C2 - Chemical resources

Transcription

1 C2 - Chemical resources Highfields School Highfields School 1 RED 2013

2 1 Structure of the Earth Core - made of iron 1.1 Earth structure Mantle - between crust and core HT only - mantle is cold and rigid just below crust, at greater depths hot and non-rigid so able to move Crust - thin, rocky layer Lithosphere - includes upper mantle and crust - relatively cold and rigid - made of tectonic plates which are less dense than mantle below 1.2 Wenger s theory In 1914 Wenger suggested that over millions of years the continents have moved - - continental drift theory Based on the way the continents seem to fit together like a jigsaw and the same fossils being found on continents that are now widely separated Wenger s idea not accepted at the time Evidence to support Wenger s idea built up (e.g. sea floor spreading) and now the theory of plate tectonics is accepted 1.3 Tectonic plates The Earth s crust is split into tectonic plates The plates move very slowly (2.5 cm per year) as a result of convection currents in the non-rigid mantle Plates can:- a) move apart b) collide c) slide past each other sideways As plates slide past each other they can stick and then slip, causing earthquakes Plates that go down at subduction zones partially melt - molten rock forms volcanoes Molten rock under the ground is called magma. Molten rock on the Earth s surface is called lava. HT only Thermal energy from Earth s core causes convection currents in mantle - kinetic energy transferred to tectonic plates Oceanic plates more dense than continental plates and plates cooler at ocean margins so sink and pull plates down Highfields School 2 RED 2013

3 1.4 Molten rock and volcanoes Igneous rocks - rocks formed by the cooling of molten rock If molten rock cools quickly, small crystals (e.g. basalt) If molten rock cools slowly, large crystals (e.g. granite) How a volcano erupts depends on how runny the magma is:- a) iron-rich magma (basaltic magma) is runny - fairly safe as spills out of volcano. HT only - forms iron-rich basalt b) silica rich magma is thicker, explodes, so more dangerous HT only - forms silica rich rhyolite Lava from volcanoes forms very fertile soil - so some people risk living near a volcano to take advantage of the fertile soil 1.5 Studying volcanoes and the Earth s structure Scientists study volcanoes to:- a) predict when they will erupt - but although scientists are getting better at forecasting eruptions (as better understanding and measurements), cannot be 100% certain b) find out about the structure of the Earth Scientists find out about the interior of the Earth by studying lava from volcanoes and by studying the behaviour of seismic (earthquake) waves as they travel through the Earth Highfields School 3 RED 2013

4 2 Construction materials 2.1 Construction materials Rocks are used in the construction of buildings and roads:- granite (HT - igneous rock, hard) limestone (HT - sedimentary rock, softer) marble (HT - metamorphic rock, hard) aggregate (crushed rock and gravel) limestone and marble are both made from calcium carbonate aluminium and iron - extracted from their ores bricks - made from clay glass - made from sand 2.2 Environmental problems of getting rocks from the ground Mines and quarries cause problems:- a) landscape destroyed, has to be reconstructed when mining or quarrying finished b) more noise c) more dust d) more traffic 2.3 Thermal decomposition of calcium carbonate Thermal = heat Decomposition = breaking down heat calcium carbonate calcium oxide + carbon dioxide heat CaCO 3 CaO + CO 2 colourless gas also called QUICKLIME 2.4 Cement and concrete Cement - made by heating limestone and clay together Concrete - cement, sand, aggregate and water are mixed, then allowed to set Reinforced concrete - concrete with steel rods. Concrete provides hardness, steel provides flexibility and strength Highfields School 4 RED 2013

5 3 Metals and alloys 3.1 Extraction of copper Copper is found as an ore - copper combined with other chemicals and rock. Copper ore is called malachite Copper is extracted by heating copper ore with carbon The carbon removes oxygen from the copper Reduction is the removal of oxygen from a substance, so the copper ore is reduced (oxidation is the addition of oxygen to a substance) Copper used for wiring and electronics needs to be very pure Copper is purified by electrolysis When an electric current is passed the copper moves from the impure copper electrode to the pure copper electrode The impurities are left behind 3.2 Purifying copper by electrolysis HT only Impure copper as anode (+ve electrode) At anode copper atoms are oxidised (lose electrons) to form Cu 2+ ions Cu 2+ ions attracted to the -ve cathode Pure copper as cathode (-ve ) At cathode Cu 2+ ions are reduced (gain electrons) to copper atoms Highfields School 5 RED 2013

6 3.3 Alloys Alloys - mixture of metals, alloy has different properties to individual metals Examples of alloys:- amalgam - mercury, silver tin and copper (used to fill teeth) brass - copper and zinc (used for musical instruments) bronze - copper and tin (used for musical instruments and statues) solder - lead and zinc (used to join electrical wires) Smart alloys - e.g. nitinol (nickel and titanium), remember shape. Useful for spectacle frames - if bent, return to original shape Topic 1 Structure of the Earth L K J 2 Construction materials L K J 3 Metals and alloys L K J 4 Making cars L K J 5 Making ammonia L K J 6 Acids and bases L K J 7 Making fertiliser L K J 8 Salt (sodium chloride) L K J Highfields School 6 RED 2013

7 4 Making cars 4.1 Iron or aluminium? iron more dense than aluminium iron magnetic, aluminium not iron corrodes (rusts) easily, aluminium doesn t both malleable 4.2 Steel Steel is an alloy of iron and carbon (sometimes with additional elements) Steel harder and stronger than iron Steel less likely to corrode than iron both good electrical conductors 4.3 Materials for cars Car body can be made from steel or aluminium:- aluminium is lighter (HT only - so car more economical) aluminium will corrode less aluminium is more expensive Materials needed to make a car:- steel copper (for wiring) aluminium glass plastics fibres 4.4 Recycling cars From % of a car must be able to be recycled, from 2015 rises to 95% Advantages of recycling:- Less material to dispose of Less energy needed to recycle than to extract from raw materials Limited natural resources (ores and oil for plastics) will last longer 4.5 Rusting of iron Rusting - needs oxygen and water Rusting is oxidation (adding oxygen) Word equation for rusting:- iron + oxygen + water hydrated iron (III) oxide Salt water and acid rain both increase the rate of rusting Aluminium does not corrode as it is protected by a smooth coating of aluminium oxide Disadvantages of recycling Different materials have to be separated Highfields School 7 RED 2013

8 5 Making ammonia 5.1 Ammonia Ammonia (NH 3 ) is used to make fertilisers (allows much more food to be grown) and nitric acid Haber process - makes ammonia from nitrogen (from the air) and hydrogen (from cracking oil or natural gas) Cost of making a new substance like ammonia depends on:- a) Price of energy (gas & electricity) b) Cost of starting materials c) Wages d) Equipment e) How quickly the substance can be made 5.2 Haber process Haber process - makes ammonia:- nitrogen + hydrogen ammonia N 2 + 3H 2 2NH 3 sign shows that this is a reversible reaction - the reaction goes in both directions Conditions used in the Haber process:- 450 C high pressure iron catalyst (to speed up reaction) unreacted nitrogen and hydrogen recycled 5.3 HT only - explaining Haber process conditions Conditions used are:- High pressure - increases percentage yield of ammonia High temperature - decreases percentage yield of ammonia but gives a high rate of reaction 450 C optimum temperature - fast reaction with sufficiently high percentage yield Catalyst - increases rate of reaction but does not change percentage yield 5.4 Cost of making a new substance Cost of making a new substance is controlled by:- Higher pressure = more expensive plant (storage tanks, pipes, reaction vessels, separation equipment) Higher temperature = higher energy cost Catalysts = reduced costs (as reaction faster) Recycling unreacted materials = lower cost Automation = reduces wages bill (does not remove need for workers completely) Daily yield - percentage yield and rate both contribute to daily yield - percentage yield can be low if rate high Highfields School 8 RED 2013

9 6 Acids and bases 6.1 Acids, bases and alkalis Acids - have ph less than 7 Bases - have ph more than 7 Bases are oxides, hydroxides or carbonates of metals Alkalis - are soluble bases (bases that will dissolve in water) Litmus - an indicator that turns red in acid, blue in alkali Universal indicator - gives a range of colours at different ph so can be used to measure ph 6.2 Neutralisation When an acid and a base are added together they react:- acid + base a salt + water Both the salt and water are neutral (ph7) so this is called a neutralisation reaction Carbonates neutralise acids to produce a salt, water and carbon dioxide acid + carbonate salt + water + carbon dioxide Naming salts - a) the first part of the name comes from the first part of the base e.g. Sodium hydroxide gives sodium. Calcium carbonate gives calcium. Some indicators change colour suddenly (litmus) at a particular ph, others change gradually over a range of phs (universal indicator) HT only:- Acids contain H + ions Bases contain OH - ions b) the second part of the name comes from the acid used hydrochloric acid gives a chloride sulfuric acid gives a sulfate nitric acid gives a nitrate phosphoric acid gives a phosphate Example - calcium hydroxide + nitric acid calcium nitrate + water 6.3 Neutralisation - HT only In all neutralisation reactions the H + ions from the acid react with the OH - ions from the alkali to make H 2 O H + + OH - H 2 O Ammonia (NH 3 ) is a base - when it dissolves in water it makes ammonium hydroxide (NH 4 OH) Highfields School 9 RED 2013

10 You need to know all these symbol equations:- 6.3 Neutralisation symbol equations- HT only Not as difficult to remember as it looks - remember the 3 types of reaction and the formulae of the 3 acids and you are half-way there already! Remember that HCl and HNO 3 have one hydrogen ion but H 2 SO 4 has two hydrogen ions Remember that Ca and Cu compounds need two hydrogen ions - so only need one H 2 SO 4 but 2HCl or 2HNO 3 Remember NH 3 only needs one hydrogen ion so if reacting NH 3 with H 2 SO 4, need 2NH 3 Highfields School 10 RED 2013

11 7 Making fertiliser 7.1 Fertilisers Fertilisers increase crop yield by providing plants with essential chemical elements Plants need nitrogen (N), phosphorus (P) and potassium (K) Fertilisers that provide these elements are known as NPK fertilisers Plants can only take up these chemical elements through their roots if the fertiliser is dissolved in water Fertilisers - allow food for a rising world population but excessive use of fertilisers can result in eutrophication and water pollution 7.2 Fertilisers - HT only Fertilisers replace essential elements used by previous crop or provides extra essential elements Nitrogen from fertilisers gets incorporated into plant protein, increases growth Stages of eutrophication:- 1) fertiliser washes off into rive or lake 2) extra nitrate or phosphate causes algal bloom 3) blocks sunlight to other plants which die 4) aerobic bacteria use up all the oxygen decomposing the dead plants, most living organisms die 7.3 Making a fertilisers Add more acid until neutral Highfields School 11 RED 2013

12 8 Salt (sodium chloride) 8.1 Salt Salt can be obtained by:- 8.2 Electrolysis of brine (concentrated sodium chloride solution) a) evaporating sea water b) mining in Cheshire as solid rock salt c) solution mining in Cheshire (water pumped down pipe, salt dissolves, salt water pumped up second pipe) Mining for salt can lead to subsidence - taking salt out leaves a hole underground, rock can collapse into hole, buildings collapse Test for chlorine Chlorine bleaches (removes the colour) damp litmus paper 8.3 Uses of salt and products made from salt Salt used as a preservative and as a flavouring Chlorine is used to sterilise water and to make PVC and solvents When electricity passed through brine:- - hydrogen gas at cathode - chlorine gas at anode - sodium hydroxide left in the water Electrodes (anode and cathode) must be inert so they don t react with hydrogen, chlorine or sodium hydroxide HT only:- Hydrogen is used in the manufacture of margarine Sodium hydroxide is used to make soap Bleach is made by reacting sodium hydroxide and chlorine together Chlor-alkali industry - industry based on the electrolysis of brine - very important, worth billions of pounds a year The table to record your revision progress is on page 6 Reduction at cathode 2H + + 2e - H 2 Oxidation at anode 2Cl - - 2e - Cl 2 Highfields School 12 RED 2013