2480711
Description
Flashcards by Chima Power, updated more than 1 year ago
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Created by Chima Power
over 9 years ago
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| Question | Answer |
| Atoms, elements and compounds | All substances made of atoms about 100 different atoms in the world. Substances made up of one type of atom are elements there are about 100 different types of elements. Elements have different properties like gold is shiny and chlorine is a gas. |
| Atoms and their own symbols | Scientific work is internationals so must have symbols for elements everyone can understand can see these symbols on periodic table. Symbols in periodic table represent oxygen ex. 0 represents atom of oxygen. Elements are arranged in columns called groups with each group containing elements with similar chemical properties. Bold line divides metal and non-metals, elements on left are metals those on right are non-metals. |
| Compounds | Substances made up of two different atoms chemically bonded together are compounds, chemical bonds hold atoms closely together in compounds. Some made up of just two atoms others are more. An atom is made up of a central nucleus and surrounding electrons. |
| Atomic structure | In middle of atom is small nucleus, contains two types of particles: protons and neutrons, a third particle orbits the nucleus these really tiny particles are electrons. Any atom has the same number of electrons as protons. Protons have a positive charge neutrons have no charge so are neutral so nucleus has overall positive charge. Electrons orbiting nucleus are negatively charged relative charge of proton is +1 while negative charge of electrons is -1. As any atom contains equal number of protons and electrons charge cancel out, so no overall charge charge is zero. |
| Atomic number and periodic table | All atoms of particular element have same number of protons, call number of protons the atomic number. Elements in periodic table are arranged in their order of their atomic number. Read periodic table from left to right from up to down. |
| Mass number | Number of protons + neutrons in nucleus of atom is the mass number. number of neutrons = mass number - atomic number |
| Arrangement of electrons in atoms | In model of atom have electrons arranged around the nucleus in shells, like layers of onion. Each shell represents a different energy level, lowest energy level are those shells closest to the nucleus. Electrons in atom occupy the lowest available shell. |
| Electron shells | Energy level (or shell) can only hold certain number of electrons - First and lowest energy level holds 2 electrons - Second energy level can hold 8 electrons - Third energy level can hold 8 electrons and so continues. Writing the number of electrons in energy levels is electronic structure sodium has 2,8,1. |
| Electrons and periodic table | In a group in a periodic table the elements have the same amount of electrons on their highest energy level. Electrons called outer electrons as are on outermost shell hence all elements in Group 1 have one electron on their highest level. Chemical properties of an element depend on how many electrons it has the way electron reacts depends on how many electrons it has on its outermost shell. Some elements in same group with same number of electrons on outermost shell react in the same way. Elements in Group 0 are noble gases as unreactive atoms have stable arrangement of electrons have 8 electrons on outermost shell or in the case of helium which has 2. |
| Forming bonds | Atoms react together by either transferring electrons to form chemical bonds which occurs when metals react with non-metals if reacting atoms are all non-metals the atoms share electrons to form chemical bonds. |
| Forming ions | When metal bonds with non-metal metal atom gives off one or more electrons to non-metal, both atoms become charged particles - ions. - metal atoms form positively charged ions (+) - non-metal atoms form negatively charged ions (-) Opposite charges attract each other, strong attraction between positive and negative ions in compound of a metal and non-metal, strong forces of attraction are chemical bonds formed called ionic bonds. In compounds between metals and non-metals charges on ions always cancel each other out, so compound has no overall charge. |
| Forming molecules | Non-metal atoms bond to each other in different ways, outermost shells of their atom overlap and share electrons. Each pair of shared electrons forms a chemical bond between the atoms these are covalent bonds, no ions are formed. These form molecules. |
| Chemical formulae | The chemical formulae tell us the ratio of each type of ion in a compound. Use ratio as when ions bond together they form structures made of millions of ions. Ratio depends on the charge on each ion. The charges cancel each other out. In covalent molecules can count number of each type of atom in a molecule to get it's formula. |
| Chemical equations | Chemical equations show the reactants and products of a reaction. Can represent this in a word equation ex: hydrogen + oxygen -> water In chemical reaction atoms get rearranged Using symbol equations aids identify amount of substances reacting, better as: - Word equations only useful if language is known - Word equations don't tell us how much of each substance is involved in the reaction. - Word equations can be complicated if large amount of chemicals are involved. Symbol equations are balanced there is the same number of electrons on both sides of the equation, which means total mass of products formed in a reaction is equal to total mass of the reactants. Can check if equation is balanced by counting number of atoms on each side of equation if number is equal then equation is balanced. |
| Making an equation balanced | 1 - Write formula of each reactant and product 2- Decide if equation is balanced 3- Make equation balanced Ex. H2 + 02 -> H202 (not balanced) 2H2 + 02 -> H20 (balanced) |
| Uses of limestone | Limestone rock mainly made of calcium carbonate some types of calcium formed from remains of tiny animals and plants that lived in the sea millions of years ago. Dig limestone from ground in quarries around world use of building material. Many important buildings made of limestone can cut and shape stone taken from ground into block which can be placed on top of each other like bricks in walls. Used limestone in this way to make buildings for hundreds of years. Powdered limestone can be heated with powdered clay to make cement. We mix cement powder with water, sand and crushed rock so small chemical reaction takes place the reaction produces hard, stone-like buidling material - concrete. |
| Heating limestone | Chemical formula for calcium carbonate is CaCO3, made up of calcium and carbonate ions has same number of calcium and carbonate ion in calcium carbonate. When strongly heat limestone strong calcium carbonate breaks down to form calcium oxide, carbon dioxide is also produced in the reaction breaking down a chemical by heating is thermal decomposition. The calcium oxide made is also useful substance in building and farming industries. |
| Rotary lime kiln: To make lots of calcium oxide reaction is done in a furnace called a lime kiln. Fill kiln with crushed limestone and heat it strongly using a supply of hot air. Calcium oxide comes out of the bottom of the kiln, waste gases include carbon dioxide made, which leave the kiln at the top. Calcium oxide is often produced in rotary kiln, where limestone is heated in a rotating drum. Ensures that the limestone is thoroughly mixed with stream of hot air which helps the calcium carbonate to completely decompose. | |
| Reactions of carbonates | Buildings and statues made of limestone badly suffer from damage by acid rain ows to loss of fine features of acid. Limestone is mostly calcium carbonate that reacts with acid a gas is given off in the reaction. |
| Testing for carbon dioxide | Carbon dioxide turns limewater solution cloudy, test works by: - Limewater a solution of calcium hydroxide is alkaline - Carbon dioxide is a weakly acidic gas so reacts with alkaline limewater. - In reaction tiny solid particles of insoluble calcium carbonate are formed as a precipitate Reaction: Calcium hydroxide + carbon dioxide -> calcium carbonate + water - Precipitate of calcium carbonate make limewater turn cloudy as light can no longer pass through solution with tiny bits of white solid suspended in it. Carbonates react with acids to give a salt, water and carbon dioxide for calcium carbonate the reaction with hydrochloric acid is: calcium carbonate + hydrochloric acid -> calcium chloride + water + carbon dioxide |
| Decomposing carbonates | Carbonates decompose, many metal carbonates decompose when heated in a Bunsen flame they form the metal oxide and carbon dioxide. Sodium and potassium carbonate don't decompose at temperature of the Bunsen burner they need a higher temperature. |
| Limestone reaction cycle: Calcium oxide made when we heat limestone strongly the calcium carbonate in limestone undergoes thermal decomposition. When we add water to calcium oxide it reacts to produce calcium hydroxide this gives out heat. Although not very soluble can dissolve little calcium hydroxide in water after filtering this produces a colourless solution called lime water. We can use lime water to test for carbon dioxide. Step 1: Heat calcium carbonate so carbon dioxide given off to produce calcium oxide Step 2: Calcium oxide has a little water added to produce calcium hydroxide Step 3: Calcium hydroxide has more water added and then filtered to produce calcium hydroxide solution Step 4: The lime water has carbon dioxide added to produce calcium carbonate | |
| Neutralising acids | Calcium hydroxide is an alkali it reacts with acids in neutralisation reaction the product of the reaction are a calcium salt and water. Calcium hydroxide is used by farmers to improve soil that is acidic as it is an alkali it will raise the pH of acidic soil. Also used to neutralise acidic waste gases in industry before releasing gases into the air. |
| Development of lime mortar | 6000 years ago Egyptians heated limestone strongly in fire combined with water produced material that hardened with age, used this material to plaster the pyramids. 4000 later Romans mixed calcium hydroxide wit sand and water to produce mortar. Mortar holds other building materials togethers ex. stone blocks or bricks. Works as lime in mortar reacts with carbon dioxide in air producing calcium carbonate again, which means that the bricks or stone block are effectively held together by rock. calcium hydroxide + carbon dioxide -> calcium carbonate + water Amount of sand in mixture is important too little sand and mortar shrinks as dries, too much sand makes it too weak. Even today mortar is used widely as building material though modern mortar made with cement in place of calcium hydroxide can be used in a much wider range of ways than lime mortar. |
| Cement | Though lime mortar holds bricks and stone together very strongly disadvantages are lime mortar doesn't harden quickly, will not set at all where water prevents it from reacting with carbon dioxide. People found that heating limestone with clay in a kiln produced cement much experimenting led to invention of Portland cement. This is manufactured from mixture of limestone, clay and other minerals. They are heated and then grounded up into a fine powder. This type of cement still in used today the mortar used to build modern house is made by mixing Portland cement and sand. This sets when it's thoroughly mixed with water and left for few days. |
| Concrete | Sometimes builders add small stones or crushed rocks called aggregate to mixture of water, cement and sand. When sets it forms a hard, rock-like building material called concrete. Material is very strong is especially good at resisting forces which tend to squash or crush it, can make concrete even stronger by pouring wet mixture around steel rods or bars then allowing it to set. This makes reinforced concrete which is also good at resisting forces that tend to pull it apart. |
| Limestone issues | Limestone is very useful raw material, but mining for limestone can affect the local community and environment. |
| Limestone quarrying | Limestone is quarried from the ground a quarry forms a huge hole in the ground. The limestone is usually blasted from a quarry by explosives then its taken in giant lorries to be processed. Much of the limestone goes to cement factories which are often found near the quarry. Explosive charges used to dislodge limestone from rock face known as blasting. As well as scarring the landscape the blasting noise scares off wildlife and can disturb local resident. Eventually a huge crater is formed these can later be filled with water and can be used as a reservoir or for leisure activities. Also possibility of use as landfill sites for household rubbish before covering with soil and replanting. |
| Development in limestone, cement and concrete | Bathroom tiles traditionally made from ceramics with glazed finished to make them waterproof are very hard wearing. Now more times made from natural stone like travertine these look attractive with each tile having unique markings. Though travertine tiles are porous and can be easily scratched, they must be sealed with a waterproof coating Cement used to make mortar and concrete on building sites before cement mortar was invented builders used lime mortar though this takes much longer to fully set than cement mortar especially in water condition. Restoration of old buildings still needs lime mortar to repair brickwork. Often old buildings have shallow if any foundation their brick walls are much more likely to move than modern buildings with hard cement mortar this results in cracking along weak points in walls. Though lime mortar offers more flexibility and won't crack as easily. Carbon dioxide is a greenhouse gas manufacture of cement contributes about 5% of CO2 gas produced by humans emitted into air. About comes from burning fuels used to heat kilns that decompose limestone. |
| 2. Development in limestone, cement and concrete | Rest come from reaction itself: calcium carbonate -> calcium oxide + carbon dioxide Using lime mortar would contribute less to carbon dioxide emissions as it absorbs carbon dioxide as it sets. Concrete is the world's most widely used building material, concrete was first reinforced using wire mesh to strengthen it, now also use: - glass fibre, carbon fibres, steel rods, poly(propene), nylon, polyesters, Kevlar. Some latest research uses pulp from wood, plants and recycled paper, little recycled paper can improve concrete's resistance to cracking, impact (making it tougher) and scratching. These reinforcing materials are shredded into small pieces before adding them to the concrete mixture. Cheaper to use reinforced concrete to make bridge than from iron or steel though steel is stronger (harder to snap) than concrete. Over long spans suspension bridges use steel's high-tensile strength in cables between concrete towers. Will support the cheap reinforced concrete sections of bridges which cars travel. Short span bridges will always be made reinforced concrete as has low cost. |
| Where metals come from | Found in earth's crust find most metals chemically combined with other chemical elements often with oxygen means metal must be chemically separated from compound before use. A metal ore are rock that have enough metal or metal compound that make it worthwhile to extract. Ores are mined from the ground, some need to be concentated before metal is extracted and purified ex. copper ores ar groun up into power then mixed with water and a chemical makes the copper compound repeal water. Air is then bubbled through the mixture and the copper compound floats on top as froth. The rocky bit sinks and concentrated copper compound is scraped of the top then ready to have copper extracted. Whether worth extracting metals depends on: - how easy it is to extract it from its ore - how much metal the ore contains Can change over time cheaper methods can be discovered also discover new way too extract metal efficiently from rock which contains only small amounts of metal ore. Ore that was once thought as 'low grade' could then become economic source of a metal. |
| Reactivity series | Few metals like gold and silver so unreactive their found in Earth as metals (elements) themselves say they exist in they exist in native state. |
| How do we extract metals | This depends on place on reactivity series a more reactive metal will displace a less reactive metal from its compounds. Carbon (non-metal) will also displace less reactive metals from their oxides. Can use carbon to extract some metals from ores in industry. Can find many metals combined with oxygen - metal oxides, as carbon is more reactive can use carbon to extract metals from oxides. Must heat metal oxides with carbon, carbon removes oxygen from metal oxide to form carbon dioxide metal also formed as element: lead oxide + carbon -> carbon dioxide + lead Removal of oxygen from a compound chemical called reduction. Metals more reactive are extracted by electrolysis. |
| Iron | Iron ore contains iron combined with oxygen in iron oxide. Iron is less reactive than carbon so can extract by using carbon to remove oxygen from iron(III) oxide in the ore, extract iron in blast furnace. Some of iron(III) oxide reacts with carbon, carbon reduces iron(III) oxide forming molten iron and carbon dioxide gas one of reduction reaction taking place a blast furnace: iron(III) oxide + carbon -> iron + carbon dioxide Iron straight from furnace has limited use contains 96% iron and impurities mainly carbon this makes it very brittle although very hard and fairly incomprehensible. When molten can run into moulds and cast into different shapes, this cast iron is used to make wood-burning stoves, man-hole covers on roads and engines. Can treat iron from blast furnace to remove some of the carbon, pure iron is very soft and easily-shaped. However it's too soft for most uses, if to want iron really useful must contain little amounts of other like carbon and metals like nickel. Call mixture with other metals alloys. |
| Steel | Steel is an alloy of iron by adding elements in carefully controlled amounts, can change properties of steel. They aren't one single substance their a mixture there are lots of different types of steels all of them are alloys of iron with carbon and/or other elements. |
| Carbon steels | Simplest steels are carbon steels make these removing most of the carbon from cast iron just leaving small amounts of carbon (0.3% to 1.5%), cheapest to make, use in many products: car body's, knives, machinery, ships, container and structural steel for buildings. Often carbon steels have small amounts of other elements in them as well. High carbon steels with relatively high carbon content is very strong but brittle, low carbon steels is soft and easily shaped - not as strong but less likely to shatter on impact with hard objects. Mild steel one type of low carbon steel contains less than 0.1% very easily pressed into shape which makes it particularly useful in mass production like car bodies |
| Alloy steels | Low-alloy steels are more expensive than carbon steels as they contain 1 to 5% of other metals each of these metals produces a steel well suited to it's purpose. High-alloy steels are more expensive containing a higher percentage of other metals the chromium-nickel steels are known as stainless steels. Used for cutlery and utensils, and to make chemical reaction vessels as combine hardness, strength and resistance to corrosion as don't rust. |
| Properties and uses of aluminium | Silvery shiny metal low density metal so light great conductor of electricity and energy, its malleable and ductile. Even though relatively reactive doesn't easily corrode as aluminium atoms at surface react with oxygen in air, form a thin layer of aluminium oxide which stops any further corrosion. Not a strong metal but can be used to form alloys these alloys are harder more rigid and stronger than pure aluminium. Used for: - drink cans - cooking foil - saucepans - high-voltage electricity cables - aeroplanes and space vehicles - bicycles |
| Extracting aluminium | As is a reactive metal can't use carbon to displace it from its oxide. Instead extract aluminium using electrolysis an electric current is passed through molten aluminium oxide at high temperatures to break it down. First must mine aluminium aluminium ore, contains aluminium oxide mixed with impurities, then the aluminium oxide is separated from the impurities. The oxide must then be melted before electrolysis can take place. Problem using electrolysis to extract metals is a very expensive process, as need to use high temperatures to melt the metal compound. Also need great deal of electricity to extract metal from its molten compound also environmental issues to consider when using so much energy. |
| Properties and uses of titanium | This is a silvery, white metals strong and resistant to corrosion. Like aluminium has an oxide layer on surface that protects it, though denser than aluminium less dense than many other metals. Titanium has very high melting point - 1660 degrees celsius - so can use it for very high temperatures, uses: - bodies of high-performance aircraft and racing bikes (due to combination of strength and relatively low density) - parts of jet engines (keeps strength even at high temperatures) - parts of nuclear reactors (stand up to high temperature and tough oxide layer means resist corrosion) - replacement hip joints (low density, strength and resistance to corrosion) |
| Extracting titanium | Not very reactive so could produce it by displacing it's oxide with carbon, but the carbon makes it brittle. So must use more reactive metal to displace titanium ex. sodium or magnesium. However sodium and magnesium must be extracted by electrolysis themselves in first place. Before displacement of titanium can take place titanium ore must be processed this involves separating the titanium oxide and converting it to chloride. Then chloride is distilled to purify it only then is it ready for the titanium to be displaced by sodium or magnesium. Each of these steps takes time and money. |
| Extracting copper from copper-rich ores | Can extract most copper from copper-rich ores, limited resource and are in danger of running out. Two main methods used to remove copper from the ore: - Use sulfuric acid to produce copper sulfate solution before extracting the copper - Process of smelting (roasting) heat copper ore strongly in furnace with air to produce crude copper. Ex. copper can be found in ore called chalcocite, contains copper(I) sulfide if heat copper (I) sulfide in air it decomposes to give copper metal: copper sulfide + oxygen -> copper + sulfur dioxide Care must be taken in allowing sulfur dioxide into air as gas causes acid rain. So chimneys are fitted with basic 'scrubbers' to neutralise acid rain. Use impure copper as positive electrode in electrolysis cells to make pure copper, about 80% of copper is produced by smelting. Smelting and purifying copper ore use large amounts of heat and electricity and costs money and impact environment. |
| Extracting copper from copper rich ores | Metal ions are positively charged, in electrolysis attracted to negative electrode so metals can be deposited at negative electrode. In industry electrolysis carried out in many cells running at once, method gives pure copper needed to make electrical wiring. Also used to purify impure copper extracted by smelting, in industrial processes electrolysis cells use copper electrodes. Copper can be extracted from copper sulfate solution in industry by adding scrap heap iron more reactive than copper, so displace copper from solution: iron + copper sulfate -> iron sulfate + copper |
| Extracting copper from low-grade ores | Extraction by this process would before be uneconomical but now use bacteria (bioleaching) and plants (phytomining) to help extract copper. Phytomining plants can absorb copper ions from low-grade copper ore as grow, could be on slag heaps previously discarded waste from processing of copper rich-ores then plants are burned and metals can be extracted from ash. Copper ions can be 'leached' dissolved from ash by adding sulfuric acid this makes a solution of copper sulfate. Can use displacement by scrap iron and electrolysis to extract pure copper metal. In bioleaching bacteria feed on low-grade metal ores, by combination of biological and chemical processes can get solution of copper ions called 'leachate' from waste copper ore. Can use scrap iron and electrolysis to extract copper from leachate. 20% of copper comes from bioleaching, likely to increase as sources of copper-rich ores run out. Bioleaching is a slow process so scientists are researching ways to speed it up, presently take years to extract 50% of metal from low grade ores. |
| Exploiting metal ores | Consequences to our environment open cast mining create huge pits that scar the landscape are made creating noise and dust and destroying habitat of plants and animals. Mines leave large heaps of waste. Water i area affected by mining rain drain through exposed ores and slag heaps of waste, groundwater can be acidic. Then ores must be processed to extract metals extract metals ex. sulfide ores are heating strongly in smelting any sulfur dioxide gas that escapes in air is acid rain. |
| Phytomining | As plants grow absorb dissolved ion s in soil through roots some are effedctive at absorbing metal ions, once harvested can extract metals from ash left after burning plats. Can be used in phytomining of low-grad metal ores like copper ores. Copper metal is extracted from plant by dissolving ash in sulfuric acid firs then solution made can be electrolysed to get copper copper collects at negative electrode alternatively scrap iron can be added to solution to displace copper: iron+copper sulfate -> iron sulfate + copper |
| Recycling metals | In UK each person uses around 8kg of aluminum yearly must recycle aluminium saves energy hence money since recycling doesn't involve electrolysis. Comparing recycled aluminum with aluminum extracted from ore 95% energy saving. Also recycle iron and steel 'tin cans' are usually steel cans with thing coating of tin to prevent rusting. Cans are easy to separate from rubbish as they're magnetic. Much of this energy is supplied by burning fossil fuels so recycling helps save dwindling fuel supplies. Copper also recycled but difficult as often alloyed with other metals so would need to be purified for use in electrical wiring. Recycling metals reduces need to mine metal ore and conserves Earth's reserves of metal ores also prevents pollution problems that arise from extracting metal from its ore. |
| Metallic structures | Steel most commonly used metal strength in construction industry needed: - skyscrapers have steel girders supporting them - suspension bridges use thick steel cables - concrete bridges over motorways made from concrete reinforced with steel rods. Drawbacks: - Iron rusts, stainless steel could be used only for small specialist jobs as much more expensive than ordinary steel so protecting steel from rusting costly. Coatings like grease and paint must be regularly reapplied rusting will affect strength of steel and can be dangerous. |
| Some benefits of using metals in construction | Copper good electrical conductor for wiring; unreactive so can be made into water pipes Lead can be easily bent so used to seal joints in roads Steel is strong for gliders and scaffolding Aluminium alloys are corrosion resistant |
| Drawbacks of using metals in construction | Iron and steel can rust severely weakening structures ex. if iron rods used inside reinforced concrete rust, structures can collapse Exploitation of metal ores to extract metals causes pollution and uses up Earth's limited resources Metals are more expensive than other materials like concrete. |
| Fuels from crude oil | Used to run cars, warm homes and make electricity. Oil prices affect us all. Produce crude oil can affect whole world economy by price charge for their oil. |
| Crude oil | Dark smelly liquid mixture of different chemical compounds. Crude oil from ground isn't useful too many substances with different boiling points before can be used must be separated into different substances known as fractions. As properties of substances don't change when mixed can separate by distillation. This separates liquids with different boiling points. |
| Hydrocarbons | Nearly all compounds in crude oil are compounds containing only hydrogen and carbon such compounds are called hydrocarbons. Most of the hydrocarbons in crude oil are alkenes. |
| Alkanes | Most hydrocarbons in crude oil are alkanes the pattern of alkanes is: CnH2n+2 Alkanes described as saturated hydrocarbons as they contain as many hydrogen atoms as possible in each molecule so no more hydrocarbons can be added. |
| Compounds in crude oil | Some hydrocarbon molecules are small with relatively small few carbon atoms in short chains. These short-chain molecules are hydrocarbons that tend to be more useful, they make good fuels as they are very flammable. Other hydrocarbons have lot of carbon atoms and have branches and side branches. The boiling point of a hydrocarbon depends on the size of its molecules. We can use the differences in boiling point to separate the hydrocarbons in crude oil. |
| Short chain molecules of hydrocarbon properties | Low boiling point, high volatility, low viscosity (runny), high flammability |
| Long chain molecules of hydrocarbons properties | High boiling and melting point, low volatility, high viscosity (thick), low flammability with smoky flame. |
| Fractional distillation of crude oil | Separate out hydrocarbons with similar boiling points - fractions. The process is called fractional distillation, each hydrocarbon fraction contains molecules with similar number of carbon atoms. Each of these fractions boils at a different temperature. Which is because of the different sizes of their molecules. Crude oil is near bottom of of fractioning column as hot vapour. The column is very hot at bottom and cooler tending towards the top so the temperature decreases going up the column. The gases condenses when they reach the temperature of their boiling point. So the different fractions are collected as liquids as different levels. Crude oil enters the fractionating column and fractions are collected in a continual process. Hydrocarbons with smallest molecules have lowest boiling points so are collected at the cool top of the column. At the bottom of the column the fractions have high boiling point they cool to form very thick liquids or solids at room temperature. Once collected the fractions need more processing before they can be used. |
| Burning fuels | Lighter fractions of crude oil are useful as fuels, when hydrocarbons burn in plenty of air they release energy, reaction produces carbon dioxide and water. Ex. propane + oxygen -> carbon dioxide + water Carbon and hydrogen in fuel are completely oxidised when they burn like this, 'oxidised' means adding oxygen in a chemical reaction in which oxides are formed. |
| Pollution from fuels | All fossil fuels- oil, natural gas and coal - produce carbon dioxide and water when they burn in plenty air, but also contain other substances, impurities containing sulfur found in fuel causes major problems. All fossil fuels contain sulfur which reacts with oxygen to form a gas - sulfur dioxide, this gas is posinous. As well as acidic this is bad for the environment as it causes acid rain. Sulfur dioxide can also cause engine corrosion. When we burn fuels in car engines even more pollutant can be produced: - When there isn't enough oxygen incomplete combustion occurs instead of carbon dioxide we get carbon monoxide gas (CO) formed. This is a posionous gas your red blood cells pick up this gas and carry it around your blood instead of oxygen. Therefore even small amounts of carbon monoxide can be bad for you. - High temperature inside engine allows nitrogen and oxygen in air to react together, this makes nitrogen oxides. They are poisonous and can trigger some people's asthma. Also they cause acid rain. |
| Pollution from fuels: Particulates | -Diesel engines burn hydrocarbons with bigger molecules than petrol engines, when these big molecules react with oxygen in an engine they don't always completely burn tiny solid particles containing carbon and unburnt hydrocarbons are produced. These particulates get carried into the air, scientists think they may damage cells in our lungs and can even cause cancer. |
| Not Clean fuels | When we burn fuels we produce other substances as well as carbon dioxide and water. Many can affect our health, pollution from cars spreads through atmosphere, the huge increase in our fossil fuels in past 100 years means pollution is real concern. |
| Kinds of pollution | When burn fuel containing carbon attain carbon dioxide, this is the main greenhouse gas in the air. It absorbs energy released as radiation from the surface of the Earth. Most scientists think its causing global warming, this affects temperatures around the world. Another group of pollutants are particulates, which are tiny solid particles made of carbon (soot) and unburnt hydrocarbons. Scientists think these may be especially bad for young children. Particulates may also be bad for the environment as they travel into the upper atmosphere reflecting sunlight back to space causing global dimming. Carbon monoxide is formed when there's not enough oxygen for complete combustion of a fuel. Then the carbon in it is partially oxidised to form carbon monoxide, this is a serious pollutant as it affects the amount of oxygen our blood is able to carry. This is particularly serious for people who have heart problems. |
| Kinds of pollution: Sulfur dioxide and nitrogen oxide | Sulfur dioxide and nitrogen oxides from burning fuels damage us and our environment, in Britain, scientists think the number of people with asthma has increased from air pollution they also form acid rain. These gases dissolve in water droplets in the atmosphere and react with oxygen forming sulfuric and nitric acids. The rain with a low pH can damage plants and animals. |
| Cleaning up our act | Can reduce effects of burning fuels in several ways: ex - remove harmful substances from gases that produced when we burn fuels. For duration of time exhaust systems of cars have been fitted with catalytic converts. Greatly reduces carbon monoxide and nitrogen oxide produced by a car engine. Expensive as contain precious metal catalysts but once warmed very effective. Metal catalysts arranged so have large surface area; causes carbon monoxide and nitrogen oxides in the exhaust gases to react. Produce carbon dioxide and nitrogen: carbon monoxide + nitrogen oxides -> carbon dioxide + nitrogen So increase carbon dioxide levels. Filters can also remove most particulates from modern diesel engines which need to burn off the trapped solid particulates otherwise get blocked. In power stations sulfur dioxide is removed from waste or 'flue' gases by reacting it with calcium oxide or calcium hydroxide - flue gases desulfurisation, the sulfur impurities can also be removed from a fuel before the fuel is burned, happens in petrol and diesel for cars and natural gas and oil in power stations |
| Biofuels | These are fuels made from plant or animal products ex. biodiesel which is made from oils extracted from plants. Can use old cooking oil as biofuel: biogas is generated from animal waste. Biofuels will become more and more important as our crude oil supplies run out. |
| Advantages of biofuels | - They are less harmful to animals and plants than diesel from crude oil, breaks down five times faster than normal diesel - When burn in an engine burns more cleanly reducing particulates emitted it also makes very little sulfur dioxide - As crude oil supplies run out its price will increase and biodiesel will become cheaper to use petrol than diesel - Because crops used to make biodiesel absorb carbon dioxide as they grow in theory biodiesel is carbon neutral. This means carbon dioxide given off when it burns is balanced by the amount absorbed as the plants it is made from when it grows. Hence biodiesel makes little contribution to greenhouse gases in the atmosphere. Though doesn't make zero contribution to carbon dioxide emissions as must account for fuel released when fertilising and harvesting crops, extracting and processing oil and transporting the plant material and biodiesel made. - When biodiesel is made other useful products are made ex. get a solid material that can be used to feed to cattle as high-energy food. Can also get glycerine which can use to make soap. |
| Disadvantages of biofuels | -Use large areas of farmland to produce fuel instead of food could pose problems, if we start to rely on oil-producing crops for our fuel, land once used for food crops will turn to growing biofuel crops. This can result in a famine in poorer countries if price of stable food crops rises as demand overtakes supply. Forests which absorb lots of carbon dioxide might also be cleared to grow the biofuel crops if they get too popular - Worry of the destruction of habitats of endangered species ex. orang-utans are under threat of extinction. Large areas of tropical rainforest where they live are being turned into palm plantations for palm oil used to make biofuel. - At low temperatures biodiesel will start to freeze before traditional biodiesel it turns into a sludge, at high temperatures it an engine it can turn sticky as its molecules join together and can 'gum up' engines. |
| Using ethanol as a biofuel | Can make it by fermenting sugar from sugar beet or sugar cane. In Brazil can grow lots of sugar canes they add the ethanol made to petrol saving money as well as dwindling supplies of crude oil. As with biodiesel the ethanol gives of carbon dioxide when it burns but the sugar cane absorbs CO2 gas during photosynthesis. |
| Hydrogen - fuel for the future | Burns well with clean flame as no carbon in fuel: H2 + 02 -> 2H20 hydrogen + oxygen -> water Water only product from combustion of hydrogen they're no pollutants made when hydrogen burns and no extra carbon dioxide is added to the air. Also water is potentially a huge natural source of hydrogen. The hydrogen can only be obtained by electrolysis but electricity must be supplied from a sustainable source if want to conserve fossil fuels and control carbon dioxide emissions. Problems are when mixed with air it is explosive so they aresafety concerns in case of leaks or accidents in vehicles powered by hydrogen. Vehicles normally run on liquid fuels but hydrogen is a gas therefore takes larger volume so storage is a problem. We can use high-pressure cylinders but these also have safety concerns in crashes. |
| Cracking hydrocarbons | We can break down large hydrocarbon molecules in the process of cracking as these large molecules aren't useful as fuels as they are difficult to vaporise. This takes place at an oil refinery in a steel vessel called a cracker. In the cracker a heavy fraction produced from crude oil is heated to vaporise the hydrocarbons, the vapour is then passed over a hot catalyst or mixed with steam. It is heated to a high temperature the hydrocarbons are cracked as a thermal decomposition reaction takes place. The large molecules split apart to from smaller, more useful ones. |
| Example of cracking | Decan a medium-sized molecule with ten carbon atoms when heated to 500 degrees celsius with a catalyst it breaks down. One of the molecules produced is pentane which is used in petrol. Also get propene and ethene which can use to produce other chemicals. C10H22 -> C5H12 + C3H6 + C2H4 It a thermal decomposition, the cracking process produces different types f molecules. One of which is pentane pent tells us it has five carbon atoms, and ane tells us it's an alkane so is a saturated hydrocarbon. The -ene in ethene tells us it's an alkene so they molecules are unsaturated as they contain a double bond between two of their carbon atoms. The general formula is CnH2n |
| Akene test | Alkenes burn they also react with bromine (orange) with the products being colourless. This means we have good test to see if a hydrocarbon is unsaturated: Positive test: unsaturated hydrocarbon + bromine water (orange - yellow) -> products (colourless) Negative test: saturated hydrocarbon + bromine water (orange) -> no reaction (orange) |
| Making polymers from alkenes | Fractional distillation of crude oil and cracking produces a range of hydrocarbons these are very important to our way of life. Oil products are all around us, hydrocarbons are our main fuels use them in transport to cook and for heating. Also use them to make electricity in oil-fired power stations. Chemicals from crude oil are used to make things ranging from cosmetics to explosives - one of most important ways we use chemicals from oil is to make plastics. |
| Plastics | These are made up of huge molecules made from lots of small molecules joined together the small molecules are monomers the huge molecules are polymers. We make different types of plastics which have different properties using different monomers. Ethene is the smallest unsaturated hydrocarbon molecule we can turn it into a polymer known as poly(ethene) or polythene. Poly(ethene) is useful a really useful plastic as it is easy to shape, strong and transparent unless colouring is added. Plastic bags, plastic drink bottles and clingfilm ex. of poly(ethene) Propene used to make polymer called poly(propene) it forms a strong tough plastic use to make things - carpets, milk crates and ropes |
| How monomers join together | When alkene molecules join together the double bond between carbon atoms in each molecule 'opens up'. It's replaced by single bonds as thousands of molecules join together the reaction is polymerisation. One diagram n is a large number. |
| New and useful polymers | Polymers with special properties to do particular jobs medicine an area new polymer materials will eventually take over from filling for teeth that contain mercury which is potential hazard to dental workers. Other developments: - new softer linings for dentures (false teeth) - new packaging material - implants that can slowly release drugs into a patients |
| Light-sensitive plasters | For some taking of plaster very painful for both old and young have fragile skin, chemists made a plaster where the stickiness can be switched off before plaster is removed, the plater uses a light-sensitive polymer. Plaster is put normally, to remove the plaster the top layer is peeled away from the lower layer which stay stuck to skin, once lower layer is exposed to light, the adhesives becomes less sticky making it easy to peel of skin. |
| Hydrogels | These a polymer chains with few cross-linking units between chains this makes a matrix that can trap water. These hydrogels are used as wound dressing they allow the body to heal in moist, sterile conditions. Which makes them useful for treating burns. Latest 'soft' contact lenses are also made from hydrogels to change the properties of hydrogels scientist can vary the amount of water in their matrix structure. |
| Shape memory polymers | New polymers also act as stitches, new shape memory polymer being developed by doctors which will make stitches that keep sides of cut together. When shape memory polymer is used to stitch a wound loosely the temperature of the body makes the thread tighten and close the wound, apply right force. This is an example of smart polymer ex. one that changes in response to changes around it. In this case a change in temp causes polymer to change shape. Later when wound healed polymer designed to dissolve and is harmlessly absorbed by the body. So there will be no need to go back to the doctor to have stitches out. |
| New uses for old polymers | Bottles buy fizzy drinks ex. of using plastic because of properties. Bottles are made from plastic called PET. Polymer is made from is ideal for making drinks bottles. It produces a plastic that's strong and tough and which can be made transparent. The bottles made from this plastic are much lighter than glass bottles which means that they cost less to transport and easier for us to carry around. The PET from recycled bottles is used to make polyester fibres for clothing like fleece jackets and the fillings for duvet covers. School uniform and football shirts are now also made from recycled drink bottles. |
| Plastic waste | Waste when finished use rubbish in streets, on beaches, wildlife trapped in waste or eat plastics and die. Most plastic packaging ends up in rubbish in landfill tips other rubbish in tips rots away quickly, microorganisms in soil break it down. Many wast plastics last hundreds of years before broken down completely so take up space in landfill site. What was useful property during working life of plastic (lack of reactivity) becomes a disadvantage in a landfill site. |
| Biodegradable plastics | Scientists working to solve problems of plastic waste now making more plastics that rot away in soil when we dump them known as biodegradable. Can be broken down by microorganisms, scientists found different ways to speed up decomposition one way uses granules of cornstarch built into the plastic. The microorganisms in soil feed on the starch this breaks the plastic up into small pieces more quickly. Other types of plastic been developed that are made from plant products, plastic called PLA, poly(lactic acid) can be made from cornstarch the plastic is totally biodegradable and is used in food packaging though it can't be put in a microwave which limits it sue in ready meal packaging. Can also make plastic carrier bags using PLA in carrier bags the PLA is mixed with a traditional plastic this makes sure the bag is strong enough but will still biodegrade a lot more quickly. Using plastics like PLA helps preserve our supplies of crude oil, remember that crude oil is the raw material for many tradition plastics like poly(ethene). |
| Recycling plastics | Some plastics can be recycled once sorted into different types they can be melted won and made into new products this can save energy and resources. Though recycling plastics does tend to be more difficult than recycling other things like metal the plastic waste takes up lots of space so is awkward to transport. Sorting out plastics into different types adds another tricky step to process. The energy savings are less than we get with other recycled materials. Would help recyclers if they could collect the plastics already sorted. You might have seen recycling symbols on some plastic products. |
| Ethanol | This is amember of the group of organic compounds called the alcohols formula is C2H6O which is often written as C2H5OH. This shows the -OH group that all alcohols have in their molecules. |
| Making ethanol by fermentation | Ethanol found in alcoholic drinks ethanol for drinks is made by fermentation of sugar from plants. Enzymes in yeast break down the sugar into ethanol and carbon dioxide gas: sugar (glucose) -> ethanol + carbon dioxide Ethanol is also used as a solvent methylated spirit is mainly ethanol. Decorators can use it to clean brushes after using oil-based paints it's also used to make perfume. We have already seen how ethanol can be used as a fuel it can be mixed with petrol or used by itself to run cars. |
| Making ethanol from ethene (hydration) | Ethanol for industrial use as a fuel or solvent can be made from ethene gas instead of by fermentation. Ethene is made when oil companies crack hydrocarbons to make fuels. Ethene is the main by-product made in cracking, ethene gas can react with steam to make ethanol. ethene + steam -(catalyst)-> ethanol reaction is called hydration, it requires energy to heat the gases and to generate a high pressure. The reaction is reversible so ethanol can bread down into ethene and steam. So unreacted ethene and steam need to recycled over the catalyst. This process is continuous and produces no wast products - these are advantages when making products in industry. When ethanol is made industrially by fermentation the process is carried out in large vats which have to be left. This called a batch process which takes longer than a continuous process. Carbon dioxide a greenhouse gase is also given off in fermentation. |
| Disadvantages of hydration | However using ethene to make ethanol relies on crude oil which is a non-renewable resource. Therefore making ethanol as a biofuel by fermenting sugars from plant material ( a renewable resource ) will become ever more important. The sugars are from crops like sugar can or sugar beet any cereal crop can also be used as the raw material. These need their starch to be broken down to sugars before fermentation takes place. Although we have seen before there are issues that need to be addressed when using crops for large-scale industrial processes. |
| Extracting vegetable oil | Plants use Suns energy to produce glucose from carbon dioxide and water during photosynthesis: carbon dioxide + water -(chlorophyll energy from sunlight-> glucose + oxygen Plants then turn glucose into other chemicals using more chemical reaction in some cases these other chemicals can be useful to us ex. vegetable oils from plants - oilseed rape, make biofuels and foodstuffs. Find these oils in seeds of the rape plant. Farmers collect the seeds from the plants using a combine harvester the seeds are then taken to a factory where they are crushed and pressed to extract their oil. Impurities are removed from the oil, then processed to make it into useful products. Extract other vegetable oils using steam ex. can extract lavender oil from lavender plants by distillation. The plants are put into water and boiled, the oil and water evaporate together and are collected by condensing them. The water and other impurities are removed to give pure lavender oil. |
| Vegetable oils as foods and fuels | Vegetable oils are important foods provide important nutrients ex. olive oil is source of vitamin E. Also contain great deal of energy which makes them useful foods and sources of biofuels like biodiesel. There are lots of different vegetable oils each vegetable oil contains mixtures of compounds with slightly different molecules. Although all vegetable oils have molecules which contain chains of carbon atoms with hydrogen atoms: In some vegetable oils the hydrocarbon chains contain carbon-carbon double bonds (C=C). Call these unsaturated oils, can detect the double bonds in unsaturated oils with bromine water. unsaturated oil + bromine water (orange) -> colourless solution |
| Cooking with vegetable oils | When cook food heat it to a temperature where chemical reactions cause permanent changes to happen to food. Cooking food in vegetable oil gives different results that cooking water which is because boiling points of vegetable oils is higher than that of water. hence vegetable oils can be used at higher temperature than boiling water. |
| What's the differnece | When we cooking using vegetable oil: -food cooks more quickly -often the outside of food turns a different colour and becomes crispier -the inside of the food should be softer if you don't cook it so long Cooking food in oil means that food absorbs some of the oil which contains lots of energy this can make the energy content of fried food much higher than that of same food cooked by boiling it in water. One reason why regularly eating too much fried food is unhealthy. |
| Hardening unsaturated vegetable oil | Unsaturated vegetable oils are usually liquids at room temperature. The boiling and melting points of these oils can be increased by adding hydrogen to the molecules. The reaction replaces some or all of the C=C double bonds with C-C single bonds. With this higher melting point the liquid oil becomes a solid at room temperature we call changing a vegetable oil in this way hardening it. Harden vegetable oil by reacting it with hydrogen gas to make the reaction happen we must use a nickel catalyst and carry it out at about 60 degrees celsius. Oils that have been treated like this are called hydrogenated oils. They are solids at room temperature this means that they can be made into spreads to be put on bread can use them to make cakes, biscuits and pastry. |
| Emulsions in foods | Texture of food important part of foods some smooth foods made from a mixture of oil and water - don't mix. When mixed together by making oil into small droplets spread out throughout the water and produce mixture called an emulsion ex. milk (small droplets of animal fat dispersed in water). Emulsions often behave differently to things we make them from ex. mayonnaise made from ingredients including oil and water though is vicious. Important ingredient in mayonnaise is egg yolks add yellow colour and stop oil and water from separating into layers. Food scientists call type of substance an emulsifier. Emulsifiers ensure oil and water in an emulsion can't separate out which means the emulsion stays thick and smooth. Any cream sauce needs an emulsifier, without it would separate. Popular emulsion: ice cream made from vegetable oils, luxury ice cream may also use animal fats. Emulsifiers keep oil and water mixed together in ice cream while freeze it, without it water in ice cream freezes separately producing crystals of ice. Ice cream would be crunchy not smooth happens if melt + freeze. |
| Other uses of emulsions | Emulsifiers also important in cosmetics industry: face creams, body lotions and lip gloss are all emulsions. Emulsion paint is water-based paint with oil droplets dispersed throughout its commonly used for painting indoor surfaces like plastered walls. |
| How an emulsifier works | Emulsifier is a molecules with a tail attracted to oil and head that is attracted to water. The tail is a long hydrocarbon chain this is called the hydrophobic part of the emulsifier molecule. The head is a group of atoms that carry a charge. This is called the hydrophilic part of the molecules. The tails dissolve in oil making tiny droplets. The surface of each oil droplet is charged by the heads sticking out into the water as like charges repel the oil droplets repel each other. This keeps them spread throughout the water stopping he oil and water separating out into two layers. |
| Emulsifying additives | Use substances to make food look or taste better call a substance that's added to preserve it or improve its taste, texture or appearance a food additive. Additives that have been approved for use in Europe are given E numbers these can be used to identify them. Each group of additives given range of E numbers these tell us what kind of additive it is emulsifiers are usually given E numbers in range 400 to 500 along with stabilisers and thickeners. E440 is example - pectin. As emulsifiers top oil and water separating out into layers they make it less obvious that foods are rich in oil or fat ex. Chocolate. The cocoa butter which has a high energy content usually mixed in well often with emulsifiers. though when goes out of date fatty butter (white haze) starts to separate out. Emulsifiers make oil and fat more edible in foods they can make a mixture that is creamier and thicker in texture than either oil or water this makes it easier and more tempting for us to eat too much fatty food. |
| Vegetable oils in our diet | Scientists have found that eating vegetable oils instead of animal fats can have positive effect on heatlth of heart. The saturated fats find in things like butter and cheese can make blood vessels in heart become clogged up. Though unsaturated fats in vegetable oils good for you they are a source of nutrients like vitamin E. They also help to keep arteries clear and reduce chance of you having heart disease. The levels of specail fat called cholesterol in blood give doctors idea bout risk of heart disease. People who eat vegetable oils rather than animal fats tend to have lower level of 'bad' cholesterol in their blood. Fatss used to cook chips and other fast foods often contain certain fats that aren't good for us. Scientis are concerned that eating these fats may have caused inrease in heart disease. Changes in food labelling very important but many products - fast foods, often contain high levels of potentially harmful fats from the oil they were cooked in. Yet these are exempt from labelling reguulation and may be advertised as cholesterol frre and cooked in vegetable oil. |
| Structure of Earth | Earth diameter is about 12800km. Earth is made up of layers that formed millions of years ago early in the history of our planet. Heavy materials sank towards the centre of the Earth while lighter material floated on top. This produced a structure consisting of a dense core, surrounded by mantle outside the mantle there is a thin outer layer called the crust. Above the Earth's crust we have a thin layer of gases called the atmosphere. Earth's crust is a very thin layer compared to the diameter of the Earth, thickness can vary from as thin as 5km under the oceans to 70km under the continents. Underneath the crust is the mantle this layer is much thicker than the crust is nearly 3000km thick. The mantle behaves like a solid but it can flow in parts slowly. Finally inside the mantle lies the Earth's core this is about half the radius of the Earth it's made of a mixture of the magnetic metals, nickel and iron. The core is actually two layers the outer core is a liquid while the inner core is solid. |
| Layers of Earth: | Atmosphere: About 80% of air in atmosphere lies within 10 km of the surface. Crust: The average thickness of the crus is about 6km under the oceans; about 35 km under continental areas Mantle: Starts underneath crust and continues to about 3000 km below Earth's surface. BEhaves like solid but is able to flow slowly. Core: Radius of about 3500 km, made of nickel and iron outer core is liquid, inner core is solid. All minerals and other resources we depend on in our lives come from thin crust of Earth, oceans and atmosphere. We get all the natural materials we use plus the raw materials for synthetic and processed materials from these sources. There is limited supply or available resources to us so should take care to conserve them for future generations. |
| Developing scientific ideas from evidence | Know about structure inside Earth from evidence from earthquakes following earthquake seismic waves travel through the Earth. Waves are affected by different layers in Earth's structure. By observing how seismic waves travel, scientists have built up our picture of inside of Earth. Also by making careful measurments physicist have been able to measure the mass of the Earth and calculate its density. The density of the Earth as a whole is much greater than the density of rocks found in crust which suggest that the centre of the EArth must be made from a different material to the crust. This material must have a much grater density than the material in the crust. |
| Continents are moving | Continents seem to fit together the fossils and rock structures that we find when we look are similar also rocks on two continents have been built up in the same sequence. Scientists think that two continents were once joined together as one land mass. |
| Tectonic plates | Of course continents moved apart slowly in fact still moving today at rate of few centimetres each year. They move because the Earth's crust and uppermost part of the mantle is cracked into a number of huge pieces called tectonic plates. Deep within Earth radioactive atoms decay producing vast amounts of energy this heats up molten mineral in the mantle which expand they become less dense and rise towards the surface. Cooler material sinks to take their place forces created by these convection currents move the teconic plates slowly over he surface of the Earth. Where the boundaries of plates meet huge stresses build up. These forces make the plates buckle and deform and mountains may be formed. These plates may also suddenly slip past each other these sudden movements cause earthquakes. However its difficult for scientists to know exactly where and when the plates will suddenly slip like this. |
| Trying to predict the unpredictable :( Such a bad title= | Earthquakes and volcanic eruptions can be devastating but making accurate predictions of when they will take place is difficult. Markers placed across a plate boundary or across the crater of a volcano can be monitored for movement. Scientist also monitor the angels of the slopes on volcanoes. The sides of some volcanoes start to bulge outwards before an eruption any abnormal readings can be used as a warning sign. Has also been found that rocks heat up before earthquakes as result of extreme compression so satellites with infrared cameras can monitor the Earth's surface for unexpected rises in temperature. Our ability to predict these natural events and evacuate people at risk will improve advances made by scientists. |
| Wegner's revolutionary theory Who makes these titles? | In past scientists thought features like mountain ranges caused by crust shrinking as early molten EArth cooled down. Idea that huge land masses once existed before the continents we know today was put forward in the late 19th century by the geologist Edward Suess. Though that a huge southern continent had sunk he suggested that this left behind a land bridge between Africa and South America. The idea of continental drift was put forward first by Alfred Wegener in 1915, though fellow scientists found Wegener's ideas hard to accept mainly becauses he could not explain how the continents had moved. Theory was finally shown to be right 50 yrs later. Scientists found seafloor is spreading apart in some places, where molten rock is spewing out between two continents this led to new theory of plate tectonics. |
| Earth's atmosphere in past | Earth was formed about 4.5 billion year ago to begin with was molten ball of rock and minerals for its first billion years it was a violent place. The Earth's surface was covered with volcanoes belching fire and gases into the atmosphere. |
| Earth's early atmosphere | These are several theories about Earth's early atmosphere one suggest that volcanoes release carbon dioxide, water vapour and nitrogen gas and these gases formed early atmosphere condensed as the Earth gradually cooled down and fell as rain. Water collects in hollows in the crust as the rock solidified and first oceans were formed. As EARth began to stabilise the atmosphere was probably mainly carbon dioxide. These could have been some water vapour and traces of methane and ammonia. There would have been very little or no oxygen at this time. Some scientist believe nitrogen was another gas present at this time. This is very like the atmospheres which we know exist today on planets Mars and Venus. After initial violent years of history of the Earth, the atmosphere remained quite stable until life first appeared on Earth. |
| Oxygen in the atmosphere | Scientists think life on Earth began about 3.4 billion years ago - when simple organisms similar to bacteria appeared. These could make food for themselves using the breakdown of other chemicals as a source of energy. Later, bacteria and other simple organisms like algae evolve they could use the energy from the Sun to make their own food by photosynthesis this produced oxygen gas as a waste product. By two billion years ago the levels of oxygen were rising steadily as algae and bacteria thrived in the sea. More and more plants evolved all of them were photosynthesising removing carbon ioxide and producing oxygen. As plants evolved they successfully colonise most of the surface of the Earth so the atmosphere became richer and richer in oxygen this made it possible for animals to evolve. These animals couldn't make their own food and needed oxygen to respire. On other hand many of earliest living microorganisms couldn't tolerate a high oxygen concentration so they largely died out as there were fewer places where they could live. |
| Life on Earth | Oxygen in our atmosphere explained by photosynthesis in plants, the plants probably evolved from simple organisms like lankton and algae in the ancient oceans. |
| Miller-Urey experiment | Know type of molecules that make up living things to make these need compounds - amino acids these make proteins. Most amino acids contain element hydrogen, nitrogen and oxygen. So could re - create condition in the early atmosphere in an experiment. Should amino acids have been made in those conditions? That's the question the scientist Miller and Urey tried to answer in 1952. used a mixture of water, ammonia and methane to model the early atmosphere. Under normal conditions these gases don't react together through Miller and Urey used a high voltage to produce a spark to provide the energy needed for a reaction. This stimulated lightning in a storm the experiment ran for a week then they analysed the mixture formed it looked like a brown soup in it they found 11 different amino acids. |
| Miller-Urey experiment continued | This experiment provided evidence that it was possible to make the molecules from gases that may have been in early atmosphere. Miller and Urey published findings in 1953 they froze some of the mixtures formed into their experiments and stored it. In 2008 other scientists analysed it using modern techniques. They found 22 amino acids as well as other molecules important for life. Theories of the composition of the early atmosphere have changed since the 1950s ex. many people think the atmosphere was mainly carbon dioxide and nitrogen before the first life on Earth. Though when they carry out similar experiments to Miller and Urey they still get similar biological molecules made. They are opponents of the theory that biological material can be made from non-biological material. They argue that Miller- Urey experiment only works in the absence of oxygen. Believe that oxygen would have been present before the generally accepted time for its appearance this would make and conclusions based on Miller-Urey or similar experimental results invalid. |
| Other theories | Another theory based on analysis of meteors that crash to Earth from space in 1969 a meteorite fell from the sky above Australis known as the Murchison meteorite mass over 100kg. Though most interesting were the range of organic molecules found in it. Latest studies of fragments of meteorites identified about 70 differnt amino acis. This shows that the molecules capapble of starting life on Earth may have arrived from outer space. Another source of biological molecules could have beeen deep under the oceans. Near to volcanic vents on seabed get conditions and chemicals needed. |
| Life That's a good title ;) | However even though the 'building blocks' of life might have been on Earth doesn't explain the really difficult step of how they go on to form life. The organic molecules could have formed a primordial soup all the molecules needed to start life could have been in the seas then they would have had to react together to somehow make the first primitive cells. Protein molecules capable of replicating themselves might have been involved at this stage. Others think that simple living organisms could have arrived on Earth in meteorites or comets. Their evolution had started elsewhere this extraterrestrial seeding from outer space supports the theory of life in other parts of the universe. Of course nobody knows for sure but the search for evidence goes on. |
| Carbon 'locked into' rock | Carbon dioxide is taken up by plants during photosynthesis. The carbon can end up in a new plant material Then animals eat the plants and the carbon is transferred to the animals tissues - bones, teeth and shells. Over millions of years dead bodies of huge numbers of these living organisms built up at bottom of vast oceans eventually they formed sedimentary carbonate rocks like limestone. Some of these living things were crushed by movements of the Earth and heated within the crust. They formed the fossil fuels coal, crude oil and natural gas. In this wa much of carbon from carbon dioxide in the ancient atmosphere became locked up within the Earth's crust. Carbon dioxide also dissolved in oceans it reacted to make insoluble carbonate compounds. These fell to the seabed and helped to form carbonate rocks. |
| Ammonia and methane | At the same time the ammonia and methane from the Earth's early atmosphere reacted with oxygen formed by the plants. This got rid of methane and ammonia the nitrogen levels in the atmosphere built up as this a unreactive gas. |
| The atmosphere today | By 200 million years ago the proportions of gases in the Earth's atmosphere had stabilised. These were much the same as today with 21 oxygen and 78% nitrogen. |
| Separating the gases in air | IN industry gases separated by the fraction distillation of liquid air. This is a process in which liquids with different boiling points are separated. So first we have to ge air cole enough for it to condense into a liquid it has to be cooled to a temperature below -200 degrees celsius. In industry they do this by compressing the air to about 150 atm which warms the air up so its cooled down to normal temperatures by passing air over pipes carrying cold water. The main cooling occurs when the pressure is released as this happens the air is allowed to rapidly expand whis is similar to what happens in an aerosol can when pressure is released as the aerosol is sprayed. The temperature drops far enough for the gases in air to condense to liquids, the carbon and water can be removed from the mixture as they are solids at this low temperature. The liquid is then allowed to warm up and at -196 degrees celsius nitrogen boils off first it is collected from the top of a tall fractioning column |
| Nitrogen uses | Used to cool things down to low temperatures at these temperatures most things solidify used to store sperm in hospitals to help in fertility treatment. Nitrogen gas is unreactive so use it in sealed food packaging to stop food going off. Also used in oil tankers when the oil is pumped ashore to reduce the risk of explosion. In industry nitrogen gas is used to make ammonia which we convert into fertilizers. |
| Oxygen uses | Used to help people breathe often at accident scene or in hospital also used to help things react ex. - high temperature welding and in steel-making process. |
| Carbon dioxide in the atmosphere | Over past 200 million yrs levels of carbon dioxide haven't changed much due to the natural cycle of carbon in which carbon moves between the oceans, rock and atmosphere. Left to itself the cycle is self-regulating the oceans act as massive reservoirs of carbon dioxide they absorb excess carbon dioxide when it's produced and release it when it is in short supply. Plants also remove carbon dioxide from the atmosphere, often call plants and oceans carbon dioxide 'sinks'. |
| The changing balance | Over recent past have greatly increased amount of carbon dioxide released into the atmosphere we burn fossil fuels to make electricity, heat homes and run cars has enormously increased the amount of carbon dioxide we produce. No doubt that levels of carbon dioxide in the atmosphere are increasing. Can record annual changes in the levels of carbon dioxide which are due to seasonal differences in the plants the variation s within each year show how important plants are for removing CO2 from the atmosphere but the overall trend over the recent past has been ever upwards. Balance between carbon dioxide produced and carbon dioxide absorbed by CO2 sinks is very important. |
| Changes | When burn fossil fuels carbon has been locked up for hundreds of millions of year in the fossil fuels is released as carbon dioxide into the atmosphere when used as fuel ex. propane + oxygen -> carbon dioxide + water As carbon dioxide levels in the atmosphere go up the reactions of carbon dioxide in sea water also increase the reactions make insoluble carbonates these are deposited as sediment on the bottom of the ocean they also produce soluble hydrogen carbonates mainly of calcium and magnesium. These compounds simply remain dissolved in the sea water. In this way the seas and oceans acts a s a buffer absorbing excess carbon dioxide ut releasing it if necessary however there are now signs that the seas cannot cope with all the additional carbon dioxide that we are currently producing ex. coral reefs are dying in the more acidic conditions caused by excess dissolved carbon dioxide. |
| Thinking of solution at what cost? Seriously these titles | Most of electricity use in UK is made by burning fossil fuels this releases carbon dioxide into the atmosphere. Scientists have come up with number of solution one solution would be to pump carbon dioxide produced in fossil fuel power station dep underground to be absorbed into porous rocks this is called carbon capture and storage. It's estimated that this would increase the cost of producing electricity by about 10%. This is emotional Obs, you just finished chemistry! |
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