The Structure of the Earth
It is difficult to study the structure of the Earth because:
- the crust is too thick to drill all the way through
- scientists need to study seismic waves made by earthquakes or man-made explosions.
The lithosphere consists of the crust and outer part of the mantle. It is the relatively cold outer part of the Earth’s structure. The lithosphere is broken into large pieces called tectonic plates. These are less dense than the mantle underneath.
Magma rises up through the Earth's crust because it's less dense than the crust. This can cause volcanoes.
Igneous rock is formed from lava.
Rock hardness: limestone= sedimentary rock made from soft sediments compressed and cemeted together.
marble= metamorphic rock formed when limestone is changed by eat and pressure, typically composed of interlocking mosaic of carbonate crystals. Is harder than limestone
Granite= igneous rock which forms when magma cools and solidifies and has interlocking crystals making it very hard.
Thermal decomposition: reaction where one substance breaks down due to heat to give at least 2 new substances.
Cement is made when limestone is heated with clay.
Concrete is made by mixing cement, sand and small stones with water.
Reinforced concrete is a composite material.A steel support is made by joining steel bars or cables together and this is then usually surrounded by a mould. Concrete is poured into the mould, where it fills the gaps in the steel support and sets hard.
Impure copper can be purfied using an electrolysis cell.
Advantages: The recycling of copper is cheaper (because it has a low melting point), and uses less energy and resources than extracting fresh copper from its ores.
Disadvantages: the separating process may cause pollution, less copper mined so less jobs, small amounts of copper used in electrical equipment is difficult to separate.
Impure copper is purified by electrolysis in which the anode is impure copper, the cathode is pure copper and the electrolyte is copper sulphate solution.
+ anode loses mass as copper dissolves.
-cathode gains mass as pure copper is plated onto it.
mixture of two elements, one of which is a metal. Alloys often have properties that are different to the metals they contain. This makes them more useful than the pure metals alone.
Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms. This makes it more difficult for the layers to slide over each other, so alloys are harder than the pure metal they contain.
Some smart alloys return to their original shape after being heated to a certain temperature.
amalgam mercury dental fillings brass copper and zinc musical instruments, coins, door knockers solder lead and tin joining electrical wires and components
Rusting is an oxidation reaction.
iron + water + oxygen → hydrated iron(III) oxide
Unlike iron and steel, aluminium does not rust or corrode in moist conditions. Its surface is protected by a natural layer of aluminium oxide.
Most iron is converted into steel (an alloy) before being used. Compared to iron, steel is:
- harder and stronger
- less likely to rust.
European Union law requires that at least 85 per cent of a car’s materials can be recycled, rising to 95 per cent by 2015. Recycling reduces the amount of waste, and the use of natural resources.
Manufacturing Chemicals (Making Ammonia)
The Haber Process- Raw materials for this process are nitrogen and hydrogen:
- hydrogen is obtained by reacting natural gas with steam, or from cracking oil fractions
- nitrogen is obtained from the air.
nitrogen + hydrogen ammonia (the equation is reversable)
In the Haber process, nitrogen and hydrogen react together under these conditions:
- a high temperature - about 450ºC
- a high pressure
- an iron catalyst.
Making Ammonia (2)
Factors that increase cost include:
- high pressures (they increase the cost of the equipment)
- high temperatures (they increase the energy costs).
Factors that decrease
- catalysts (they increase the rate of reaction)
- recycling unreacted starting materials
- automating equipment (because fewer people need to be employed, cutting the wage bill).
Acids and Bases
Bases are substances that can react with acids and neutralise them. Alkalis are bases that are soluble in water.
In all solution, all acids contain hydrogen ions, H+. The greater the concentration of these hydrogen ions, the lower the pH.
The name of the salt produced in a neutralisation reaction can be predicted
hydrochloric acid+copper oxide→copper chloride + water
sulfuric acid+sodium hydroxide→sodium sulfate + water
nitric acid+calcium hydroxide→calcium nitrate + water
phosphoric acid+iron(III) oxide→iron(III) phosphate + water
Fertilisers and Crop Yields
Fertilisers make crops grow faster and bigger so that crop yields are increased. They are water-soluble minerals. They must be able to dissolve in water so that plants can absorb them through their roots.
The world population is increasing all the time, so more food has to be produced.
However, if too much fertiliser is used it can pollute water supplies. It may also lead to eutrophication.
The preparation of a fertiliser in a lab involves the following equipment:
- a measuring cylinder to measure a particular volume of an alkali solution
- a burette to add acid a little at a time until the alkali has been neutralised
- a filter funnel to remove solid crystals of fertiliser after evaporating some of the water from the neutral fertiliser solution.
Chemistry of Sodium Chloride
Common salt is sodium chloride, NaCl. Can be made in a laboratory but is found naturally in large amounts in sea water or in underground deposits. It is often obtained either by evaporating sea water or by mining underground deposits.
Salt can be mined as rock salt which is used to treat icy roads in the winter. It lowers the melting point of the ice on the roads so that it melts, even when the temperature is below 0ºC.
Sodium chloride is the raw material for the manufacture of hydrogen, chlorine and sodium hydroxide by electrolysis.
- chlorine gas forms at the anode (positive electrode)
- hydrogen gas forms at the cathode (negative electrode)
- a solution of sodium hydroxide forms.