in chemical reactions
  • During chemical reactions atoms are neither created nor destroyed
  • During chemical reactions atoms are rearranged to make new product with different properties from the reactants
  • The total mass before and after a reaction in a sealed container is unchanged (shown practically by a precipitation reaction)

Reactions of calcium compounds

  • When water is added to calcium oxide a lot of heat is released making the water boil and steam. It also fizzes.
  • Calcium hydroxide dissolves when more water is added forming calcium hydroxide solution (known as limewater)
  •  Calcium oxide, calcium hydroxide and calcium carbonate can be used to neutralise soil acidity. Farmers spray them over the fields to reduce the acidity of the soil.
  • Wet powdered calcium carbonate is sprayed through waste gasses from coal-fired powered station chimneys, this reacts with the acidic gases and neutralises them. This reduces harmful emissions and helps to reduce acid rain.
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