The Earth's Surface is Made Up of Tectonic Plates
The crust and the upper part of the mantle are cracked into a number of large pieces called tetonic plates, which move around, a few cm per year relative to eachother.
This means that different parts of the world have been located at different positions.
Magnetic Clues in Rocks Show the Movement of Tectonic Plates
When tectonic plates move away from eachother, under the sea, magma from the mantle rises up and solidifies forming new crust. When it is formed, it's magnetised by the Earth's magnetic field, which every half million years or so, swaps direction. This means the rock either have normal or reversed polarity so we can estimate the age of the parts of crust, and track the movement of them.
Sedimentary Rocks Contain Clues to the Earth's History
Geologists can look at different features of rocks to learn about the environment in which they were formed in. Fossils can tell you the age of the rock, and th econditions under which it was formed. Rock formed underwater often contains shells and has ripples created by the sea or rivers. The shape of grains in sedimentary rocks can tell you if the rock was formed underwater or on the surface.
Minerals in the Earth's Crust
The Earth's Crust contains Different Minerals
These minerals are formed by a range of different processes, such as sedimentation, dissolving, evaporation, erosion and mountain building. Chemical industries tend to establish where useful mineral resources can be found. FOr the examble, Limestone, Salt and Coal are all avilable in the NW of England.
Limestone is a Sedimentary Rock Formed from Seashells
Lime stone is grey/white and consists of mainly calcium carbonate. All sedimentary rocks are formed from layers of sediment laid down in lakes or seas, from the shells and bones of sea creatures or the erosion of other rocks. Over millions of years, the layers of sediment get buried under more and more layers. The weight squeezes out the water. Fluids flowing through pores in the sediment deposit natural mineral cement that holds the sediments together.
Coal is also Sedimentary Rock
Coal is formed over millions of years by the fossilisation of layers of plant matter. It consists of mainly the element carbon, and the hard types of coal are formed when coal deposits are put under high pressures and temperatures. This can happpen during the process of mountain building.
Salt is Left Behind by Evaporation
Underground deposits of salt were formed when ancient seas containing dissolved salt evaportated. The salt was left behind and was buried and compressed by other layers of sediments over millions of years. There are massive underground deposits of rock salt under Cheshire and Teeside.
Rock salt is drilled, blasted and dug out fromt he ground, and brought to the surface using machinery. Most rock salt obtained this way is often used as grit. It melts the ice by lowering hte freezing point to around -5, and then provides grip on unmelted ice. It can also be separated out and used in food or for making chemicals.
Water is injected through and outer pipe, which then dissolves the salt, making brine. Pressure forces the brine to the surface where it is stored in wells above the surface and pumped to a refining plant when needed. Here impurities are removed and is pumped into containiers. It is then boiled, to leave the salt for use in table salt and chemical production.
Disadvantages of Salt Mining
- Land above disused mines can collapse into holes (subsidence). However, this risk can be reduced by leaving well supported caverns in mines. Caverns can also be spaced well apart and filled in when no longer used.
- Mining requires lots of energy, mainly generated from burning fossil fuels, producing pollution and using up finite resources.
- Moreover, it can disturb local wildlife.
Salt Can Also be Obtained from the Sea
Seawater flows into shallow pools and is left of evaporated in the sun, leaving the salt behind. This is repeated several times, and the salt is then collected. This can be nearly 100% sodium chloride. However, this method can only be used in hot, coastal areas, where it rarely rains. This land is often used and very expensive to buy.
Salt in the Food Industry
Salt is Important in Food Production
Refined salt is added to most processed foods to enhance the flavour. It's also used as a preservative, giving them a longer life, and therefore a longer shelf life. When salt is added to meant, it absorbs the water and bacterial cells, preserving the meat.
There are also Health Issues regarding Salt
Eating too much can cause high block pressure, potentially leading to Stroke and Heart Disease. It may also increase chances of stomach cancer, osteoporosis and renal failure. We eat a lot of salt without realising it.
Government Guideline for Salt Intake
Independent food safety watchdogs have provided advice about food safety and heath (Food Standards Agency). They have issued GDAs depending on age. The Department of Heath and the Department for Environment, Food and Rural Affairs are also involved in food safety issues. They carry out risk assessments for chemicals in food and advise the public about how food affects their health. Food manufacturers may still include salt in their products as if the recipe is changed, the product may not taste as good or last as long, and the cost of reformulating recipes may be too great. This may lead to the decline of sales.
Electrolysis of Brine
Salt is and Important Source of Chemicals
In order to create chemicals, they electrolyse the brine, by passing and electric current through it. This causes chemical change, splitting the solution into hydrogen, chlorine and sodium hydroxide.
- Chlorine is then used in disinfectants, killing bacteria, household bleach, plasticsl, hydrochloric acid and insecticides.
- Hydrogen is used to make ammonia, used to change oils into fats, and is used in a fuel for fuel cells, and for welding and metal cutting.
- Sodium Hydroxide is a strong alkali and is used int he manufacture fo soap, ceramics, rganic chemicals, paper pulp, overn cleaner and household bleach. Bleach is made by reacting chlorine with sodium hydroxide.
Large Scale Electrolysic Impacts the Environment
It requires a lot of energy, as well as producing mercury. This is a toxic chemical and contamination can cause fisheries to close, and can make people seriously ill. Asbestos is often used in industrial electrolysis. This is another toxic chemical and can cause lung cancer.
Chlorine is Used in Water Treatment
In the UK, drinking water is treated to make it safe. It kills disease causing micro-organisms, and can even kill bacteria that may enter the supply after treatment. It also prevent sthe growth of algae, removes bad tastes and smells, and removes discolouration.
In 1995, the WHO and UN estimated that a billion people don't have access to clean drinking water. It's very expensive to get clean water in many developing countries, in isolated rural areas, many people have to walk miles to get water. The biggest increases in life expentency are linked with the ability to provide clean water. In November 2004, the WHO said that improving drinkin water quality could reduce diarrhoeal disease by up to 40%.
Chlorine Can be Made from Hydrogen Chloride.
The properties of compound are different from the properties of the elements from which they are made. For this ready, it has to be separated. Cholorine can by made my electrolysis or by oxidation of hydrogen chloride.
Chlorination can have Disadvantages
Water contains organic coupounds which react to form chlorinated hydrocarbons. Many of these are carcinogenic. Chlorine gas is also harmful, and liquid cholorine causes chemical burns.
An Alkali is a Compound that Forms Hydroxide Ions when Dissolved in Water
This includes soluble hydroxides and carbonates: Sodium Hydroxide (NaOH), Potassium Hydroxide (KOH) and Calcium Carbonate (CaCO ).An acid and alkali react together to form a slat and water. The products of the neutralisation reaction aren't acidic or alkaline.
ACID + HYDROXIDE SALT + WATER
ACID + CARBONATED SALT + WATER + CARBON DIOXIDE
They type of salt depends on the type of acid and alkali.
NaOH + HCl NaCl + H O
CaCO + H SO CaSO +H O + CO
Alkalis have been Used for Hundreds of Years
Crops need neutral soil to grow, so acidic soil is neutralised by alkalies. Natural dyes are made from alkalis. They are also used to convert fats and oils into soap. The manufacturing of glass often uses alkalies.
Before industrialisation, people relied on burnt wood and stale urine for alkalis. Increaed use of alkalis in industry lead to a shortage.
The LeBlanc process was a process invented to make alkali sodium carbonate on a large scale. Sodium chloride was mixed with sulfuric acid before being heated with charcoal and limestone.
The process itself was very polluting. It released huge volumes of an acid gas (hydrogen chloride) into the air that wrecked the surrounding land. It also produced large amounts of solid waste that slowly released the toxic gas hydrogen sulfide. This gas has a characteristic smell of rotten eggs.
Impacts of Chemical Production
Lots of Products Can be Made Using Chemistry
A large number of chemicals are used in industry to make a wide range of products. For instance, drugs, fuels and plastics. There are so many chemicals, they can't all be tested as thoroughly as we'd like. This means there is not enough data to tell whether some chemicals are a risk to the environment or public health.
Some Chemicals Stay in the Environment for a Long Time
Toxic chemicals will stay in the environment if they're not broken down. Chemicals that end up in waterways or are eaten by animals may be carried over long distances and so spread over a large area as it moves from place to place. They may also be passed along the food chain and cause harm to other animals and humans.
Plasticisers can Harm the Environment.
PVC is a very common polymer that contains carbon, hydrogen and chlorine. Plasticisers called PCB have been used to make PVC more heat and fire resistant, as well as flexible. The PCBs can leach out of the plastic, and they are toxic. PCBs were used in things like medical equipment, used for drips and storing blood. This may have dissolved into the liquids.
Life Cycle Assessments
A LCA looks at every stage of a product's life to assess the impact it would have on the environment.
Material Choices: Most chemical manufacture needs water. Metals must be mined and extracted from ores. This needs a lot of energy. Raw materials often come from crude oil, which is non renewable. Refining crude oil is also polluting.
Manufacture: Manufacturing products uses a lot of energy and other resources. It can cause a lot of pollution and disposal of waste products must be considered. Some waste could be recycled and used for other things.
Use: Using the product could also damage the environment. For instance paint gives off toxic fumes, and furtilisers could leach into streams, causing damage to ecosystems.
Disposal: Many products are disposed of in a landfill site using up space and pollutes land and water. They might also be incinerated, causing air pollution.
Some products may be recycled, processing the materials to be used in new products.