C1.1 – The early atmosphere / Information
1.1 / Carbon dioxide, water vapour, ammonia, methane and nitrogen are the gases produced by volcanic activity that formed the Earth’s early atmosphere. Volcanoes release these gases today (and so scientists think the same processes operated in the past).
1.2 / Scientists think the early atmosphere contained little or no oxygen because no oxygen is released from volcanoes and the iron compounds found in the oldest rocks are compounds that would only form in the absence of oxygen (iron sulphide and carbonate). The first rocks containing iron oxide appeared around the same time as organisms that could photosynthesise.
Scientist think Earth’s early atmosphere could have been like Titans (largest moon of Saturn, only known moon with a dense atmosphere) because it is mainly nitrogen (just like Earth’s today). As we do not have much evidence of Earth’s early atmosphere scientists look at Titan, Venus and Mars as they all have volcanoes and there is no life to change their atmosphere unlike Earth’s which has evolved.
1.3 /
- There is a lack of evidence about the early atmosphere; we don’t have samples of the early atmosphere.
- We only know the composition of the atmosphere today.
- It could have been mainly carbon dioxide (like Mars/Venus)
- But it could have been like Titan (mainly nitrogen).
- We can’t test either theory because it would be difficult to collect data that would provide evidence.
- There are some clues in very old rocks (like the iron compounds in a billion year old rocks) but there aren’t many of these rocks and they gives us information only on the oxygen levels, not on how amounts of other gases changed.
- The volcanic theory makes it seem likely that the early atmosphere was mainly carbon dioxide (like Mars/Venus) but that theory cannot explain how nitrogen was added to the atmosphere, so scientists cannot be sure about which theory is correct. There is no strong evidenced to support one particular idea.
1.4 / Condensation of water vapour formed oceans. Water vapour released from inside Earth through volcanoes; Earth initially hot; cooled; water vapour in the atmosphere condensed; formed oceans.
C1.2 – A changing atmosphere / Information
1.5 / The amount of carbon dioxide in the atmosphere was reduced by: carbon dioxide dissolving into the oceans, the inclusion of this dissolved carbon dioxide into marine organisms which eventually formed carbonate rocks. The hot early Earth cooled so that oceans formed and large amounts of carbon dioxide dissolved in the oceans; used by marine organisms to make calcium carbonate shells. Creatures died; remains of marine organisms decay but shells became part of sediment; sediment became sedimentary rock. Plants and algae that absorb carbon dioxide die and decay to form fossil fuels. This carbon is effectively permanently removed from the oceans, so more carbon dioxide can then dissolve.However, as the temperature rises carbon dioxide becomes less soluble, so some carbon dioxide would leave the oceans and enter the atmosphere, making levels in the atmosphere rise.
1.6 / The amount of oxygen in the atmosphere gradually increase because photosynthesising organisms evolved, they released oxygen into the atmosphere, the number of these organisms gradually increased; so more and more oxygen was produced. Algae and plants in the sea and plants on land absorb carbon dioxide for photosynthesis.
C1.3 – Oxygen in the atmosphere / Information
1.7 – Investigate the proportion of oxygen in the atmosphere. / Practical/possible coursework
C1.4 – The atmosphere today / Information
1.8 / Current composition of the atmosphere: Nitrogen (78%), Oxygen (21%), Argon (0.9%), carbon dioxide (0.04%), other gases (traces).
1.9 / Small changes in the atmosphere occur through; Natural activities: Volcanic activity can lead to a rise in sulphur dioxide; lightening can lead to a rise in nitrogen oxides.
Human activity: burning fossil fuels can lead to an increase of carbon dioxide, carbon monoxide and sulphur dioxide. Deforestation can also lead to an increase in carbon dioxide; burning trees releases carbon dioxide (combustion), fewer trees to photosynthesise and absorb carbon dioxide; engines and furnaces release nitrogen oxides. Farming: increasing numbers of cattle and rice fields can lead to an increase of methane.
Scientists could measure how global levels of carbon dioxide are changing by forming a global network of measuring sites and taking a mean. Use sites away from places that could ‘skew’ readings such as volcanoes, factories and cities. Use new technologies such as satellites that measure carbon dioxide levels in the atmosphere. Compare to longer term records since 1800 and look at the rate of increase.
Ice cores are used to find out the concentration of carbon dioxide in the Earth over many years. Air bubbles remain trapped in the ice and it is this air they test to find out the composition of the air. However, changes in the Earth’s climate mean there is no ice over 400,000 years old. When snow falls it gradually gets compacted to a much thinner layer of ice, so ice representing 10 years will be a few mm thick. Making it hard to show short term changes such as year on year. Also air diffuses through spaces in snow until the weight of additional snow squeezes the snow to ice and traps bubbles. This means the ‘age’ shown by the trapped air doesn’t match the real age of the ice layer.
C1.5 – Rocks and their formation / Information
2.1 / Igneous rocks, such as granite, are formed by the solidification of magma or lava and are made of crystals whose size depends on the rate of cooling. Rock inside the Earth can become hot enough to partially melt. Molten rock is called magma, if it stays inside the Earth, lava if it erupts to the surface. When molten rock cools down it solidifies and becomes a solid rock and crystals from. Rocks formed this way are called igneous. Igneous rocks have interlocking crystals, and are harder than sedimentary rocks. Granite is a form of igneous rock and forms from magma cooling slowly to form large crystals. Rhyolite is another form of igneous rock which has smaller crystals, suggesting it cooled quicker. It is likely that granite formed underground from magma and ryholite above ground from lava. Igneous rock may become sedimentary rock if it is broken up and erodes: broken rock builds up in layers and eventually becomes sedimentary rock.
2.2 / Chalk and limestone are sedimentary rocks both mainly contain the compound calcium carbonate. Can be formed from the hard parts of dead organisms (shells – made from calcium carbonate).
2.3 / Sedimentary rocks are formed by the compaction of layers or sediment over a long period of time. Rocks are broken into small pieces by physical processes such as water when it freezes, and by chemical reactions with water or air. Pieces of rock are eroded when they are transportedby a river to the to the sea; pieces of rock build up in layers; over a very long time layers are compacted or squashed together to form new rock. Rocks formed in this way are called sedimentary. Sedimentary rocks may have layers and may contain fossils.
2.4 / Fossils are found in sedimentary rocks but not igneous because animals, plants and their traces build up and are incorporated in layers of sediment as they build up and into the sedimentary rock; any fossils would be destroyed when the rock melted to become the magma needed to form igneous rock. Sedimentary rock can be eroded; they are not as hard as the other rocks as they do not contain interlocking crystals.
2.5 / Marble is a metamorphic rock formed from either limestone or chalk. It contains tiny crystals in coloured bands.
2.6 / Metamorphic rocks are changed rocks with new crystals, formed by the action of heat/pressure. Metamorphic rocks become buried deep underground below the Earth’s surface; rocks are changed by the action of heat and/or pressure, but they do not melt. Metamorphic rocks have interlocking crystals, and are harder than sedimentary rocks. Marble is an example of a metamorphic rock made from chalk or limestone. Grains in chalk and limestone are weakly joined together, with small gaps between them. When marble forms these grains become new crystals of calcium carbonate that interlock tightly. This makes marble harder than chalk or limestone.
2.7 / Marble, chalk and limestone are all natural forms of calcium carbonate and exist in the Earth’s crust.
C1.6– Limestone and its uses / Information
2.8 /
2.9 / Limestone (calcium carbonate) is used widely in the construction industry in the manufacture of gravel, cement, concrete and glass – these are all valuable building materials. If more houses are being made more limestone will be needed. If less limestone was quarried, its cost would increase and so would the cost of building a house.
Limestone is the cheapest to quarry – less waste left at limestone quarry.
Cement is made by: heating limestone with powdered clay.
Concrete made by; mixing cement with sand, gravel and water.
Glass made by; heating limestone with sodium carbonate and sand.
Alternatives to limestone (which is slowly eroded by rain):
Sandstone – it is damaged by bad weather but is easy to cut into shape.
Granite – difficult to cut but is not affected by acid rain or bad weather.
2.10 / Thermal decomposition – using heat to break down calcium carbonate to form calcium oxide and carbon dioxide.
Calcium carbonate calcium oxide + carbon dioxide
C1.7– Thermal decomposition of carbon / Information
2.11 / Practical/possible coursework
C1.8– Chemical reactions / Information
2.12 / Ease of thermal decomposition of metal carbonates: Most difficult to decompose is sodium carbonate (10000C), calcium carbonate (8250C), zinc carbonate (3000C) and copper carbonate (2000C).
Copper carbonate copper oxide + carbon dioxide
CaCO3(s) CaO(s) + CO2(g)
Copper carbonate will start to decompose to form carbon dioxide and copper oxide. The reaction will absorb some of the heat from the fire. The carbon dioxide can help to put out the fire by reducing the amount of oxygen available for combustion.
Copper carbonate copper oxide + carbon dioxide
Zinc carbonate zinc oxide + carbon dioxide
2.13 / An atom is the smallest part of an element that can take part in chemical reactions.During chemical reactions atoms are neither created nordestroyed. The total number and type of atoms is the same before and after a chemical reaction (if in a sealed container). The atoms are just rearranged to form new products with different physical and chemical properties from the reactants. They form compounds which consist of two or more different elements chemically joined together. The number of atoms of each element is the same on both sides of equation.
CuCO3 CuO + CO2
ZnCO3 ZnO + CO2
2Ca + O2 2CaO
2.16 / The total mass of atoms is the same before and after a chemical reaction (if in a sealed container). The atoms are just rearranged to form new products with different properties from the reactants.
C1.9– Reactions of calcium compounds / Information
2.14 and 2.15 / When water and calcium oxide react, a lot of heat is given off; calcium hydroxide (a crumbly white solid) – is made.
Calcium oxide + water calcium hydroxide
CaO (s) + H2O (l) Ca(OH)2 (s)
Calcium hydroxide dissolves when more water is added, forming calcium hydroxide solution (aqueous – aq). The solution is called limewater. Lime water turns cloudy in the presence of carbon dioxide. This is because white insoluble calcium carbonate forms.
Calcium + carbon calcium + water
hydroxide dioxide carbonate
Ca(OH)2(aq) + CO2(g) CaCO3(s) + H2O(l)
2.17 / Calcium hydroxide, oxide and carbonate neutralise soil acidity by reacting with acids in the soil and neutralising them. Some crops do not grow if the soil is too acidic (pH too low); the acidity must be reduced (pH increased) if the crops are to grow.
2.18 / Calcium carbonate can reduce harmful emissions from coal fired power stations by using wet powdered calcium carbonate which reacts with and neutralises the acidic gases, sulphur and nitrogen oxides, produced when fossils fuels e.g. (coal) burn; this stops the acidic gases escaping into the air from the power station chimneys.
C1.10 – Indigestion / Information
3.1 / Hydrochloric acid is produced in the stomach to kill bacteria and to help with digestion. It allows digestive enzymes to work properly.
3.2 / Indigestion is caused by too much stomach acid. Indigestion tablets are a medicine that can neutralise excess stomach acids. They contain bases which are dissolved in water – they are called alkalis.
What causes indigestion;
- The stomach produces acid which kills bacteria and helps with digestion.
- If too much acid is produced it causes the pain we call indigestion
- Indigestion can be cured by neutralising this acid.
- Antacids contain bases such as calcium carbonate that neutralise the acids.
- They contain substances other than calcium carbonate which may be harmful.
- They have not been tested for toxicity.
- Not know how much to use.
- Hard to grind up, may be sharp edges, damage throat or gullet.
C1.11 – Indigestion remedies / Information
3.3 / Practical/possible coursework
C1.12 – Neutralisation / Information
3.4 / Acids are neutralised by metal oxides, hydroxides and carbonates to produce salts and water. A carbonate will produce carbon dioxide when it reacts with an acid; this is a gas and will cause bubbling. Oxidesand hydroxides do not produce a gas when it reacts with an acid. Acids are corrosive. Hazard symbols are used to show the hazards connected with the materials in a container. This allows people to use them safely and helps the emergency services work out how to deal with an accident involving the chemical. Standard symbols are needed so that they can be understood by anyone using the chemicals or having to deal with spills or other accidents, whatever language they speak.
3.5 / Hydrochloric acid produces chloride salts, nitric acid produces nitrate salts and sulphuric acids produce sulphate salts.
Hydrochloric acid + copper oxide copper chloride + water
Nitric acid + sodium hydroxide sodium nitrate + water
Sulphuric acid + copper carbonate copper sulphate + water + carbon dioxide
C1.13 – Electrolysis / Information
3.6 / Electrolysis is the process in which electrical energy, from a d.c. (direct current) supply, decomposes (breaks down) compounds. Electrolysis of hydrochloric acid produces hydrogen and chlorine gas – which are given off at the electrodes shown by bubbles being produced. Compounds that can be decomposed by electrolysis are called electrolytes.
3.7 / Practical/possible coursework
3.8 / Chemical test for hydrogen – hold a lighted splint in the mouth of a test tube containing hydrogen. The mixture of hydrogen and air in the tube will explode with a squeaky ‘pop’.
3.9 / Chemical test for chlorine – hold a piece of damp blue litmus paper in the mouth of a test tube containing chlorine gas. The paper will turn red and then white, as it is bleached. Chlorine is toxic so should not be sniffed. The litmus paper turns red because chlorine dissolves in the water to make an acid.
C1.14 – The importance of chlorine / Information
3.10 / Chlorine can be obtained from sea water by electrolysis. The main salt dissolved in sea water is sodium chloride. Chlorine gas is produced by the electrolysis of sea water. Substances containing chorine all have ‘chloro’ or similar in their name. Bleach (sodium hypochlorite).
3.11 / Chlorine is a toxic gas at room temperature – it is a yellow-green colour. This can lead to potential hazards when it is manufactured on a large scale. Benefits of the large scale production of chlorine are: less illness due to bacteria in drinking water or swimming pool, energy saving because water does not need to be boiled to sterilise it, many uses of plastics such as PVC. Drawbacks: cost of producing the substances needed; possible accidents while handling or using the substances. Risk if there is a leak: illness of death of people breathing the gas or coming in contact with chlorine compounds.
3.12 / Chlorine can be used in the manufacture of bleach and the polymer poly(chloroethene) (PVC). Treating swimming pool water and drinking water to kill bacteria. It is a useful disinfectant because it is toxic so it kills microorganisms. Chlorine compounds that kill bacteria are not harmful when diluted in large volumes of water such as a swimming pool, but are hazardous when in a concentrated form such as containers. So they need hazards symbols such as toxic and harmful.
C1.15 – Electrolysis of water / Information
3.13 / Water can be decomposed to form hydrogen and oxygen by electrolysis. Safety precautions for the electrolysis of water include keep water away from electricity supplies, collect the gas safely and prevent a build up of hydrogen gas as it is extremely flammable. Hydrogen is the lightest gas, so would provide good lift force for airships; it is also cheaper to produce. However airships used helium because hydrogen is flammable and could be dangerous if there was an accident due to the possibility of an explosion.