Chemistry (C1)

Anmerkungen:

• This is VERY basic stuff, involving how to write equations, and the basic structure of the atom.  SEE C2 for this detail. 

1. Atomic structure

   Anmerkungen:

   • -Protons and neutrons make up the nucleus. -Electrons orbit the nucleus. 
   1. Charges

      Anmerkungen:

      • -Electrons are -1. -Neutrons are 0. -Protons are 1.
2. Atomic number

   Anmerkungen:

   • The amount of protons (and electrons) and atom has. 
3. Mass number

   Anmerkungen:

   • The amount of particles in an atom: protons + neutrons. 
   1. Particle weight

      Anmerkungen:

      • -Electrons are 0. -Neutrons are 1. -Protons are 1. 

1. Limestone and its uses
   1. Uses

      Anmerkungen:

      • -Blocks of limestone can be used for building. -Make calcium oxide. -Make cement.
      1. Concrete

         Anmerkungen:

         • Made by mixing cement with sand. aggregate and water.
   2. Reaction

      Anmerkungen:

      • Calcium carbonate → calcium oxide + carbon dioxide CaCO₃ → CaO + CO₂
      1. Type

         Anmerkungen:

         • This type of reaction is called: thermal decomposition (breaking down by heating).
2. Reactions of carbonates

   Anmerkungen:

   • Metal carbonates decompose when heated to produce the metal oxide and carbon dioxide.
   1. With an acid

      Anmerkungen:

      • Carbonates react with acids to produce: salt, water and carbon dioxide. 
      1. Acid rain

         Anmerkungen:

         • Limestone is damaged by acid rain because the calcium carbonate in the limestone reacts with acids in the rain.
   2. Limewater

      Anmerkungen:

      • -Calcium hydroxide. -Used to test for carbon dioxide. -Turns cloudy because it reacts with carbon dioxide to produce insoluble calcium carbonate.
   3. Decomposition

      Anmerkungen:

      • When metal carbonates are heated strongly enough to decompose, the metal oxide and carbon dioxide are produced.
      1. Energy

         Anmerkungen:

         • A Bunsen burner flame cannot get hot enough to decompose: -Sodium carbonate. -Potassium carbonate.
3. Limestone cycle

   Anmerkungen:

   • -Thermal decomposition of calcium carbonate produces calcium oxide and carbon dioxide. -Calcium oxide reacts with water to produce calcium hydroxide. -Calcium hydroxide is an alkali that can be used to neutralize acids. -Calcium hydroxide reacts with carbon dioxide to produce calcium carbonate.  
4. Cement and concrete
   1. Cement

      Anmerkungen:

      • -To make cement, limestone is mixed with clay and heated strongly in a kiln.  -The product is ground up to make a fine powder.
   2. Mortar

      Anmerkungen:

      • -Cement is mixed with sand and water to make mortar. -The mortar is used to hold bricks and blocks together in buildings. 
   3. Concrete

      Anmerkungen:

      • Concrete is made by mixing aggregate with cement, sand and water.
      1. Aggregate

         Anmerkungen:

         • Small stones or crushed rock are used as aggregate.
5. Limestone issues
   1. Advantages

      Anmerkungen:

      • -We rely on limestone products for building materials. -More employment opportunities for local people. -More customers and trade for local businesses. -Improved roads.
   2. Disadvantages

      Anmerkungen:

      • -Dust and noise. -More traffic. -Loss of habitats for wildlife. 

1. Extracting metals

   Anmerkungen:

   • Metals are usually found in the Earth's crust. They are often combined chemically with other elements such as oxygen.
   1. Ore

      Anmerkungen:

      • An ore contains enough metal to make it worth extracting the metal.
      1. Cons

         Anmerkungen:

         • These processes can produce: -Large amounts of waste. These can have BIG impacts on the environment. 
         • These processes can produce: -Large amounts of waste. These can have BIG impacts on the environment. 
   2. Reactivity series

      Anmerkungen:

      • -Very unreactive metals, low in the reactivity series, are found in the Earth as a metal. -Gold can be separated by physical means. -Most metals are found as compounds. -This means that metals have to be extracted chemically.
   3. Displacement

      Anmerkungen:

      • Metals can be extracted by displacement using a more reactive element.
      1. Reduction

         Anmerkungen:

         • -If an element is less reactive than carbon, it can be extracted by heating the oxide with carbon. -In this reaction, the carbon removes the oxygen from the oxide to produce the metal. -This is used commercially when possible.
2. Iron and steels
   1. Reduction of iron

      Anmerkungen:

      • -Many of the ores used to produce iron contain iron(III) oxide. -Iron(III) oxide is reduced at high temperatures in a blast furnace using carbon. -Iron produced is about 96% pure -Impurities make it hard and brittle and so it has only a few uses as cast iron. -Removing ALL iron and impurities = pure iron. -Pure iron is too soft for many uses.
   2. Steels

      Anmerkungen:

      • -MOST iron is used to make steels. -Steels are alloys of iron. -They contain mixtures of iron with carbon and other elements. -Alloys can be made so that they have properties for specific uses.
      1. Types

         Anmerkungen:

         • -Amounts of carbon and other elements are carefully adjusted when making steels. -Low-carbon steels = easily shaped. -High-carbon steels = hard.
      2. Stainless

         Anmerkungen:

         • -Stainless steels contain larger quantities of other metals. -They RESIST corrosion.
3. Aluminium and titanium
   1. Aluminium

      Anmerkungen:

      • -Low density. -Resistant to corrosion (despite being high in reactivity series). -More reactive than carbon - electrolysis. -Process requires A LOT of electricity and high temperatures (molten state). -Very expensive to extract. -Pure aluminium IS NOT strong. -Aluminium alloys are stronger and harder.
   2. Titanium

      Anmerkungen:

      • -Resistant to corrosion. -Strong. -Low density compared to other strong metals. -Titanium oxide can be reduced by carbon. -Metal reacts with carbon making it brittle. -Extracted from its ore by a process that involves several stages and LARGE amounts of energy. -The high costs of the process makes titanium expensive.
4. Extracting copper

   Anmerkungen:

   • Copper can be extracted from copper-rich ores by smelting (heating strongly in a furnace).
   1. Smelting

      Anmerkungen:

      • -Smelting produces impure copper, which can be purified by electrolysis. -Smelting and purification require a LARGE amount of energy (heating and electricity).
   2. Copper rich ores

      Anmerkungen:

      • -A limited resource. -Scientists are developing new ways to extract copper form low-grade ores. -These methods can have less environmental impact than smelting.
   3. Phytomining

      Anmerkungen:

      • -Uses plants to absorb copper compounds from the ground. -Plants are burned. -Produce ash. -Copper extracted from ash.
   4. Bioleaching

      Anmerkungen:

      • Uses bacteria to produce solutions containing copper compounds.
   5. Displacement

      Anmerkungen:

      • -Solutions of copper compounds can be reacted with a metal that is more reactive than copper. -This displaces the copper.
   6. Electrolysis

      Anmerkungen:

      • Copper is extracted from solutions of copper compounds by electrolysis.
5. Useful metals
   1. Transition metals

      Anmerkungen:

      • -Central block of periodic table. -Good conductors of heat. -Good conductors of electricity. -Many are strong but can be bent or hammered into shape. -Useful as materials for: buildings, vehicles, containers, pipes and wires.
   2. Copper

      Anmerkungen:

      • -Very good conductor of heat. -Does not react with water. -Can be bent but is hard enough to keep its shape. -These properties make it useful for: making pipes and tanks in water, heating systems. -Good conductor of electricity. -Useful for electrical wiring.
   3. Other metals

      Anmerkungen:

      • -Most metals are not pure elements. -Pure iron, copper, gold and aluminium are soft and easily bent. -Often mixed with other elements to make alloys that are harder so that they keep their shape. -Iron is made into steels. -Copper allows include bronze and brass.
6. Metallic issues
   1. In construction
      1. Benefits

         Anmerkungen:

         • -They are strong. -They can be bent into shape. -They can be made into flexible wires. -They are good electrical conductors.
      2. Drawbacks

         Anmerkungen:

         • -Obtaining metals from ores causes pollution and uses up limited resources. -Metals are more expensive than other materials such as concrete. -Iron and steel can rust.

1. Fuels from crude oil

   Anmerkungen:

   • -Crude oil contains many different compounds that boil at different temperatures. -These burn under different conditions and so crude oil needs to be separated to make useful fuels.
   1. Distillation

      Anmerkungen:

      • We can separate a mixture of liquids through distillation. 
      1. Fractions

         Anmerkungen:

         • -Fractions are liquids that boil within different temperature ranged. -This is from the simple distillation of crude oil.
   2. Hydrocarbons

      Anmerkungen:

      • -Most of the compounds in crude oil are hydrocarbons. -Molecules contain ONLY hydrogen and carbon.
      1. Alkanes

         Anmerkungen:

         • CnH2n+2
         1. Features

            Anmerkungen:

            • -Alkanes contains AS MANY hydrogen atoms as they can. -These are called saturated hydrocarbons.
2. Fractional distillation

   Anmerkungen:

   • -Crude oil is separated into fractions at refineries using fractional distillation. -This is possible as different hydrocarbons have different sized molecules.
   1. Size of molecule

      Anmerkungen:

      • -The larger the molecule, the higher the boiling point of the hydrocarbon.
   2. Fractions

      Anmerkungen:

      • -Fractions with low boiling ranges have low viscosity so they are runny liquids. -Very flammable so they ignite easily. -Also burn with CLEAN flames. -This produces little smoke. -Makes them VERY useful for fuels.
3. Burning fuels
   1. Complete combustion

      Anmerkungen:

      • -When pure hydrocarbons burn completely, they are oxidised. -This produces carbon dioxide and water.
   2. Incomplete combustion

      Anmerkungen:

      • -Limited air supply. -May produce carbon monoxide. -Carbon may also be produced. -Some of the hydrocarbons may not burn. -Produces solid particles that contain soot (carbon). -Also particulates (unburnt hydrocarbons).
   3. Fossil fuels

      Anmerkungen:

      • -Most contain sulfur compounds. -When the fuel burns, the compounds produce sulfur dioxide. -Sulfur dioxide causes rain.
      • -Most contain sulfur compounds. -When the fuel burns, the compounds produce sulfur dioxide. -Sulfur dioxide causes rain.
   4. Nitrogen oxides

      Anmerkungen:

      • -At high temperatures when the fuel is burning, oxygen and nitrogen in the air may combine to form nitrogen oxides. -This causes acid rain.
4. Cleaner fuels

   Anmerkungen:

   • -We burn large amounts of fuels. -This releases substances that spread throughout the atmosphere and affect the environment.
   1. Carbon dixoide

      Anmerkungen:

      • -Any fuel that contains carbon, when burned, produces CO2. -CO2 is a greenhouse gas. -Believed to be the cause of global warming. -Incomplete combustion of these fuels produces the poisonous carbon monoxide. -Also produces particulates which causes global dimming.
   2. Removing harmful substances

      Anmerkungen:

      • -We can remove harmful substances from waste gases before they are released into the atmosphere.
      1. Sulfur dioxide

         Anmerkungen:

         • -Sulfur can be removed from fuels before they are burned so less sulfur dioxide is given off.
      2. Exhaust systems

         Anmerkungen:

         • -Fitted with catalytic converters to remove carbon monoxide and nitrogen oxides. -Filters can remove particulates.
5. Alternative fuels
   1. Biofuels

      Anmerkungen:

      • Made from plant or animal produces and are renewable.
   2. Biodiesel

      Anmerkungen:

      • Made from vegetable oils extracted from plants.
      1. Advantages

         Anmerkungen:

         • -Little contribution to carbon dioxide levels. -This is because the CO2 given off when it burns was taken from the atmosphere by plants as they grew.
      2. Disadvantages

         Anmerkungen:

         • Plants that are grown for biodiesel use large areas of farmland.
   3. Ethanol

      Anmerkungen:

      • -Made from sugar cane or sugar beet. -A biofuel. -It is liquid and so can be stored and distributed like other liquid fuels. -Can be mixed with petrol.
   4. Hydrogen

      Anmerkungen:

      • Hydrogen can be used as a fuel.
      1. Advantages

         Anmerkungen:

         • Only produces water when burned.
      2. Disadvantages

         Anmerkungen:

         • -It is a gas so takes up a large volume. -This makes it difficult to store in the quantities needed for combustion in engines. -Can be produced from water through electrolysis, but this requires A LOT of electricity.

1. Cracking hydrocarbons
   1. Cracking

      Anmerkungen:

      • Large hydrocarbon molecules can be broken down into smaller molecules by a process called cracking.
      1. Processes

         Anmerkungen:

         • -By heating a mixture of hydrocarbon vapours and steam to a very high temperature. -By passing hydrocarbon vapours over a hot catalyst.
   2. Alkenes

      Anmerkungen:

      • CnH2n
      1. Features

         Anmerkungen:

         • -They contain fewer hydrogen atoms than alkanes BUT the same number of carbon atoms. -They are unsaturated hydrocarbons.
      2. Bonds

         Anmerkungen:

         • -Alkenes have a double bond between two carbon atoms. -This makes them MORE reactive than alkanes.
      3. Bromine water

         Anmerkungen:

         • -Alkenes react with bromine water turning it from orange to colourless.
2. Making polymers from alkenes
   1. Plastics

      Anmerkungen:

      • Plastics are made from very large molecules called polymers.
      1. Polymers

         Anmerkungen:

         • Made from many small molecules joined together.
         1. Monomers

            Anmerkungen:

            • The small molecules used to make polymers.
            1. Polymerisation

               Anmerkungen:

               • The reaction to make a polymer.
   2. Polymerisation of ethene

      Anmerkungen:

      • -Lots of C2H4 molecules join together to form polythene. -In the reaction. the double bond in each ethene molecule becomes a single bond. -Thousands of ethene molecules join together in long chains.
   3. In life

      Anmerkungen:

      • Many of the plastics we use as bags, bottles, containers and toys are made from alkenes.
3. New and useful polymers

   Anmerkungen:

   • -New polymers are being developed all the time. -Polymers are designed to have properties that make them specially suited for certain uses. -We are now recycling more plastics and finding more uses for them.
   1. Smart polymers

      Anmerkungen:

      • Shape memory polymers which change back to their original shape when temperature or other conditions are changed.
      1. Example

         Anmerkungen:

         • A material used for stitching wounds that changes shape when heated to body temperature.
   2. Hydrogels

      Anmerkungen:

      • Polymers that can trap water and have many uses including dressings for wounds.
   3. Light-sensitive polymers

      Anmerkungen:

      • Used in sticking plasters to cover wounds so the plasters can be easily removed.
4. Plastic waste

   Anmerkungen:

   • -Many polymers are not biodegrabable. -Plastic waste is not broken down when left in the environment. 
   1. Problems

      Anmerkungen:

      • -Unless disposed of properly, plastic rubbish gets everywhere. -It is unsightly. -It can harm wildlife. -When put into landfill sites, it takes up valuable space.
   2. Biodegradable plastics

      Anmerkungen:

      • -We are using more plastics that are biodegradable. -Microorganims can break down biodegradable plastics. -These plastics break down when in contact with the soil.
   3. Cornstarch

      Anmerkungen:

      • -Mixed with plastics. -Microorganisms can break down cornstarch. -Plastic breaks into very small pieces. -These pieces can be mixed with soil or compost.
   4. Recycling

      Anmerkungen:

      • -Some plastics can be recycled. -There are MANY different types of plastics. -Sorting is difficult.
5. Ethanol

   Anmerkungen:

   • -Has the formula C₂H₆O. -Often written as: C₂H₅OH. -The OH shows that it is an alcohol molecule.
   1. Fermentation

      Anmerkungen:

      • -Ethanol can be produced by the fermentation of sugar from plants using yeast. -Enzymes in the yeast cause the sugar to convert to ethanol and carbon dioxide. -This method is used to make alcoholic drinks.
      1. Reaction
      2. Source

         Anmerkungen:

         • Ethanol produced by fermentation uses a renewable resource, sugar from plants.
      3. Conditions

         Anmerkungen:

         • -Done at room temperature. -Fermentation can only produce a dilute aqueous solution of ethanol. -Ethanol MUST be separated from the solution by fractional distillation to give pure ethanol.
   2. Hydration of ethene

      Anmerkungen:

      • -Ethanol can be produced by the hydration of ethene. -Ethene is reacted with steam at a high temperature in the presence of a catalyst.  -The ethene is obtained from crude oil by cracking.
      1. Reaction
      2. Source

         Anmerkungen:

         • Ethanol produced from ethene uses a non-renewable resource, crude oil.
      3. Conditions

         Anmerkungen:

         • -Reaction can be run continuously and produces pure ethanol. -Requires a high temperature.

1. Extracting vegetable oil
   1. Vegetable oils

      Anmerkungen:

      • Vegetable oils can be extracted from seeds, nuts and fruits by pressing or by distillation.
      1. Distillation

         Anmerkungen:

         • Some oils are extracted by distilling the plant material mixed with water.
      2. Product

         Anmerkungen:

         • These processes produce a mixture of oil and water from which the oil can be separated.
   2. Uses

      Anmerkungen:

      • -When eaten, vegetable oils provide us with a lot of energy and important nutrients. -Also release a lot of energy when they burn in the air and so can be used as fuels. -They are used to make biofuels such as biodiesel. 
   3. Molecule

      Anmerkungen:

      • -Have hydrocarbon atoms. -Those with carbon-carbon double bonds (C=C) are unsaturated. -Several double bonds in each molecule = polyunsaturated.
      1. Unsaturated oils

         Anmerkungen:

         • These react with bromine water, turning it from orange to colorless. 
2. Cooking with vegetable oils
   1. Boiling points

      Anmerkungen:

      • -Boiling points of vegetable oils are higher than water. -Food is cooked at higher temperatures in oil. -Causes it to cook faster. -Some of the oil is absorbed and so the energy content of the food increases.
   2. Hydrogenation

      Anmerkungen:

      • This involves unsaturated oils being reacted with hydrogen so that some or all of the carbon bonds become single bonds.
      1. Conditions

         Anmerkungen:

         • Done at 60°C using a nickel catalyst.
      2. Hydrogenated oils

         Anmerkungen:

         • These have higher melting points because they are MORE saturated.
      3. Hardening

         Anmerkungen:

         • -This is hydrogenation. -This is because the hydrogenated oils are solids at room temperature. -This is so that they can be used as spreads and to make pastries and cakes that require solid fats.
3. Everyday emulsions
   1. Emulsions

      Anmerkungen:

      • Oils do not dissolve in water but oils and water can be used to produce emulsions. They have SPECIAL properties.
      1. Properties

         Anmerkungen:

         • -Opaque. -Thicker than the oil and water they are made from. -This improves their texture, appearance and their ability to coat and stick to solids.
      2. Examples

         Anmerkungen:

         • -Milk, cream, salad dressings and ice cream. -Water-based paints. -Cosmetic creams.
   2. How they work
      1. Molecules

         Anmerkungen:

         • -A small hydrophilic part. -A long hydrophobic part.
         1. Hydrophilic

            Anmerkungen:

            • -This part or 'head' is attracted to water.
         2. Hydrophobic

            Anmerkungen:

            • -This part or 'tail' is attracted to oil.
      2. The process

         Anmerkungen:

         • -The hydrophobic parts of many emulsifier molecules go into each oil droplet. -The droplets become surrounded by the hydrophilic parts. -This keeps the droplets apart in the water, preventing them from joining together and separating out.
4. Food issues
   1. Advantages

      Anmerkungen:

      • -Vegetable oils are high in energy and provide nutrients. -Vegetable oils are believed to be better for your health than saturated fats. -Emulsifiers improve the texture of foods enabling water and oil to mix.
   2. Disadvantages

      Anmerkungen:

      • -Emulsifiers make fatty foods more palatable and therefore can cause overconsumption. -Animal fats and hydrogenated oils contain saturated fats. -Saturated fats have been linked to heart disease.

1. Structure of the Earth

   Anmerkungen:

   • -Earth is almost spherical. -Diameter ≈ 12800 km.
   1. Crust

      Anmerkungen:

      • -At the surface (thin and solid). -Varies in thickness between about 5km and 70km.
   2. Mantle

      Anmerkungen:

      • -Under the crust. -About 3000km thick. -Almost goes halfway to the centre of the Earth. -Mantle is almost entirely solid but parts of ti can flow VERY slowly.
   3. Core

      Anmerkungen:

      • -About half the diameter of the Earth. -High proportion of the magnetic metals iron and nickel. -Has a liquid out part and a solid inner part.
   4. Atmosphere

      Anmerkungen:

      • -Surrounds the Earth. -Most of the air is within 10km of the surface. -Most of the atmosphere is within 100km of the surface.
   5. Resources

      Anmerkungen:

      • -All raw materials and other resources that we depend on come from the crust, oceans and atmosphere. -This means the resource available to us are LIMITED!
2. The restless Earth
   1. Tectonic plates

      Anmerkungen:

      • These are the massive pieces of cracked crust and upper part of the mantle.
      1. Convection currents

         Anmerkungen:

         • Tectonic plates move a few centimetres a year because of convection currents in the mantle beneath them.
         1. Caused by

            Anmerkungen:

            • Convection currents are caused by energy released by the decay of radioactive elements heating up the mantle. 
   2. Earthquakes

      Anmerkungen:

      • -Where the plates meet, huge forces build up. -Eventually the rocks give way. -Changing shape or moving suddenly causing earthquakes, volcanoes or mountains to form. 
      1. Predictions

         Anmerkungen:

         • Scientists do not know enough about what is happening inside the earth to make accurate predictions as to when earthquakes or volcanic eruptions will happen.
   3. Wegener's theory

      Anmerkungen:

      • -Proposed the idea of continental drift. -Stated that 300 million years ago there was one 'supercontinent'. -This was called Pangea. -Pangea broke into smaller chunks (our continents). -These chunks were still 'drifting' apart (even now).
      1. Acceptance

         Anmerkungen:

         • -Idea not accepted by many scientists. -This is because he couldn't explain why the continents moved. -Scientists believed that the Earth was shrinking as it cooled (at the time). -In the 1960s, scientists found new evidence and the theory of plate tectonics was developed.
3. The Earth's atmosphere in the past
   1. When the Earth was formed

      Anmerkungen:

      • -Scientists believe that the Earth was formed 4.5 billion years ago. -In the first billion years the surface was covered with volcanoes that released carbon dioxide, water vapour and nitrogen. 
   2. Early atmosphere

      Anmerkungen:

      • -Most of the water vapour condensed to form our oceans. -Early atmosphere was mainly carbon dioxide with some water vapour. -Some believed that there was also nitrogen and possibly some methane and ammonia.
   3. Next two billion years

      Anmerkungen:

      • -Bacteria, algae and plants evolved. -Algae and plants used carbon dioxide for photosynthesis and this released oxygen. -As the number of plants increased, the amount of carbon dioxide in the atmosphere decreased and the amount of oxygen in the atmosphere increased.
4. Life on Earth

   Anmerkungen:

   • -The plants that produced the oxygen in the atmosphere probably evolved from simple organisms like plankton and algae in the ancient oceans. -We DO NOT know how the molecules of the simplest living things were formed. -Many theories on how life began but there is a lack of evidence to prove it.
   1. Miller-Urey experiment

      Anmerkungen:

      • -Did an experiment based on what scientists thought was in the early atmosphere. -They used a mixture of water, ammonia, methane and hydrogen and a high voltage spark to simulate lightning. -After a week, they found amino acids, which are the building blocks for proteins.
   2. Other theories

      Anmerkungen:

      • Since the 1950s theories about what was in the early atmosphere have changed, but amino acids have been produced using other mixtures of gases.
      1. Primordial soup

         Anmerkungen:

         • One theory suggests that these organic molecules formed a 'primordial soup' and that the amino acids in this mixture combined to make proteins from which life began. 
      2. Problem

         Anmerkungen:

         • MANY other theories have been proposed BUT there is no evidence that proves any of them.
5. Gases in the atmosphere

   Anmerkungen:

   • -Plants took up much of the CO2 in the Earth's early atmosphere. -Animals ate the plants much of the CO2 ended up in plant and animal remains as sedimentary rocks and fossil fuels.
   1. Limestone

      Anmerkungen:

      • Limestone was formed from the shells and skeletons of marine organisms.
   2. Fossil fuels

      Anmerkungen:

      • Fossil fuels contain carbon and hydrogen from plants and animals.
   3. Carbon dioxide

      Anmerkungen:

      • -Carbon dioxide dissolves in the oceans. -Some probably formed insoluble carbonate compounds that were deposited on the seabed and became sedimentary rocks.
   4. Fractional distillation of air

      Anmerkungen:

      • -Gases in air have different boiling points. -Can be separated through fractional distillation. -F.D. of liquid air is done industrially to produce pure oxygen and liquid nitrogen. -Air is cooled to -200°C and fed into an F.D column. -Nitrogen is separated from oxygen and argon and further distillation is used to produce pure oxygen and argon.
   5. 200 million years ago

      Anmerkungen:

      • -The proportions of gases in the atmosphere had stabilised and were much the same as today. -Atmosphere: --20% is oxygen. --Just under 80% is nitrogen. --Other gases, including CO2, water vapour and noble gases, make up 1%.
6. Carbon dioxide in the atmosphere

   Anmerkungen:

   • -For about 200 million years, the amount of carbon dioxide in the atmosphere has remained about the same. -This is because various natural processes that move carbon dioxide into and out of the atmosphere had achieved a balance.
   1. Natural processes

      Anmerkungen:

      • These process involve carbon compounds in plants, animals, the oceans and rocks. 
   2. Oceans

      Anmerkungen:

      • -Carbon dioxide dissolves in water. -This reaction causes inorganic carbonate compounds to form. -This is important in maintaining a balance.
   3. Human activity

      Anmerkungen:

      • -In recent years, the amount of CO2 released into the atmosphere by humans has increased DRAMATICALLY. -Mainly caused by the large increase in the amount of fuels that we burn.
   4. The organic carbon cycle