Chemistry: C3 ocr 21st century Science

Module C3 : Chemicals in our lives - risks and benefits

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  • Created on: 30-04-12 13:10

Minerals in Britain

The outer layer of the Earth has the ability to move. Scientists try to map this movement using a range of clues offered by the Earth. Many of the clues are found in the rocks themselves.

Tectonic plates:The outer layers of the Earth (the crust and upper part of the mantle) are divided into massive portions of rock called tectonic plates. These plates fit together like a jigsaw puzzle.

Differences shown in rocks: The movement of continents has meant a wide range of rocks are found in Britain that has formed in different climates.

The study of sedimentary rock provides evidence of the conditions under which they were formed.

  • fossils of plants and animals found in the rock are distinctive of certain geological time periods. Comparing them against modern day organisms gives an idea of the environment in which they existed
  • grains of sand found in rock can be compared against grains found in deserts or rivers to determine if they were air blown or water borne
  • ripples in rocks formed by wind blowing or water flowing.
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The Importance of Salt

What is commonly referred to as salt is the compound sodium chloride. It has long been important in the food industry as a preservative and also to add flavour. Another common use is to treat icy roads in winter as salty water has a lower freezing point then pure water.

Salt can be obtained from the sea or from underground salt deposits.

  • Mining - Large earth moving equipment is used to extract rock salt. This method of extraction leaves the salt with insoluble impurities such as reddish clay. This kind of salt is used to put on roads during freezing weather and does not need to be pure.
  • Solution in water - when pure salt for industrial purposes is needed a different method is used. Water is forced down a borehole into rock. The salt dissolves making a solution of brine and this solution is withdrawn to the surface and pumped to a purification plant. Water is evaporated from the brine under a range of pressures making the process more efficient. The salt crystallises and is separated from any remaining brine by filtering or using a centrifuge.

Environmental Impacts: Extracting salt in solution can create large underground caverns. This can lead to bedrock collapsing and as a consequence, cause the lowering of the Earth’s surface. This is known as subsidence. It can be avoided by sensibly spacing out the holes created so the surface is supported by a sufficient amount of rock underground.

Risks of salt: Salt (sodium chloride) is used in foods as a flavouring and preservative. Humans need sodium in their diet to allow the body to carry out essential functions. The main sources of salt in our diet are processed meats and fish, cereal products and some dairy products.

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