Chemistry C2

Key points in module C2 - Chemical Resources

Exam board ocr gateway - new 2011 course.

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The earths structure.

  • The crust is the Earths thin outer layer and is about 20km deep.
  • The lithosphere includes the crust and upper part of the mantle and is made up of tectonic plates.
  • The mantle is the soild section between the crust and core.
  • The core is over half the earths radius. The inner core is solid but the outer core is liquid.
  • Convection currents caused by heat, which is caused by radioactive decay, is what moves tectonic plates
  • Tectonic plates move about 2.5cm a year.
  • Seismic waves tell us whats below the crust by measuring the time it takes them to travel through the earth and where they are detected.
  • P-waves can travel through liquids and solids.
  • S-waves can only travel through SOLIDS.
  • s-waves travel through the mantle which shows its soild but not through the core so it must be liquid.
  • p-waves travel faster through the inner core suggesting its solid.
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Plate tectonics.

  • Fossils of similar plants and animals had been found on opposite sides of the atlantic ocean. People thought this was because of land bridges.
  • In 1914 Alfred Wegener thought that Africa and South America had been one continent.
  • Evidence matching rock layers on each continent and similar earthworms.
  • Wegeners theory of continental drift said there had been one super continent Pangaea.
  • His theory wasn't accepted at first because it was a big change in ideas. Also the movement wasn't detectable so his theory wasn't convincing enough.
  • In 1960s the idea was fully accepted. Firstly when scientists investigated Mid-Atlantic ridge and  they found magma rising up from the sea bed solidifying and forming underwater mountains. This suggest the sea floor is spreading.
  • Also more evidence is that continents are moving apart from magnetic orientation of the rocks. As liquid magma erupts, iron particles in rocks align themselves with Earths magnetic field. They cool and set this shows new sea floor is being created so coninents are moving apart.
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Volcanic eruptions.

  • Volcanoes occur when magma from the mantle emerges through the Earths crust.
  • The crust at the ocean floor is denser than the crust below continents.
  • When two tectonic plates collide, a dense ceanic plate will be forced under a less dense continental plate - subduction.
  • Oceanic crust tends to be cooler at the egdes of a plate so the edges sink easily.
  • As the oceanic crust is forced down it melts and starts to rise. If this molten rock reaches the surface a volcano forms.
  •  Igneous rock is made when molten rock cools and solidifies. The type depends on cooling time and compostion of magma.
  • Some volcanoes produce iron-rich basalt. The lava from the eruption is runny but the eruption is fairly safe.
  • However if the magma is silica-rich rhyolite, the eruption is explosive.
  • Geologists try to predict volcanoes by looking at magma movement.
  • Living near a volcano has benifits: volcanic ash makes fertile soil.
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Three different types of rock.

  • Sedimentary rocks
  • Formed in layers of sediment laid down in seas or lakes
  • Over millions of years the layers get buried under more layers and the weight pressing down squeezes out the water.
  • Fluids flowing through the pores deposit the natural mineral cement.
  • Limestone is a sedimentary rock fromed from seashells. Its mostly calcium carbonate - when limestone is heated it thermally decomposes to create calcium oxide and carbon dioxide.
  • Metamorphic rocks
  • Metamorphic rocks are caused by heat and pressure on sedimentary rocks.
  • The mineral structure is different but the chemical composition is the same.
  • Marble is a metamorphic rock formed from limestone. Very high temperature and pressures break down the limestone and it reforms as small crystals. 
  • Igneous rocks 
  • Formed when magma cools (see previous card).
  • They contain different minerals in randomly arranged interlocking crystals - this makes them very hard. Granite is an igneous rock.
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Construction materials.

  • Rocks are a mixture of minerals. Ores are minerls we can get useful materials from. Aluminium and iron are examples.
  • Glass is made by limestone (calcium carbonate), sand (silicon dioxide), and soda (sodium carbonate) untill it melts. Then when it cools you have glass.
  • Bricks are made from caly a mineral formed by decomposed rock. Its hardened by firing at high temperatures.
  • Limestone and clay are heated to make cement.
  • Cement can be mixed with water and sand to create concrete.
  • Reinforced concrete is a composite material - a composition of concrete and soild steel support. Its a better construction material than ordinary concrete because it combines the hardness of concrete with the flexibiltity and strenght of steel.

Extracting rocks can cause environmental damge: quarrying use up and destroys land/habitats, transporting rock cause noise and pollution, quarrying creates noise and dust and disused sites can be dangerous.

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Extracting pure copper.

  • Electrolysis is used to obtain very pure copper.
  • Electrolysis means splitting up with electricity - passing a current through impure copper splits pure copper from impurities.
  • Copper is imersed in a liquid called the electrolyte which conducts electricity(electrolytes are usually free ions dissolved in water).Copper sulfate solution is the electrolyte.
  • The electrical supply acts like an elctron pump. It pulls elctrons off copper atoms at the anode, causing them to go into the solution as Cu2+ ions. It then offers electrons at the cathode to Cu2+ ions to turn them back into copper atoms. The impurities are dropped at the anode as slude while pure copper atoms bond to the cathode.
  • The cathode is the negative electrode. It starts as a thin piece of pure copper and more pure copper adds to it.
  • The anode is the positive elctrode. It's a lump of impure copper which will dissolve
  • reduction is the gain of elctrons or removal of oxygen - cathode reaction.
  • Oxidation is the loss of elctrons or the addition of oxygen - anode reaction.
  • Recycling copper aves money and resources.
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  • An alloy can be mixture of two or more different metals. They can also be a mixture of a metal and a non metal.
  • Alloys often have properties that differ from the metals they're made from.
  • Steel is an alloy of iron and carbon
  • Steel is harder than iron. Also its stronger if the amount of carbon doesn't get more then 1%
  • Iron on its own will corrode but steel is less likely to.
  • Brass is an alloy of copper and zinc and most of its properties are a mixture of the two.
  • Bronze is an alloy of copper and tin. Its harder and stronger than tin and more resistant to corrosion. It's is used to make springs and motor bearings.
  • Solder is an alloy of lead and tin. Unlike pure materials it doesn't have a definate melting point but gradually soildifies as it cools.
  • An amalgam is an alloy containing mercury. It is used for fillings
  • Some alloys remember their shape, if they are bent or twisted they go back to their original shape.
  • E.g. Nitinol is a family of alloys of nickel and titanium.
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Building cars.

  • Iron corrodes more than aluminium. This happens when its in contact with water and air. The chemical reaction taking place is an oxidation reaction.
  • Iron + oxygen + water ----> hydrated iron oxide.
  • If the water is salty or acidic rusting is sped up. 
  • Aluminium doesn't corrode when its wet because it reacts quickly with oxygen to create a protective layer of aluminum oxide over it. This stops anymore reactions.
  • Aluminium has advantages over steel - lower density (saves fuel, more efficient). It corrodes less. However it is very expensive.
  • Steel is strong and can be hammered and welded - good fro bodywork.
  • Aluminium is strong and has a low density - used fro parts of the engine.
  • Glass is transparent - used fro windscreens.
  • Plastics are light and hardwearing - used for internal covering.
  • Fibres are hardwearing - used to cover seets and floor.
  • Recycling cars is important - now the metal is recycled but other stuff goes to landfill.
  • When chosing a material manufactures must balance safety, environmental impact and cost. 
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Acids and bases and reaction of acids.

  • An acid is a substance with a pH of less then 7.
  • Acids form H+ ions in water. The pH of an acid is determined by the concentration of the H+ ions.
  • A base is a substance with a pH of greater then seven.
  • An alkali is a base that is soluble in water. Alkalis form OH- ions in water.
  • The reaction between acids and bases is called neutralisation.
  • Acid =base ----> salt + water.
  • Or H+ + OH- <---> H2O.
  • Metal oxides and hydroxides are bases.
  • E.g. acid + metal oxide ----> salt + wate.r
  • Acids and carbonates produce carbon dioxide.
  • Acid + carbonate ---> salt + water + carbon dioxide
  • Acids and ammonia prodeuce ammonium salts.
  • Acid + ammonia ----> ammonium salt.
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  • Fertilisers provide plants with essential elements fro growth
  • The three main things in fertilisers are nitrogen, phosphorus and pottasium.
  • If these elements are missing plants die, fertilisers replace these which increases crop yield.
  • The fertiliser must first dissolve in water
  • Ammonia is a base so can be neutralised by acids (see previous card).
  • Ammonium nitrate - made from ammonia and nitric acid.
  • Ammonium sulfate - ammonia and sulfuric acid.
  • Ammonium phosphate - ammonia and phosphoric acid.
  • Potassium nitrate - nitric acid and potassium hydroxide.
  •  The main problem with fertilisers is Eutrozphication.
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Preparing fertilisers.

  • You can make fertillisers using titration...
  • You need amonia and nitric acid to make ammonium nitrate.
  • Set up you apparatus. Add a few drops of methyl orange indicator to the ammonia - it'll turn yellow.
  • Slowly add the nitric acid from a burette into the ammonia untill it goes red.
  • Methyl orange is yellow in alkalis but red in acids so this colour change means that all the ammonia has been neutralised and you've gotammonium nitrate solution.
  • To get ammonium nitrate crystals evaporate the solution untill only a little bit is left. Leave it to crystalise.
  • The crystals are't pure they contain methyl orange. To make them pure you repeat the titration using how much acid it took to neutralise the ammonia and no indicator.
  • Percentage yield is how much product you actually got compared with what you predicted you would get.
  • The mass of product that you end up with is called the yield.
  • The predicted yield of a reaction is the amount of product that you'd get if all the rectant was converted into product.
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The haber process.

  • The Haber process was developed by Fritz Haber. It takes nitrogen and hydrogen and uses them to make ammonia.
  • It's a reversible reaction N2 + 3H2 <---> 2NH3
  • The nitrogen is obtained from the air and the hydrogen from cracking or natural gas.
  • The reaction is reversible so not all the hydrogen will convert to ammonia.
  • The nitrogen and hydrogen thats not used is recycled.
  • Industrial conditions - Pressue: High (200 atmospheres), Temperature: 450*C, Catalyst: Iron. 
  • High pressures favour the forward reaction - increases %yield.
  • High temperature favours the reverse reaction - decreases % yield.
  • The trouble is lower temperatures mean slow reaction rates.
  • 450*C is the optomum temperature - it gives fast reaction rate and a reasonable percentage yield.
  • The Iron catalyst makes the reaction go faster which gets it to the equilibrium proportions.
  • Without the catalyst the temperature would have to be raised further which would reduce the % yield.
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Minimising the cost of production.

  • Production cost depends on five main things...
  • Price of energy.
  • Cost of raw materials - kept to minimum by recycling.
  • Labour costs (wages).
  • Plant costs (equipment).
  • Rate of production.
  • Optimum conditions are those that give the lowest production cost per kg of product.
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Salt - sodium chloride (NaCl).

  • In Britain salt is extracted from underground deposits like in Cheshire.
  • Rock salt is a mixture of salt and impurities.
  • It is mined by pumping hot water underground . The salt dissolves and the salt solution is froced to the surface by the the pressure of the water- this is called solution mining.
  • When the minings finished the holes must be filled in or the land could collapse - this is called subsidence.
  • Concentrated brine (sodium chloride solution) is electrolysed industrially.
  • The electrodes are made up of an inert material - this is so they won't react with the electrolyte or the products of the electrolysis
  • There are three useful products- hydrogen a the cathode , chlorine gas at the anode and soium hydroxide is fromed from ions left in the solution.
  • Half equations...
  • Cathode 2H+ + 2e- ---> H2
  • Anode 2Cl- - 2e- ---> Cl2
  • The products of chlor-alkali process are used for lots of things eg. hydrogen - ammonia and margaine. Chlorine - disinfect water, plastics, solvents, hydrochloric acid. Sodium hydroxide - soap, bleach.
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