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The Earth’s sea and atmosphere The Earth’s sea and atmosphere

The Earth’s sea and atmosphere - PowerPoint Presentation

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The Earth’s sea and atmosphere - PPT Presentation

Topic 1 Key Points C11 The early atmosphere When the Earth was young it was very hot and there were lots of volcanoes The gases that escaped from these formed the Earths atmosphere This early atmosphere contained a large amount of carbon dioxide along with some ammonia methane nitroge ID: 653492

key points dioxide carbon points key carbon dioxide water atmosphere metals called metal acid calcium carbonate oxygen atoms reaction rocks gas oil

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Slide1

The Earth’s sea and atmosphere

Topic 1Slide2

Key Points

C1.1 The early atmosphere

When the Earth was young, it was very hot and there were lots of volcanoes. The gases that escaped from these formed the Earth’s atmosphere.

This early atmosphere contained a large amount of carbon dioxide, along with some ammonia, methane, nitrogen and water vapour. There was no oxygen.

As the Earth cooled, water vapour in the atmosphere condensed to form the oceans.

Theories about the sequence of events concerning the Earth’s atmosphere are not certain. Scientists have little evidence and they do not all agree.Slide3

Key Points

C1.2 A changing atmosphere

About half of the atmospheric carbon dioxide in the early atmosphere dissolved in the oceans.

Early marine plants began to photosynthesise – they removed carbon dioxide from the oceans and atmosphere and gave out oxygen. The fairly rapid expansion of plant life on land increased the rate of this. The amount of carbon dioxide in the atmosphere gradually decreased and the amount of oxygen increased.

Some of the dissolved carbon dioxide became part of the shells of marine organisms, such as coral. When these died they sank to the bottom of the ocean and over millions of years formed sedimentary carbonate rocks, such as limestone.Slide4

Key Points

C1.4 The atmosphere today

Scientists monitor the composition of the atmosphere in different places constantly. The main gas in the atmosphere today is nitrogen, which makes up 78% of the atmosphere. Some scientists think that this has built up from the many volcanic eruptions over the lifetime of the Earth.

The second most abundant gas in the atmosphere is oxygen, which makes up 21% of the atmosphere. This is there because of constant photosynthesis by the plants on the planet.

The third most abundant gas is argon, which makes up about 1%. It is a noble gas element and there are smaller amounts of other

unreactive

gases as well.Slide5

Key Points - continued

There is about 0.04% of carbon dioxide in the atmosphere, but human activities such as burning fossil fuels, deforestation, cattle farming and rice growing are thought to be increasing this proportion.Slide6

Materials from the earth

Topic 2Slide7

Key Points

C1.5 Rocks and their formation

Rocks deep inside the Earth can get hot enough to melt – molten rock is called magma. This sometimes escapes to the Earth’s surface – when it erupts it is called lava.

Igneous rocks are formed when magma solidifies – this can happen underground or on the surface of the Earth. These rocks have a crystalline structure – if magma cools slowly, the crystals are bigger than if it cools quickly. Granite is an igneous rock.

Metamorphic rocks are formed when existing rocks are subjected to high temperature and high pressure. Marble is a metamorphic rock formed when underground limestone or chalk are subjected to the right conditions.Slide8

Key Points

Most sedimentary rocks are made from particles of other rocks that have eroded and have been washed away in rivers and laid down to form layers called sediments. The layers pile up and compress the deeper layers of sediment over a very long time period – the particles get cemented together. Sandstone is a sedimentary rock.

The only types of rock that may contain fossils are sedimentary rocks. The sediments may contain dead plants and animals, so the hard parts of these can become trapped in the new sedimentary rock and an impression of their shape is left.Slide9

Key Points

Some sedimentary rocks are made from the hard parts of marine organisms – this is how limestone and chalk are formed. These two rocks contain calcium carbonate – and so does marble because it is made from them.

Sedimentary rocks erode more easily than other types of rock because the particles are only cemented together – they are not made of crystals that interlock strongly.Slide10

Key Points

C1.6 Limestone and its uses

Limestone is an important material and large quantities of it are removed from the Earth in quarries. Explosives are used to break the limestone into pieces. These are cut or crushed and taken to the customers. Some is used in the form of regular blocks for constructing buildings. Much of it is used to make new materials.

Limestone (along with chalk and marble) contains calcium carbonate – when this is heated, it changes to make calcium oxide (lime) and carbon dioxide. This chemical reaction is called thermal decomposition.Slide11

Key Points

Limestone is needed for making cement, concrete and glass. Cement is made by heating limestone with clay. Concrete is made by mixing sand, gravel, water and cement. Glass is made by heating calcium carbonate with sand and sodium carbonate.

Quarries are dusty, unsightly and noisy places. They often happen to be in attractive places and they might harm the tourist industry. They also take up land that could have been used for farming. Decisions have to be made about balancing the need for limestone and the effect that getting it can have on local people, the environment and the economy.Slide12

Key Points

C1.8 Chemical reactions

All substances are made of atoms. An atom is the smallest part of an element that can take part in chemical reactions.

A compound consists of atoms of two or more elements chemically joined together. The chemical formula of a compound shows the symbols of the elements it contains and the ratios in which their atoms are present.

In all chemical reactions, the atoms of the reactants rearrange to form new products. None of the atoms are destroyed in the reaction and no new ones are formed.Slide13

Key Points

Atoms are not made or destroyed in a chemical reaction – they are only rearranged. So the total mass before and after any reaction stays the same.

Word equations show what happens in chemical reactions. In general:

reactants

products

For example, zinc carbonate decomposes on heating – it makes zinc oxide and carbon dioxide:

zinc carbonate

zinc oxide + carbon dioxide

Reactions like this can also be represented by balanced equations:

ZnCO

3

(s)

ZnO

(s) + CO

2

(g)Slide14

Key Points

There are similarities between ‘families’ of compounds. For example, other carbonate compounds decompose on heating, and have similar equations for the reaction – but some need higher temperatures than others. For example, calcium carbonate is more stable than copper carbonate – it needs stronger heating to break it down.

Another kind of chemical reaction is precipitation. This happens when soluble substances react to form an insoluble product, called the precipitate. For example, silver nitrate and potassium bromide are soluble – their solutions react to form insoluble silver bromide:

silver nitrate

(

aq

)

+ potassium bromide

(

aq

)

potassium nitrate

(

aq

)

silver bromide

(s)Slide15

Key Points

C1.9 Reactions of calcium compounds

When water is added to calcium oxide a chemical reaction happens that produces a lot of heat. The solution formed is calcium hydroxide – also called limewater.

When carbon dioxide is bubbled through limewater, it turns cloudy – a precipitate of insoluble white calcium carbonate is formed. This reaction can be used as a test for carbon dioxide – bubble the suspected gas through some limewater, and if the solution turns cloudy then the gas is carbon dioxide.

Acids are neutralised by alkalis – this reaction is called neutralisation. Calcium carbonate, calcium oxide and calcium hydroxide all neutralise acids.Slide16

Key Points

Some crops do not grow well if the soil is too acidic, so farmers sometimes need to reduce the acidity of their soil. They spray powdered calcium carbonate, calcium oxide or calcium hydroxide over their fields to do this.

Nitrogen oxides and

sulphur

dioxide are formed when coal burns – and coal-fired power stations burn a lot of coal. These are acidic gases that can produce acid rain if they escape from the chimneys. Calcium carbonate is sprayed into the chimneys and it neutralises the acidic gases, so reducing the chance of acid rain forming.Slide17

acids

Topic 3Slide18

Key Points

C1.10 Indigestion

Your stomach produces hydrochloric acid to kill bacteria – the acid also helps enzymes to digest the food you eat. If too much acid is produced, you can get indigestion.

Indigestion remedies (antacids) contain substances that neutralise the extra acid. Substances used include calcium carbonate and magnesium hydroxide.

A base is a substance that neutralises an acid to produce a salt and water:

acid + base

salt + water

A base that is soluble in water is called an alkali.Slide19

Key Points

You can describe acids and alkalis using the pH scale, which runs from 0 (highly acidic) to 14 (highly alkaline). A neutral solution (such as water) has a pH of 7.

Indicators such as litmus show acidity (red) and alkalinity (blue) by changing colour. Universal indicator has different colours across the full pH range.Slide20

Key Points

C1.12 Neutralisation

Acids can be neutralised by metal oxides, metal hydroxides or metal carbonates. The general equations for these reactions are:

acid + metal oxide

salt + water

acid + metal hydroxide

salt + water

acid + metal carbonate

salt + water + carbon dioxide

When hydrochloric acid is neutralised it makes chloride salts,

sulfuric

acid makes sulphate salts and nitric acid makes nitrate salts.Slide21

Key Points

Substances have to be carried from one place to another and this can be hazardous. Hazard symbols are used to show the dangers of the substance inside a container – this enables people to know what precautions to take when using the substance, and what to do if there is an accident.Slide22

Key Points

C1.14 The importance of chlorine

Chlorine is a yellow-green gas that is toxic, so there are always safety concerns when it is being made, transported or used.

Electrolysis is the process of decomposing compounds by passing a direct current through an electrolyte.

The electrolysis of sea water produces chlorine because it contains dissolved sodium chloride.

You can test a gas to see if it is chlorine by holding a piece of damp blue litmus paper in it – if the gas is chlorine, the litmus paper will first turn red and then white.Slide23

Key Points

Chlorine compounds are used to disinfect swimming pools and drinking water. Chlorine is also used to make bleach and some plastics, such as PVC.Slide24

Key Points

C1.15 Electrolysis of water

The electrolysis of acidified water produces oxygen and hydrogen.

You can test for hydrogen by putting a lighted splint near the mouth of a test tube containing the gas – there will be a squeaky pop as it reacts with oxygen in the air.

You can test for oxygen by putting a glowing splint into a test tube containing the gas – the splint will burst into flames again.Slide25

OBTAINING AND USING METALS

TOPIC 4Slide26

Key Points

C1.16 Ores

A few metals are found on Earth as

uncombined

elements – these are

unreactive

metals such as gold and platinum. Most metals are extracted from ores dug out of the Earth. An ore is a rock containing compounds from which a metal can be extracted at a profit.

Low reactivity metals are extracted by heating their ores with carbon. Iron is an example of a metal that can be extracted from its ore (for example, haematite) in this way.Slide27

Key Points

High reactivity metals are extracted from their ores by electrolysis – this is expensive because of the amount of energy it takes. An example of a metal that has to be extracted from its ore (bauxite) in this way is aluminium.

The way in which a metal is extracted depends on its reactivity − the more reactive a metal is, the harder it is to extract. The metals can be organised into a reactivity series, which lists metals in order of reactivity. The most reactive metals are at the top and these are the hardest to extract from their ores – and among the most expensive. Metals above zinc in the reactivity series are extracted using electrolysis.Slide28

Key Points

C1.18 Oxidation and reduction

Oxidation is the addition of oxygen to an element or compound; reduction is the removal of oxygen from a compound.

Most ores are oxides of metals. To extract the metal, the metal oxide must lose oxygen – the metal oxide must be reduced. The reduction can be done by heating with carbon or by electrolysis, depending on the reactivity of the metal.

Most metals corrode – the corrosion of iron is called rusting. Corrosion nearly always involves the reaction of the metal with oxygen in the air – this is oxidation.Slide29

Key Points

Metals high in the reactivity series corrode very easily; metals lower down don’t – which explains why gold can be found

uncombined

in some places.

Using a coating of some kind (for example oil or paint) can slow down the rate of corrosion of a metal.Slide30

Key Points

C1.19 Recycling metals

Most metals can be recycled. Used metals are taken to scrap yards where iron and steel are separated from non-magnetic metals using magnets. New products can be made by melting down the old metals are remoulding them.

Three of the main advantages of recycling are:

– reserves of metal ores will last longer

– it reduces the use of energy

– there is less damage to the landscape from mining.

There are some disadvantages including the cost and the energy used in collecting, sorting and transporting metals to be recycled.Slide31

Key Points

C1.20 Properties of metals

Metals are good conductors of heat and electricity. They are strong, hard and can be hammered into shape (malleable). They can also be stretched into wires (ductile).

There are many uses for metals – few examples are:

– aluminium is used to make aircraft because it has a low density

– copper is used to make electrical cables because it is a good electrical conductor and is ductile

– copper is also used to make water pipes because it is malleable and does not react with waterSlide32

Key Points

– gold is used to make jewellery because it is attractive and

unreactive

– steel is used in construction because it is strong and relatively cheap.Slide33

FUELS

TOPIC 5Slide34

Key Points

C1.22 Crude oil

Crude oil is a mixture of different hydrocarbon molecules. This is a thick black mixture trapped in some sedimentary rocks. It is called a fossil fuel because it was formed from the remains of marine plants and animals.

Hydrocarbons are compounds that are made of hydrogen and carbon atoms only. The hydrocarbon molecules in crude oil have different numbers of carbon atoms and hydrogen atoms.

Crude oil will run out one day and it being made much more slowly than we are using it – this means that it is a non-renewable energy resource.Slide35

Key Points

C1.23 Crude oil fractions

Crude oil is a mixture of different compounds, which have different boiling points. The mixture is split up into fractions by fractional distillation. Each fraction is also a mixture of different compounds, but many fewer compounds.

The fractions containing hydrocarbons with the shortest molecules have lower boiling points, lower viscosity (they are runnier) and are easier to ignite (set alight) than fractions containing larger molecules.Slide36

Key Points

Each fraction has different uses. Gases are used for heating and cooking. Petrol is used as a fuel for cars. Kerosene is used as aircraft fuel. Diesel oil is used as a fuel for some cars and trains. Fuel oil is used by ships and is burned in some power stations. Bitumen is used to make roads and to make some roofs waterproof.Slide37

Key Points

C1.24 Combustion

Combustion is an oxidation reaction. When fuels burn in air they combine with oxygen. The products of the reaction are carbon dioxide and water – energy is also released.

Complete combustion occurs when there is plenty of oxygen for the reaction.

Carbon dioxide can be detected using limewater – when carbon dioxide bubbles through it, the limewater turns milky.Slide38

Key Points

C1.25 Incomplete combustion

Incomplete combustion happens when there is not enough oxygen to allow a fuel to burn completely. Incomplete combustion produces water, some carbon dioxide, some carbon monoxide and carbon particles – the carbon particles are also known as soot.

Carbon monoxide is a toxic gas – it reduces the amount of oxygen that a person’s blood can carry. Some faulty boilers produce carbon monoxide. Deaths from carbon monoxide poisoning can be reduced by having boilers serviced regularly, and by using carbon monoxide alarms.Slide39

Key Points

C1.26 Acid rain

Rainwater always has some carbon dioxide dissolved in it, which makes it slightly acidic. Other gases produced in power stations and car engines can also dissolve in water in the air – these gases include

sulfur

dioxide. They make the rain more acidic – rain that is more acidic than normal (less than about pH 5.2) is called acid rain.

Acid rain makes lakes and rivers acidic, which harms fish and other life. It also damages trees, buildings made of limestone or marble, and makes metal corrode.Slide40

Key Points

The amount of acid rain falling in Europe and North America has been reduced by removing

sulfur

from car fuels and by removing

sulfur

dioxide from power station waste gases.Slide41

Key Points

C1.27 Climate change

Carbon dioxide, methane and water vapour in the atmosphere help to keep the Earth warm by trapping heat energy – this is called the greenhouse effect.

Some human activities put more of these gases into the air. Burning fossil fuels gives out carbon dioxide; cows and rice fields give out methane.

There is evidence that the increasing proportion of carbon dioxide in the atmosphere is causing a slow increase in temperature which is leading to climate change.Slide42

Key Points

Scientists could reduce the amount of carbon dioxide in the atmosphere by adding iron to the oceans – this is called iron seeding. It encourages plankton to grow, which use up carbon dioxide as they photosynthesise.

Carbon dioxide can be removed from the atmosphere and used to make hydrocarbons. These could be used as a replacement for fossil fuels.Slide43

Key Points

C1.28

Biofuels

Biofuels

are fuels made from plant or animal waste. Any plant material that is burned is a

biofuel

. They are alternatives to fossil fuels – but the best thing about them is that they are renewable fuels.

Ethanol is a

biofuel

made using sugar cane or sugar beet. It can be mixed with petrol for use in car engines. Using ethanol helps to reduce the demand for petrol, and so conserves crude oil supplies.

Biodiesel is made from vegetable oils like rapeseed oil and used cooking oil from restaurants. Ordinary diesel engines can run on biodiesel or on a mixture of biodiesel and normal diesel oil.Slide44

Key Points

Using

biofuels

may also help to reduce the overall amount of carbon dioxide that human activity puts into the atmosphere. When plants photosynthesise, they use carbon dioxide from the air. When a

biofuel

burns, it releases carbon dioxide back into the atmosphere. If the burning fuel emits the same amount of carbon dioxide as the plants absorbed, it is carbon neutral.

However, energy is needed to make fertilisers to help the plants to grow, to harvest the crops and to make the

biofuel

. At the moment this energy comes from fossil fuels, so burning

biofuels

can add carbon dioxide to the atmosphere overall.

Another disadvantage is that growing crops to make into

biofuels

reduces the amount of land that can be used to grow food.Slide45

Key Points

C1.29 Choosing fuels

Different fuels have different properties. A good fuel will burn easily producing a lot of heat energy, and it will not produce much pollution. It will also be easy to store and to transport.

Hydrogen produces only water when it burns in air – it also releases a lot of energy per kilogram. However, hydrogen is more difficult to store than petrol or diesel because it is a gas that must be compressed. It is also potentially more dangerous.

Hydrogen and oxygen can also be combined in a fuel cell to produce electricity. Cars and buses can be powered by fuel cells. Before cars with fuel cells can become widely used, hydrogen has to be easily and economically available.Slide46

Key Points

Petrol, kerosene and diesel are all non-renewable fossil fuels. Methane is a non-renewable fossil fuel found in natural gas.

Coal is a non-renewable fossil fuel that produces a lot of ash when it burns.Slide47

Key Points

C1.31

Alkanes

and alkenes

The forces of attraction holding atoms together in a molecule are called bonds.

Alkanes

are hydrocarbons that have only single bonds between carbon atoms. They are called saturated molecules – methane, ethane and propane are all

alkanes

.

Alkenes are hydrocarbons that have at least one double bond between carbon atoms. They are unsaturated molecules –

ethene

and

propene

are alkenes.

A molecule of methane has one carbon atom and four hydrogen atoms – its formula is CH

4

. The formula of ethane is C

2

H

6

; propane is C

3

H

8

.Slide48

Key Points

A molecule of

ethene

has two carbon atoms and four hydrogen atoms – its formula is C

2

H

4

;

propene

is C

3

H

6

.

Bromine water is used to test for alkenes. It is an orange colour – if it is mixed with an unsaturated hydrocarbon, it reacts and the mixture becomes colourless. There is no reaction if bromine water is mixed with a saturated hydrocarbon.Slide49

Key Points

C1.32 Cracking

Most crude oils contain more large hydrocarbon molecules than small ones – and small ones (like those in the petrol fraction) are more useful than larger ones.

Cracking is used to split up long hydrocarbon molecules into shorter ones. Cracking is a thermal decomposition reaction that produces a mixture of molecule lengths, and also a mixture of saturated and unsaturated hydrocarbons –

alkanes

and

alkenes.Slide50

Key Points

Liquid paraffin can be cracked in the laboratory. Mineral wool is soaked in paraffin and put into a boiling tube and is heated. The tube is held horizontally so that the paraffin vapour can pass over pieces of heated porous pot. The gases produced are collected over water.Slide51

Key Points

C1.33 Polymerisation

Lots of small unsaturated molecules, such as

ethene

, can be joined together to form very long molecules called a polymer – this is polymerisation. The repeating units are called monomers. The polymer made from

ethene

is called poly(

ethene

).

Some polymers occur naturally – for example proteins and cellulose. Manufactured polymers are often called plastics.

Poly(

ethene

) is flexible, cheap and a good insulator. It is used for making plastic bags, cling film and insulation for electrical wires.

Poly(

propene

) is flexible and tough, and has a higher melting point. It is used to make buckets and bowls.Slide52

Key Points

Poly(

chloroethene

) is also called PVC – it is tough and cheap. It is used to make window frames, gutters and pipes.

PTFE is also called Teflon® – it is tough, slippery and resistant to corrosion. It is used to make non-stick pans, containers for corrosive chemicals and stain-proof carpets.Slide53

Key Points

C1.34 Problems with polymers

Manufactured polymers are not biodegradable – this means that they do not rot. This is a useful property because it means that things made from polymers last a long time. However, it also means that they do not decompose when they are thrown away – they will last for thousands of years in landfill sites.

There is a big landfill problem – there is too much of it. There are ways of reducing the problem. For example, plastic waste can be incinerated and the energy used to generate electricity. However, some polymers produce toxic gases when they burn and these must be removed from the waste gases.Slide54

Key Points

Another development is that scientists are developing biodegradable polymers that will rot relatively quickly when they are thrown away.

A better way of tackling the landfill problem is to reduce the amount of waste that needs to be dealt with by reusing items when we can. When we have finished with an object it can be recycled. Plastic objects that can be recycled have a symbol stamped on them to show the type of polymer they are made from.