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  • Created on: 07-06-15 19:00

Atoms

All substances are made up of atoms, there are about 100 different types of atom found naturally on Earth. All atoms have a nucleus made of protons and neutrons, this is surrounded by electrons that occupy energy levels around the nucleus. Protons have a positive charge, neutrons are neutral and electros have a negative charge.

Elements contain only one type of element

Compounds contain more than one type of atom 

The periodic table is set out so elements in the same group have similar properties, they all have the same number of electrons 

Chemical reactons - atoms join together with chemical bonds to make compounds, metals and non metals bond ionically. The metal atom loses electrons to form and ion, the non-metal takes the electron forming another ion, these are then strongly attracted to each other. A compound formed by non-metls consists of molecules, each atom shares an elctron with another creating a covelant bond .

word or symbol formulas can be used to represent reactions 

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Limestone

Limestone rock is mainly made of calcium carbonate CaCO3, it is quarried from the ground and can be used for building materials. 

Calcium carbonate + heat ----> Calcium Oxide   +   Carbon Dioxide

       CaCo3                    ---->          CaO         +           CO2

Calcium Oxide  +  Water  ---->   Calcium Hydroxide 

       CaO         +    H2O  ----->            Ca(OH)2

Cacium Hydroxide + water (excess) ----> Calcium Hydroxide solution (limewater)

Calcium Hydroxide solution + Carbon Dioxide  ----> Calcium Carbonate  +  Water

            Ca(OH)2               +          CO2        ---->         CaCO3           +   H2O

To make lots of Calcium Oxide, Calcium Carbonate is thermolly decomposed in a rotary lime kiln where it and hot air is put in and calcium oxide, air and carbon dioxide comes out.

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Limestone uses

Limewater reacts with carbon dioxide to form calcium carbonate - used as a test

Carbonates react with acids to form salts, water and carbon dioxide - calcium carbonate used - this  is why Limestone buildings/statues are damaged by acid rain.

Cement is made by heating limestone and clay in a kiln 

Mortar is made by mixing cement and sand with water

Concrete is made by mixing cement, sand, water and aggregate (small rocks/stones)

Neutralise acidic soil and lakes, powerstation chimneys

Issues

Limestone quarrying forms a huge hole in the ground which leaves a crater, this can be filled with water to form a resevoir. Noise pollution, dust, destroys habitats, pollution from lorries.

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Extraction of Metals

Ores contain enough metal to make extraction economically worthwhile. In many cases the ore is a metal oxide, most metals have to be extracted by chemical reactions. whether it is worth extracting a metal depends on how easy it is to do so and how much the metal is worth at the time. Metals are extracted by reduction or electrolysis. Some ores are concentrated first (getting rid of rock materials)

 If a metal is lower than Carbon in the reactivity series it can be extracted using reduction. If you heat a metal oxide with carbon, the carbon removes the oxygen and carbon dioxide is made as well as the metal.

Metals more reactive than carbon have to extracted using electrolysis, The molten compound (electrolyte) is broken down by sending a current through it. It is a very expensive proccess as high temps are needed.

Copper can be extracted by smelting(heated in a furnace) however this produces impre copper so electrolysis is used to purify the copper. The anode is a large lump of impure copper, the cathode is a thin piece of pure copper that attracts the positively charged CU ions from the anode.

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Copper extraction

Copper can be extracted by:

Smelting - heating in a furnace with carbon

Electrolysis - also used to purify

Displacement  - Cheap iron can be used to replace the copper in copper sulfate solution as it is more reactive and copper metal is produced

Bioleaching - Bacteria can be used to seperate copper from copper sulfate as it absorbs the energy from the bond between copper and sulfur producing copper in Leachate that can then be purified

Photomining - Plants are grown in soil that contains copper, the plants absorb the copper oxides which are then harvested and burned in a furnace. Sulfuric acid is added then the copper sulfate is purified.

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Alloys

Iron can be extracted from iron oxide in a blast furnace. Iron straight from the furnace is not that usefull it is around 96% iron and very brittle, it is known as cast iron and used for stoves and man-hole covers. Pure iron is too soft to be usefull. When mixed with other materials an alloy is created.

Steel is the most common alloy of iron, there are many different types, they involve iron, carbon and sometimes other elements. 

  • Low carbon steel (0.1%) - easily shaped - car bodies
  • High carbon steel (1.5%) - very hard, brittle - blades bridges
  • Stainless Steel (chromium + nickel) - corrosion reasistant - cutlery, containers

Aluminium and titanium are corrosion resistant, strong and have low densities. Aluminium is alloyed with materials to make it harder and is used to make aircraft, it is extracted using electrolysis. Titanium has a very high melting point and used in replacement joints, nuclear reactors and jet engines. It can be reduced by carbon but the titanium becomes brittle, instead it is extracted by sodium and magnesium. First though, the oxide has to be converted to a chloride then distilled.

The transition metals are good conductors of heat and electricity and are malluable. Copper is good for electrical wiring and plumbing

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Crude oil

Crude oil is a mixture of lots of different chemical compounds, most of which are hydrocarbons and mainly these are saturated alkanes. Crude oil is not much use on its own first it has to be seperated different substences with similar properties (fractions), this is done by fractional distillation.

 (http://www.science-resources.co.uk/KS3/Chemistry/Chemical_Reactions/Hydrocarbons/fractioning_column.jpg)

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Burning Crude oil

When hydrocarbons burn in air they release lots of enery this is an oxidisation reaction.

All fossil fuels contain some sulfur which when burnt forms sulfur dioxide, this is a contributor to acid rain - kills trees - damages buildings 

When there is not enough oxygen incomplete combustion happens and Carbon monoxide is formed this is poisonous to us 

The High temperature in engines allow the nitrogen and oxygen in the air to react to form nitrogen oxides which are poisonous and cause acid rain

Disel engines burn much bigger molecules and these do not always fully react and tiny particles of carbon called particulates are released which can damage the lungs and cause cancer.- global dimming

Alternate fuels 

  • Ethanol - fermentation of plants - carbon neutral - engines converted, increase food prices
  • Biodiesel - carbon neutral, less SO2  - can't make enough, expensive 
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Cracking Crude oil

Longchain Hydrocarbons can be cracked to produce smaller,more useful molecules. This process involves heating the hydrocarbons to vaporise them. The vapours are either passed over a hot catalyst of Aluminium Oxide or mixed with steam and heated to a very high temperature (400*C - 700*C) so that thermal decomposition reactions then occur. Shorter chain alkanes and Unsaturated alkenes are produced.

Bromine water test 

Unsaturated alkene + Bromine water ----> coulourless

Saturated alkane + Bromine water ----> orange (no change)

Ethanol

Ethen can be hydrated with steam and a catalyst to produce ethanol

Ethanol is produced by the fermentation of sugar with yeast 

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Polymers

Alkenes can be used to make polymers such as poly(ethene) and poly(propene). In these reactions, many small molecules (monomers) join together to form very large molecules (polymers). This is called polymerisation, the double bond opens up and is replaced with a single bond to another molecule. It all depends on the Temperature and pressure this can change the density and the properties of the material. 

Polymers can be used for all sorts of things - Low density polyethene is used for plastic bags and tights - waterproof coatings - dental polymers for fillings - shape memory polymers, memory foam mattresses - hydrogels used for wound dressings

Most polymers are not biodegradable - not broken down by microorganisms - which makes them hard to dispose. New polymers with cornstarch in have been developed to degrade.

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Plant oils

Some fruits, nuts and seeds contain a lot of oil. These oils can be extracted and used for food and fuels. The plant material is crushed then pressed between two metal plates to get the oil out. Some plants are distilled after crushing them (water and oil evaporated then then collected and oil purified)

Vegtable oils provide a lot of energy, they provide important nutrients such as Vitamin E and contain essential fatty acids which the body needs. Vegtable oils have higher boiling points than water so can cook at higher temps, the oil gives the food a different taste, it increases the energy you get from the food. Rapeseed and Soybean oil can be turned into fuels and biodiesels.

Oils and fats contain chains of hydrocarbons which are either unsaturated or saturated. Unsaturated oils contain Double bonds between some of the carbons. Monosaturated fats contain one double bond, Polysaturated fats contain more than one double bond.

Unsaturated oils can be hydrogenated making the liquid at room temperature oils harder. They are reacted in the presence of a nickel catalyst at about 60*C, this highers their melting point making them good spreads. Margarine is partially hydrogenated meaning not all the double bonds were broken this makes it cheaper and last longer but contains a lot of trans fats that are bad for health. Saturated fats higher cholestrol and cooking in oil makes food more fattening. 

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Emulsions

Emulsions are made up of droplets of one liquid suspended in another. Oils do not dissolve in water but you can make an emulsion of water and oil. Emulsions are thicker than oil or water and have many uses that depend on their special properties. They provide better texture, coating ability and appearance, for example in salad dressings, ice creams, cosmetics and paints. Generally the more oil the thicker the emulsion, milk has a lot of water and small amount of oil.

Oil and water naturally seperates out but an emulsifier is used to stop this.

The hydrophobic end is attracted to the oil

The hydrophylic end is attracted to water

The oil droplets are repelled by the hydrophilic bit of the emulsifier. Egg yolk is often used as an emulsifier.

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The Earth's structure

The Earth consists of a core, mantle and crust, and is surrounded by the atmosphere. The Earth’s crust and the upper part of the mantle are cracked into a number of large pieces (tectonic plates). The mantle has the properties of a solid but it can flow very slowly. There is radioactive decay in the mantle that creates lots of heat and and energy. The molten minerals in the mantle then expand and become less dens, rising towards the surface before cooling. This creates convection currents that move the tectonic plates.

Wegner's Theory 

He came across work listing very similar fossils on either side of the Atlantic in south America and Africa. He investigated further and found this was true of other continents across oceans. People believed this was because of land bridges across the oceans that had then sunk. Wegner thought that maybe the continents were joined up. He noticed that there were also matching layers in rock between some continents. Wegner said that there was a supercontinent called Pangea 300 milion years ago that drifted apart by  continental drift. However the theory was not accepted as he used inaccurae data and he could not explain how they moved.

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The atmosphere

For 200 million years the atmosphere has been pretty much the same - 80% nitrogen and 20% oxygen.

Origionallly the Earth's surface was molten and any atmosphere would just burn off. When it cooled a thin crust formed and volcanoes formed. They gave off many gasses and steam, the atmosphere was mainly CO2 and some methane and Amonia. The steam then condensed and oceans were formed.

Green Plants and algae evolved and covered the Earth, they took in lots of this CO2 in the atmosphere and gave out Oxygen. When the plants, algae and marine life died they were buried under sediment this meant that much of the carbon was locked up in the sedimentary rocks that have now become fossil fuels and carbonates. The oceans also dissolves CO2 into it.

The build up of oxygen killed early organisms but more complex ones were able to develop. The oxygen also created the ozone layer O3 to protect the earth from harmfull rays from the sun.

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Life on Earth

There are many theories about how life developed on Earth:

The most commonly believed is the primordial soup theory - that the nitrogen hydrogen ammonia and methane rich atmosphere reacted when there was a lightning strike resulting in the formation of amino acids which collected in a body of water, these gradually combined to produce organic matter which developed into living organisms.

Miller and Urey experiment - They used a mixture of water methane ammonia and hydrogen to model the early atmosphere.  They put a high voltage through the gasses to recreate the lightning strike. They then went through a condenser and the water was found to contain organic compounds. this was then heated and 11 different amino acids were found. This provided evidence for the soup theory

Other theories - Meteorites carry amino acids to earth - deep in the oceans

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Comments

GCSE Revison 1234

Very useful revision source.  Thanks very much.

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