- float on crust and upper mantle
- move around a few cm per year, relative to eachother
- move away= exposed mantle= lava comes through, solidifies and forms new seafloor, SEAFLOOR SPREADING. Rocks are polarised by Earth's magnetic field
- magnetic field swaps diretion every 1/2 a million years so rocks either have normal or reversed polarity- pattern can be used to estimate age and track the slow movement of TT
- rocks we find may have been formed in different positions on Earth and therefore different climates, geologists use features of ricks to learn about the environment in which they were formed
- FOSSILS- remaining/ imprints of dead organisms- tell age and conditions it was formed under
- underwater usually means ripples of contain shells
- sediment that made the rock will either have been carried by water or air- look at shapes of grains found (underwater= water bourne)
Minerals in the Earth's crust
- M. formed by a range of different processes, chemical industried tend to build up close to where mineral resources are near (N-W England, limestone, salt, coal)
- Limestone= sedimentary rock, mainly calcium carbonate, whitey-grey, formed from seashells
- Sedimentary rocks= formed from layers of sediment laid down in lakes/seas. Sediment comes from either shells or bones of sea creatures or erosion of pre-existing rocks.
- Erosion- natural weathering of large pieces of rock by rain and wind, creates tiny particles of sediment that build up at the bottom of the sea/lake where they are compressed/ buried. Weight squeezes out the water, , fluids flowing through pored supply a natural mineral cement, hold it down to form rock.
Coal= type of S.R, black, fossiliation of layers of plant matter, mainly carbon, some are v. hard- formed when coal deposits are put under high pressure and temperature (mountain building)
Britain have underground salt deposits where salt is left from ancient seas after evaporation, salt left behind and compressed by other sediment so massive deposits.
- Found in underground depositis w. impurities, can be extracted by natural or solution mining.
- Normal salt mining involves physical extraction of rock salt
- Rock salt is drilled, blasted, dug out and brought to surface using machinery.
- Most rock salt through this is used for grit on roads, could also be seperated and used to enhance food flavour/ make chemicals
- Solution mining: water injected into salt deposits through outer pipe, this dissolves salt to make brine, pressure forces brine up to the surface through the inner pipe, brine is then strored in wells and pumped to a refining plant when needed. Impurities are removed in refining plant and pumped into containers, brine is boiled to make water evaporate, leaving salt behind, most table salt and chemical salt is produced this way.
- Both types impact environment- mainly by subsidence, affects nearby buildings, reduced risk by strong caverns, can be filled in when no longer used, mining needs lots of energy, burning fossil fuels.
- Obtained from the sea, evaporating sea water, built shallow pools left to evaporate, repeated then salt is collect, method produces purest salt.
Salt in food industry
- Refined salt- processed food to enhance flavour, preservative e.g added to meat- absorbs water and bacteria cells- cured meat
- Health issues= can cause high blood pressure- strokes and heart attacks, could cause stomach cancer, osteoporosis, renal failure. Lots in processed foods.
- There are governmental guidelines, watchdogs and FSA advice government
- Department of health and department of food have functions to: carry out risk assessments and advise the public
- Manufacturers still use salt because it would cost too much to reformulate the recipe, could decrease sales bc the product does not last as long and the sales won't be as good.
Electrolysis of salt solution
Salt- important source of chemicals, first thing to do is electrolyse brine, involves an electric current, it causes chemical change, splits solution into hydrogen, chlorine and sodium hydroxide.
Produces lots of useful products
- Chlorine used in disinfectants, killing bacteria, household bleach, plastics, hydrochloric acid, insecticides
- Hydrogen used to make ammonia, to change oils into fats for making margarine, used as a fuel in fuel cells
- Sodium hydroxide - v. strong alkali, used widely in chemical industry: soap, ceramics, organic chemicals, oven cleaner, household bleach.
- BLEACH= made by reacting chlorine with sodium hydroxide
Large scale electrolysis has environmental impacts- needs a lot of energy=fossil fuels. Mercury is a toxic chemical used in many brine electrolysis plants, waste could contaminate water supplies- could harm animals and humans. Asbestos-used in industrial electrolysis, a toxic chemical- can cause lung cancer.
Used to treat water- kills disease causing microorganisms, correct amount added means a but remains in water in water after treatment to kill bacteria further down the pipes, prevents algae growth, bad taste and removes discolouration caused by organic compounds
LEDCs lack access to clean water, it's the biggest increase in life expectancy in most countires' histories.
Chlorine can be made from hydrogen chloride found in salt (sodium chloride) and hydrogen chloride(HCl) but it has to be seperated out before it is used to treat drinking water, as properties of compounds with chlorine in are different from the properties of chlorine alone. So compounds with chlorine may not kill M.Os, adding NaCl to water will just give salty water, Chlorine can be made by electrolysing brine or oxdiation of hydrogen chloride (4HCl =O2 -> 2Cl2 + 2H2O)
Disadvantages: chlorine reacts with organic compounds in water to form chlorinated hydrocarbons, these are carcinogenic, but the benefit outweighs the risk. Chlorine can be v. harmful if breathed in- irritates respiratory system. Liquid chlorine on the skin/eyes causes severe chemical burns- could be fatal.
A COMPOUND THAT FORMS HYDROXIDE IONS (OH-) WHEN DISSOLVED IN WATER
- alkalines include soluble hydroxides and carbonates
- an acid and alkali react to form salt and water, neutral products-neuralisation reaction.
- ACID + HYDROXIDE -> SALT + WATER
- ACID + CARBONATE -> SALT + WATER + CARBON DIOXIDE
- Sodium hydroxide = hydrochloric acid -> sodium chloride + water (NaOH + HCl -> NaCl + H2O) // Calcium carbonate + sulfuric acid -> calcium sulfate + water + carbon dioxide (CaCO3 + H2SO4 -> CaSO4 + H2O +CO2)
- Alkalis have been used for years: crops need neutral soil to grow, some soil is acidic, so it needs to be neutralised, alkalis are used to make chemicals that allow natural dyes to bind to cloth, alkalies convert fats and oiils into soap, also used to manufacture glass.
- Before industrialisation, people relied on traditional sources (burnt wood and urine)
- increases use meant manufacturing became necerssary.
- First process used limestone and calcium carbonate and salt, this caused lots of pollution, including physical wate and the acidic gas (hydrogen chloride) was released into env. Hydrogen sulfide was slowly released by solid wate, it's toxic and a foul smelling gas.
Impacts of Chemical Production
lots of products can be made via chemistry e.g: drugs, paints, acids, alkalis, bleach, agricultural, plastics, metals, fuels
Some stay in environment for a long time if not broken down, they end up in waterways/ eaten by animals and carried over long distances and spread over a large area as animals move from place to place, may be passed along food chain.
- chemicals such as pesticides are sprayed onto crops to kill creatures that damage them
- they are usually toxic to creatures that aren't pests, danger of poison passing on through food chain, could even harm humans.
- Plasticisers can harm env. by leaching out of plastics into water sources, PCBs are toxic and in the same way as pesticides in water, it can accumulate in animals like fish and end up being eaten by humans.
Life Cycle Assessments- show total env. costa
LCA- Show toal environmental costs
1) Choice of material- most chemical manufacture needs water. Metal has to be mined and extracted from their ores, these processes need a lot of energy and cause a lot of pollution. Raw materials for chemical manufacture often come from crude oil ( a non-renewable resource, supplies are decreasing) Obtaining crude oul from the ground and refining it into useful raw materials also requires a lot of enrgy and generates pollution.
2) Manufacture- manufacturing uses a lot of energy and other resources, it can also cause a lot of pollution, need to think about any waste products and disposal of them, some waste can be recycled and turned into other useful chemicals, reducing pollution.
3) Using the product- can damage environment. Paint gives off toxic fumes, burning fossil fuels releases greenhouse gases and other harmful substances. Fertlisers can leach into streams and rivers and cause damage to ecosystems
4)Disposal, products are often disposed of in a landfill site, tales up space and pollutes the land, products might be incinerated = air pollution.