The structure of the Earth
The lithosphere is a relatively cool layer of the earth's structure, comprised of the crust and top of the mantle. Tectonic plates are less dense than the mantle.
The crust is too thick to drill thorugh and the extreme temperatures and pressure at such depths mean that our data has to be collected using sesmic waves produced by earthquakes and explosions.
Oceanic crust is denser than continental; when these plates collide the oceaninc sinks pulling more down and partially melting when it reaches the hotter part of the mantle. (this magma then rises to create volcanoes) This is Subduction.
Wegener's theory of plate techtonics is now widely accepted as it has a wide range of evidence and it has been discussed and tested by many scientists.
Geologists study volcanoes to try and forecast future eruptions or find info on the structure of the earth.
Iron-rich basalt comes from runny lava in slower volcanic eruptions. Silica-rich rhyolite rock comes from thick lava in explosive eruptions.
Raw materials & Rocks
Clay --> Brick
Limestone + Clay --> cement
Sand --> glass
The hardness of materials can be compared by rubbing them together.
Sedimetary = soft sediement held toghether, stuck together by fossiles + pressure
Metamorphic = heat + pressure. Iterlocking mosaic of carbonate crystals
Igeneous = solidified magma . Interlocking crystals.
Cement, concrete & Reinforced concrete
Themal decomposition is where a susbatance breaks down on heating to give at least two or more different substances.
eg. Calcium Carbonate -> calcium oxide + carbon dioxide
CaCO3 -> CaO + CO2
Cement is made when limestone is heated with clay.
Concrete is made by mixing cement, sand and small stones with water.
Reinforced conrete is a compostite material which has steel rods or meshes running thorugh it.
Reinforcement is needed because concrete is only strong under compresion not tension so when it bends, the underside of concrete crack. The reinforcements keep it rigid and stop it curving or flexing and cracking/breaking.
Advantages: a fairly low melting point means low energy costs; it reduces the need for mining, saving resources and the environment; it keeps the cost down.
Disadvantages: the small amounts used in electrical equipment is hard to separate; less copper is mined meaning less jobs; a lot is thrown away as it is difficult to recycle.
In the purfication of copper by electrosis, an electrolyte of copper(II) sulphate solution.
At the Anode, the Cu lose electrons to form Cu2+ Ions. This called oxidisation.Cu - 2e- -> Cu2+
These Cu2+ ions travel thorugh the electrolyte to the negatively charged cathode and forms pure copper at the cathode Cu2+ + 2e- -> Cu (This is reduction)
Alloys are mixtures containing at least one metal.
Alloys have different properties. Eg.
amalgam, contains mercury (used for filling teeth)
brass = copper + zinc
solder = lead + tin
Some smart alloying return to their original shape after being heated to a certain temperature.
Nititol (nickel-titanium) is a smart alloy; used to make spectacle frames.
Rust & Corrosion
Only Iron and Steel rust. Acid and salt accelerate rusting. Rusting is an oxidation reaction because iron reacts with O2.
Aluminium does not corrode in the moist air as it forms a protective layer of aluminum oxide which unlike rust doesn't flake off.
Different metals corrode at different rates.
Materials used in cars
aluminium in car bodies - doesn't corrode, low density, malleable, quite strong
iron or steel in car bodies - malleable, strong
copper in electrical wires - ductile, good electrical conductor
lead in lead-acid batteries - chemical reaction with lead oxide produces electricity
plastic in dashboards, dials, bumpers - rigid, doesn't corrode, cheap
pvc in metal wire covering - flexible, does not react with water, electical insulator
glass and plastic/glass compostie in windscreens - transparent, shatterproof
fibre in seats - can be woven into textiles, can be dyed, hard-wearing
The alloy: steel is harder and stonger than iron and less likely to corrode than iron.
Aluminiumlighter-better fuel economymore resistant to corrostion-lasts longer
Advantages: less mining; less crude oil needed; less waste in landfills; fewer toxic materials, such as lead batteries is dumped.
Disadvantages: fewer mining jobs; difficult to seperate the materials; some separating techniques produce pollution; some recycling techniques are expensive.
There are laws which specify that a minimum percentage of materials used must be recyclable to help protect the environment.
The Haber process
We need Nitrogen-based fertilisers. These fertilisers are made from ammonia, which is made using the Haber process.
Nitrogen + Hydrogen <=> ammonia
N2 + 3H2 <=> 2NH3
Optimum conditions = catalyst=irontemp=450C_pressure=200atmrecycle-unreacted_N2_H2
This is as efficent as possible because:
-Iron catalyst increases the rate of reaction (rate of succesful collisions) (not percentage yield)
-High pressure increases the percentage yield of ammonia
-A high temperature increases the reaction rate + breaks down ammonia; reducing percentage yield
-Optimum temperature is around 450C. Although the yield is not very high, the rate is fairly quick. This is the best compromise or 'best of a bad balance'.
Cost of Chemical manufacture
Cost=Increased: +pressure_plant-costs +temperature_energy-costs
Cost=decreased: +catalyst +recylced +automation_wage-costs
Economic considerations mean that:
-Both the reaction rate and the percentage yield must be high enough to give a sufficient daily yield of product.
-A low percentage yield can be accepted if the reaction can be repeated many times with recycled starting materials.
-Optimum conditions give the lowest cost, rather than the fastest rate or highest yields.
Acids & Bases & Nutralisation
Metal oxides and metal hyroxides are bases. A few bases are soluable in water, so are called alkalies
Neutralisation = acid + base -> salt + water
Some indicators show a sudden colour change at one pH value. UI (universal indicator) shows a range of different colours.
In solution, all acids contain H+ ions (hyrogen ions). The Higher the concentration of H+ ions the lower the ph and therefore the stronger the acid. Neutralisation leaves no free H+ left.
Alkalis contain OH- Ions (Hyroxide ions)
Neutralisation involves the reaction
H+ + OH- -> H2O
Acid + base -> salt + water
Acid + metal carbonate -> salt + water + carbon dioxide
Sulfiuric acid will become something sulfate
Nitric acid will become something nitrate
Hydrocloric acid will become something chloride
Phosphoric acid will become something phosphate
Hydrochloric acid + copper carbonate -> copper chloride + water + carbon dioxide
HCl + CuCO2 -> CuCl2 + H2O + CO2
Fertilisers & Eutrophication
Fertilisers; because they replace important elements used by previous crops and so they can provide nitrogen that is encorporated into the plant's protein resulting in increased growth.
The feritlisers must be dissolved in liquid as only dissolved substances are small enough to be absorbed by the plant's roots.
Eutriphocation: The nitrates and phosphates contaminate the water sauce, causing an algal bloom and this blocks sunlight to the other oxygen producing plants which die. Anarobic bacteria use up the oxygen on the water and feed on the dead and decaying plants. Fish die.
As many fertilisers are salts, so they made by reacting an acid and alkali to make salt and water. Eg.nitric acid and ammonium solution makes ammonium nitrate.
Fertilisers are made using this process:
-The alkali is titrated with the acid using an indicator to find out how much of each is needed.
-Another batch is made with the found quantaties and then the dissolved fertiliser is heated to evapourate most of the water off, then left for the remaining solution to crystalise. The crystals are then to filtered off.
Salt is mined in cheshire in two different ways: mining it from the ground as rock salt; solution mining by pumping in water and extracting saturated salt solution.
Mining salt can lead to subsitdance. The ground above a mine can sink causing landslips and destroying homes. Salt at the surface, particulary brine solution, can escape and affect habitats.
Sodium Chloride (brine) can be seperated using electrolysis. The anode and cathode are placed in sodium hydroxide. The Na+ and H+ ions migrate to the negative cathode. The Cl- and OH- ions migrate to the positive cathode.
At the cathode (reduction) 2H+ + 2e- -> H2
At the anode (oxidation) 2Cl- - 2e- -> Cl2
The ions not discharged make Na+ + OH- -> NaOH
Sodium hyroxide and chlorine are important raw materials. They are involved in making about half the chemicals we use on a dialy basis including solvents, plastics, piants, soaps, medicines and food additives. Sodium Oxide and chlorine are used to make bleach.