C3: Chemicals in Our Lives: Risks and Benefits

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  • Created on: 06-03-16 17:12

Origins of Mineral Wealth in UK

  • Geologists are scientists who study rocks and the processes that formed them. They try to explain the past history of the surface of the Earth by modelling processes that can be observed today. 
  • We know that the Earth's lithosphere (the crust and the upper part of the mantle) is 'cracked' into several large pieces, called tectonic plates.
  • Intense heat, released by radioactive decay deep in the Earth, causes molten rock to rise to the surface at the boundary of the plates causing the tectonic plates to move very slowly.
  • Geologists use magnetic clues in rocks to track this very slow movement of the plates. They have shown that parts of ancient continents have moved over the surface of the Earth to make up Britain as we know it today. As a result, rocks found in different parts of Britain were formed in different climates.
  • Over millions of years, a number of processes have led to the formation of valuable resources in Britain, such as coal, limestone and salt: mountain formation, erosion, sedimentation, dissolving, evaporation.
  • Igneous rocks are formed from molten magma and contain interlocking crystals. Granite/basalt.
  • Metamorphic rocks are usually formed from sedimentary rocks subjected to intense heat and pressure. Slate/marble.
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Tectonic Plate Movement

  • Earthquakes occur at the boundaries of tectonic plates and mountains are formed when collisions occur between tectonic plates.
  • Plates Slide Past Each Other - When plates slide past each other, huge stresses and strains build up in the crust. These stresses and strains need to be released in order for movement to occur. This 'release' of energy results in an earthquake.
  • Plates Move Away from Each Other - When plates move away from each other, fractures in the crust occur at the boundary. Molten rock rises to the surface, where it solidifies. Mid-ocean mountain ridges are often formed under the ocean this way. Islands are made when the new rock builds up above the level of the sea. E.g. Iceland is part of the Mid-Atlantic Ridge.
  • Plates Move Towards Each Other - When plates collide, the huge pressures cause the rocks to fold and buckle, resulting in the formation of mountain chains. Sometimes as the plates collide, one is forced under the other and new mountains are made along the plate boundary.
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Moving Rocks

  • As newly formed mountains are exposed to the climate, they are weathered by biological, chemical and physical processes, as shown in the rock cycle. As a result, small fragments of rock are broken off. The fragments are transported, often through rivers, to different places by the process of erosion.
  • During erosion the fragments are broken down further, into smaller pieces or sediments, as they bump into things. Minerals in the rock, such as salts, dissolve and are carried by the river to different places. Eventually, the river deposits the small sediments on the riverbed or as they enter a lake or the sea. During warm weather water from enclosed lakes evaporates, leaving beds of sedimentary evaporate minerals including salt crystals.
  • Organic waste such as leaves, or the skeletons of marine animals, will also be deposited on the river or sea bed. Over millions of years, the layers build up and sedimentation occurs. These processes result in the formation of sedimentary rocks such as rock salt,limestone&coal.
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Looking at the Evidence

  • Today geologists study sedimentary rocks to try to understand how they were formed and where the rocks came from. They look for clues buried in the rocks including fossils, the presence of shell fragments, ripples from sea or riverbeds and the shapes of water-borne grains compaired to airborne grains.
  • The chemical industry developed in the north-west of England because resources such as salt, limestone and coal were available locally. This meant that raw materials could be mined and used in one place, rather than having to be transported to a different part of the country. This made economic sense and provided a good range of jobs for local people.
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Salt Mining

  • Salt can be obtained from the sea or from underground salt deposits. Two different processes are used for extracting the salt from underground deposits. The method used may be determined by how the salt is going to be used.
  • Method 1:Mining - Explosives are used to blast the exposed layer of rock salt. The rock salt is loaded into a crusher, where it is ground up into small pieces. A conveyor belt transports the salt to the lift shaft. It is transferred into hoppers and taken to the surface. The salt is then put into large storage areas awaiting collection.
  • The main use of this rock salt is to treat roads during icy conditions. It is taken by lorry to local authorities throughout the UK. Under the Chesire countryside, there are more than 120 miles of empty mine tunnels. The salt mines have also left scars on the landscape, especially where large areas of the ground have been dug out.
  • Method 2: Solution in Water - Salt is soluble in water. Important industrial chemicals such as chlorine and sodium hydroxide are extracted by the electrolysis of brine. Salt can be extracted from the ground in a solution and piped directly to the electrolysis plant.
  • Process - Holes are drilled into salt deposits. Explosive or hydraulics may be used to make the holes larger and so make it easier for the water to penetrate the rock salt. Water is pumped into the bores and the salt dissolves. The salt solution is then pumped back to the surface and piped to the processing plant.
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Uses of Salt

  • Salt (sodium chloride) is a very useful chemical. Some of its uses are flavouring, a preservative in foods, a source in chemicals for things such as bleach and treating the roads.
  • Salt is added to food for flavouring as a preservative. Sodium is present in additives such as sodium bicarbonate. Processed foods, such as meat and bread products, can be high in salt. Processed foods are thought to account for about 75% of the average person's salt intake.
  • Salt is an important component of a healthy diet. It is needed to maintain the concentration of body fluids. It helps cells to take up nutrients and plays a crucial role in the transmission of electrical impulses in the nerves.
  • However, too much salt is not good for you.When the levels of sodium are too high,it causes water to be retained in the body,which means the volume of fluid increases.Some scientists think that this results in high blood pressure,which can increase the risk of heart attacks/strokes
  • Government guidelines recommend that adults should eat 6g of salt each day. However, the average intake of salt is between 9g and 10g a day.
  • Experts estimate that if average consumption was cut to 6g a day, it would prevent 70000 heart attacks and strokes a year.
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Food and the Government

  • Government departments, such as the Department of Health and the Department for Environment, Food and Rural Affairs, have a role in making sure that our food is safe, healthy and fairly marketed. They also make sure that food producers are acting within the law. The government departments promote healthy eating and aim to minimise illnesses such as food poisoning. They make sure that food labels are clear and that they say exactly what is in the food.
  • The food labels help people to decide whether or not to buy the product. For example, coeliacs look for labels that say 'gluten free' and vegetarians look to see if the food contains any animal products (some foods state 'suitable for vegetarians').
  • It is important to give the public the most up-to-date information about food safety. In fact, the Food Standards Agency (FSA), an independant government department, was set up to protect public health and consumer interests in relation to food. Government scientists carry out research into food issues such as genetically modified (GM) foods.
  • Sometimes the research findings are controversial and the results are uncertain. Scientists may even disagree about what the results actually mean. Further problems may be encountered from manufacturers who may not want to accept the research findings, as it may not be in their economic interest.
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Food and the Government.

  • If there is any doubt about food safety, then one of the scientific advisory committees is asked to carry out a risk assessment. It must decide if the food contains any chemicals that could cause harm, how harmful the chemicals are, how much of the food must be eaten before it is likely to harm people and if any groups of people are particularly vulnerable, e.g. the elderly, children, or those suffering from illness.
  • The outcome of a risk assessment is often based on experience gained from people or animals eating the food.
  • Sometimes the scientific evidence is uncertain and the risk is unknown, in which case the precautionary principle is applied. Both experts and the public are consulted before the regulators make a decision about food safety.
  • Regulators have to weigh up the costs and benefits of any decision, as the priority is to protect public safety and not just let the new foods be mass produced and put on the market.
  • For example, many people ask questions such as 'Are GM foods safe to eat?'.
  • For many GM foods, scientists simply do not know enough about the science of altering genes, which may lead to health problems in the future. There is also not much data yet on the potential risks to humans and this is why the precautionary principle is sometimes applied.
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The Alkali Industry

  • Long before industrialisation, alkalis were used in everyday life. Alkalis are very important chemicals as they neutralise acids to make salts. Traditional sources of alkali included burnt wood and stale urine.
  • Here are some of the uses of alkalis: neutralising acidic soil, producing chemicals that bind natural dyes to cloth, producing soap and producing glass.
  • Alkali compounds are soluble hydroxides and carbonates. They always react with acids in a similar way:   Acid + Hydroxide ---------// Salt + Water
  • Acid + Carbonate ---------// Salt + Water + Carbon dioxide
  • With increased industrialisation, and more demand for alkaline-based products, there was a shortage of alkali in the 19th century. As a result, people looked for other ways of processing alkali.
  • Early processes for manufacturing alkali from salt and limestone caused a lot of pollution. Large volumes of the acidic gas hydrogen chloride were released into the atmosphere and great heaps of waste that slowly released the toxic and foul-smelling gas, hydrogen sulfide, were also formed.
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The Alkali Industry.

  • Industrialists have a responsibility to try to minimise the pollution caused by chemical processes. Sometimes the problems can be solved by converting the waste pollutant into a useful chemical. For example, in this case, by dissolving hydrogen chloride gas in water you can make hydrochloric acid:
  • Hydrogen chloride + Water -----------// Hydrochloric acid.
  • Alternatively, the hydrogen chloride gas could be used to make chlorine gas by oxidising it:
  • Hydrogen chloride ----------// Chlorine + Hydrogen.
  • The properties of compounds are different from those of the elements from which they are made. For example, in the reaction above hydrogen chloride is a colourless, acidic gas, chlorine is a green gas and hydrogen is a colourless gas.
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Making Chlorine

  • Chlorine is produced by the electrolysis of brine (sodium chloride solution).
  • Passing an electric current through the brine causes a chemical change to take place. This forms new products - chlorine, sodium hydroxide and hydrogen. 
  • Chlorine is used to kill bacteria in drinking water and swimming pools and to manufacture hydrochloric acid, disinfectants, bleach and the plastic PVC.
  • Sodium hydroxide is used in the manufacture of soap, paper and ceramics.
  • Hydrogen is used in the manufacture of ammonia and margarine.
  • The electrolysis of brine can have an impact on the environment. A major concern is the amount of energy required to carry out electrolysis. A cheap supply of renewable energy is needed.
  • Chlorine is added to domestic water supplies to kill any harmful microorganisms that might be present.
  • Chlorinated drinking water protects against illnesses including typhoid fever, dysentery, cholera and gastroenteritis.
  • However, chlorinated drinking water will not kill viruses or parasites.
  • Chlorine was first introduced into drinking water in England in the 1890s and in the USA in 1908.
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Water Purification Using Chlorine

  • Following the introduction of chlorination, there was a decline in the death rate due to typhoid fever in the USA. As more cities across the USA adopted the practice, further reductions were seen until the illness was eliminated in the mid-1940s.
  • The purification of drinking water by filtration abd chlorination is one of the most significant advancements in public health in recent times.
  • Following natural disasters such as flooding, earthquakes or tsunamis, a lack of clean water becomes the biggest threat to the survivors. This is because people are forced to drink untreated water, which still contains bacteria from deadly diseases.
  • However, it is possible that there could be other health problems associated with chlorinated water. For example, if there are traces of some organic chemicals in the water (from large and small industrial enterprises, agriculture, transport, etc.), they could combine with chlorine to make chemicals that are harmful to humans.
  • Research scientists are continuously investigating these possibilities and offering their advice. From time to time there will be some problems with water quality, such as the scare in North Wales.
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Safe and Sustainable Chemicals

  • Today the pace of scientific and technological development is very fast. New chemicals and materials are being produced continuously. Many materials have useful consumer applications (e.g. in nanotechnology), or they are used in the food industry (e.g. genetically modified foods) or pharmaceutical industry (e.g. for the production of new medicines).
  • For many products, scientists have not yet been able to collect enough data to judge whether they are likely to present a risk to the environment and/or human health. Therefore, government departments or individual professionals (e.g. doctors) must decide if the potential benefits outweigh the potential risks. Given below are examples where potential risks unknown:
  • Thalidomide In the 1950s, a drug called thalidomide was prescribed to pregnant women to relieve the symptoms of morning sickness. It had been tested on animals and was considered safe to use. Thousands of babies were subsequently born across the world with serious limb defects and a common factor was found - all the mothers had taken thalidomide in early pregnancy. The drug was withdrawn in 1961. During the initial investigations the drug was never tested on pregnant animals.
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Safe and Sustainable Chemicals.

  • Chlorofluorocarbons (CFCs) In the 1970s, a link was made between CFCs and the destruction of the ozone layer. CFCs had been used in refrigerants and aerosol sprays. Scientists had thought that CFCs were very unreactive molecules, posing no environmental risks. However, it was discovered that once CFCs are released into the environment, they are carried very large distances into the upper atmosphere where they react with ozone and destroy it. Potentially, the molecules could be in the environment for 300 years before they react with the ozone.
  • Polyvinyl Chloride (PVC) PVC is a polymer that contains carbon, hydrogen and chlorine atoms. Plasticisers can be added to the PVC to make it softer and more flexible, so that the range of uses can be expanded. Scientists have now found that the plasticisers can be leached from the plastic into the surroundings, where they may have harmful effects.
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Life Cycle Assessment (LCA)

  • Each part of the life cycle of a product is carefully considered and assessed on the amount of energy and materials (including water) that will be used and how materials will be obtained and disposed if. The outcome of the LCA is dependant on the use of the end product etc.
  • LCAs were introduced in the 1960s to encourage companies to reduce waste and be aware of environmental impact. New laws were put in place to protect the environment; cash incentives were offered to encourage recycling; and in 1996 a tax was introduced to discourage the use of landfill sites.
  • The purpose of an LCA is to ensure the most sustainable method is used, which means meeting the needs of today;s society, whilst allowing for the needs of future generations.
  • Making the material from natural raw materials: Natural raw materials, water and energy needed to make the starting material. Environmental impact from obtaining the natural raw materials. Manufacture: Resources (including water) and energy needed to make the product. EI of making the product from the material. Use: Energy needed to use the product. Energy and chemicals (including water) needed to maintain the product. EI of using the product. Disposal: Energy needed to dispose of the product. EI of landfill, incineration and recycling.
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Materials and Their Functions

  • Different materials can often be used to perform the same job. For example, disposable nappies are made from cellulose fibres, a super-absorbent polymer and fluff pulp, whilst re-usable nappies are made from cloth. Disposable nappies may be more convenient but in a life cycle assessment which one is better for the environment?
  • Since 2003 it has been government policy to encourage parents to reduce the number of disposable nappies they use.
  • The same material can be used to perform different jobs. For example, Teflon (polytetrafluoroethene) which was accidentally discovered by Roy Plunkett, can be used in gaskets and valves, insulation, non-stick saucepans and dentures.
  • Teflon is chemically inert and temperature resistant and there is also little impact on the environment when it is disposed of in landfill sites.
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