How were rocks made?
- The Outer layer of the earth is made up of 12 Tectonic plates.
- Convection currents under the plates make them move.
- Scientists use magnetic clues in rocks like Magnetite to track continents' movements.
- These processes form rocks:
- Sedimetation and Compression - Limestone when remains of dead sea animals fell to the bottom of warm seas near the equator.
- Erosion of rocks by rivers formed sand, this was deposited in layers to form Sandstone.
- Evaporation of seas formed Rock salt. Salty water was orginally salts from rocks dissolved in water flowing over them.
- Mountain building pushed coal towards the surface- the coal formed when plants in swamps died and were compressed and heated.
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How do we know how rocks were made?
- Different Animals lived at different times, their Fossils tell of the age of the rocks they are in.
- Comparing Sand grains in Deserts and Rivers to those in Sandstone tell what sort of sand formed the stone.
- Shapes of Ripples in rocks give clues about whether Sandstone was from River bed or Desert sand.
- Shell Fragments in Limestone tell of the conditions when the rock formed.
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Where does salt come from?
- Salt (Sodium Chloride) is used in Food, to Treat icy roads and in Chemical Synthesis.
- Salt for Foods must be Pure. Some of it comes from the Sea; water Evaporates, leaving salt behind.
- Rock salt - A Mixture of Salt and Clay. Used for de-icing roads, need not be Pure. It's mined from Underground with big machines.
- Salt for Chemical Industry must be Very Pure. It's obtained from Solution Mining: water pumped into Rock salt, salt Dissolves in water, Solution pumped to surface, Solid salt is Extracted from the solution.
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Why is Salt added to Food?
- Flavouring - Improves flavour of the food.
- Preservative - Stops food going off.
- Eating too much salt can raise your Blood Pressure; this increases the risk of a Stroke or Heart attack.
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Why are Alkalis useful?
- Before industrialisation, they were used to:
- Neutralise acid soil.
- Make chemicals to Bind dyes to cloth.
- Convert Fats and Oils into Soaps.
- Make Glass.
- Alkalis dissolve in water to form solutions of Ph above 7.
- They react with acids to form Salts:
- Sodium Hydroxide + Hydrochloric acid = Sodium Chloride + Water
- Alkalis include soluble Hydroxides and soluble Carbonates.
- Soluble Hydroxides react with acids to form a Salt and Water
- Sodium Hydroxide + Sulfuric Acid = Sodiumm sulfate + Water
- Soluble Carbonates react with acids to make a Salt, Water and Carbon Dioxide
- Sodium Carbonate + Hydrochloric acid = Sodium chloride + Water + Carbon dioxide.
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How were Alkalis obtained?
- Pre-Industrial Revolution - From burnt wood and stale urine.
- Industrial revolution - New way invented to make Alkali on a large scale.
- Raw materials: Salt (Sodium Chloride), Limestone (Calcium carbonate) and Coal.
- Made huge amounts of pollutants: Acidic Hydrogen Chloride gas, Solid waste which emitted toxic, smelly Hydrogen sulfide gas.
- Henry Deacon used Hydrogen chloride to make Chlorine by Oxidising it.
- Hydrogen chloride + Oxygen = Chlorine + Water.
- Chlorine is used as a bleach and to whiten paper and textiles.
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Why add Chlorine to Water?
- Chlorine kills pathogens in water.
- Adding Chlorine to Water leads to fewer deaths from waterborne diseases.
- Disadvantage: When Chlorine reacts with organic matter THMs may form and people think that drinking water containing these can cause cancer.
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What does Brine make?
- Passing electricity through brine (sodium chloride solution) causes chemical changes.
- The elements in Sodium chloride and Water are rearranged to form new products.
- Chlorine gas - Used to treat water, make bleach, plastic and Hydrochloric acid.
- Hydrogen gas - A fuel, make Hydrochloric acid.
- Sodium hydroxide solution - Used to make soap, paper and bleach.
- If the electricity is generated from fossil fuels, much pollution results.
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Are chemicals risky?
- There are 12 synthetic chemicals which are banned because everyone agrees that they are harmful evem in small amounts.
- They cause problems because:
- They don't break down in the environment.
- They travel long distances in the air and in water.
- They build up in the fatty tissue of animals and humans.
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What are the dangers of PVCs?
- PVC molecules are made up of Carbon, Hydrogen and Chlorine.
- Hard PVC - Window frames, water pipes.
- Soft PVC - Wire insulation, Clothing.
- PVC film - Hospital blood bags and drip bags.
- PVC is softened using Plasticisers. They are very small and can escape from the plastic and dissolve in liquids in contact with it.
- Plasticisers are linked to Cancer and Infertility.
- In the EU some plasticisers have been banned from children's toys.
- The PVC makers say they do not harm anyone.
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