Chemistry review c10 c14


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Chemistry review c10 c14

  1. 1. Mary Rodriguez CHEMISTRY REVIEW C10-C14
  2. 2. METALS
  3. 3. • 1 Distinguish between metals and nonmetals by their general physical and chemical properties. • 3 Explain why metals are often used in the form of alloys. • 2 Identify and interpret diagrams that represent the structure of an alloy. 10.1 PROPERTIES OF METALS
  4. 4. Metals Often have 1-3 outer valence electrons Lose valence electrons quite easily. Form oxides that are basic Good reducing agents NonMetals Often have 4-8 valence electrons Gain or share valence electrons easily. Good oxidizing agents Form oxides that are acidic CHEMICAL DIFFERENCES
  5. 5. Metals Good electrical conductors Good heat conductors Malleable – Can be beaten into thin sheets Ductile – Is able to be stretched into wire. Mostly solid at room temperature Non-metals Poor conductor of electricity Poor conductor of heat Nonductile Solids, liquids or gases at room temperature PHYSICAL PROPERTIES
  6. 6. the mixture of two or more metallic elements. two different types of atoms incoherently mixed together, without any apparent order. (In GCSE, if you see this, you can almost assume that the diagram is suggesting an alloy.) ALLOYS
  7. 7. What makes alloys special is that since the atoms are all jumbled together of different sizes, it is much more difficult for alloy layers to slide over each other, so alloys are harder than pure metals. An alloy has the properties of both metals, therefore it is beneficial when two metals can mix to negate the weaknesses of each other ALLOYS
  8. 8. Metals such as Copper or iron are too soft for many uses. Therefore, these metals are often mixed with other methods to acquire make it harder. Additionally, an alloy has the properties of both metals, therefore it is beneficial when two metals can mix to negate the weaknesses of each other. Brass is used in electrical fittings, 70% copper and 30% zinc. Bronze is used for bearings and bells, and it often composed composed of 80% copper and 20% Tin. Duralumin is used for airplane manufacture, 96 % aluminium and 4% copper and other metals. EXAMPLES
  10. 10. This strong bonding generally results in dense, strong materials with high melting and boiling points. Usually a relatively large amount of energy is needed to melt or boil metals. Good conductors of electricity/heat because these 'free' electrons carry the charge of an electric current when a potential difference (voltage!) is applied across a piece of metal. The 'hot' high kinetic energy electrons move around freely to transfer the particle kinetic energy more efficiently to 'cooler' atoms. Typically - silvery surface (tarnished by corrosive oxidation in air and water. Metals are very malleable (readily bent, pressed or hammered into shape.) The layers of atoms can slide over each other without fracturing the structure When planes of metal atoms are 'bent' or slide the electrons can run in between the atoms and maintain a strong bonding situation PROPERTIES OF METALS
  11. 11. The crystal lattice of metals consists of ions (NOT atoms) surrounded by a 'sea of electrons' forming another type of giant lattice. The outer electrons (-) from the original metal atoms are free to move around between the positive metal ions formed (+). These free or 'delocalised' electrons are the 'electronic glue' holding the particles together. There is a strong electrical force of attraction between these free and mobile electrons (-) and the 'immobile' positive metal ions (+) and this is the metallic bond. Metallic bonding is not directional – there is an attractive force between the mobile electrons that act in every direction about the fixed (immobile) metal ions. Metals can become weakened when repeatedly stressed and strained ('metal fatigue' or 'stress fractures'. ) It is important develop alloys which are well designed, well tested and will last the expected lifetime of the structure whether it be part of an aircraft (eg titanium aircraft frame) or a part of a bridge (eg steel suspension cables). METAL BONDING
  12. 12. • 1 Place in order of reactivity: potassium, sodium, calcium, magnesium, zinc, iron, hydrogen and copper, by reference to the reactions, if any, of the elements with water or steam, dilute hydrochloric acid (except for alkali metals). • 2 Compare the reactivity series to the tendency of a metal to form its positive ion, illustrated by its reaction, if any, with: the aqueous ions of other listed metals, the oxides of the other listed metals. • 3 Deduce an order of reactivity from a given set of experimental results. 10.2 REACTIVITY SERIES
  13. 13. REACTIVITY SERIES Metal Reactivity Extraction Potassium Reacts with water Electrolysis Sodium Calcium Magnesium Reacts with acids Zinc Smelting with coke (Blast Furnace)Iron Hydrogen Included for comparison Copper May react with strongly oxidizing acids Heat or physical extraction
  14. 14. THE TENDENCY OF A METAL TO FORM ITS POSITIVE ION • Elements at the top form positive ions the easiest, and this tendency decreases as you go down the group. Valence electrons are more easily lost up in the reactive series to form ionic bonds. • Reaction of Potassium with Water 2K (s) + 2H2O (l) —-> 2KOH (aq) + H2 (g) Potassium + Water —-> Potassium Hydroxide + Hydrogen • Reaction of Magnesium with Water 2Mg (s) + 2H2O —> 2Mg(OH)2 (aq) + H2 Magnesium + Water —> Magnesium Hydroxide + Hydrogen • Reaction of Magnesium with Steam Magnesium + Steam —> Magnesium Oxide + Hydrogen
  15. 15. • Let’s take three unknown metals X,Y and Z • We will put these three metals in three separate beakers immersed with Hydrochloric Acid • Observe • In the exam, you are likely to see these type of questions. • The beaker which produces the most bubbles, effervescence is likely to contain the most reactive metal. • However, for this to be a successful experiment, we have to ensure some variables are controlled. We call this controlled variables. Time allowed for reaction to occur. Temperature of acid Initial surface of metal Volume of acid Many more. EXPERIMENTAL RESULTS
  16. 16. • 1 Describe the use of carbon in the extraction of some metals from their ores. • 2 Describe the essential reactions in the extraction of iron in the blast furnace. • 3 Relate the method of extraction of a metal from its ore to its position in the reactivity series. 10.3 EXTRACTION OF METALS
  17. 17. Carbon is oxidised to Carbon Dioxide Coke, which consists mostly of carbon, is burned to give off heat. CARBON IN EXTRACTION OF METALS
  18. 18. BLAST FURNACE 1. Hot blast from Cowper stoves 2. Melting zone 3. Reduction zone of ferrous oxide 4. Reduction zone of ferric oxide 5. Pre-heating zone 6. Feed of ore, limestone and coke 7. Exhaust gases 8. Column of ore, coke and limestone 9. Removal of slag 10. Tapping of molten pig iron 11. Collection of waste gases
  19. 19. • Iron Ore: The major component of iron is hematite, which is mainly composed of Iron (III) oxide, mixed with some sand and other compounds • Limestone: Mainly composed of Calcium Carbonate, CaCO3 • Coke: Mainly made from coal, and it is composed nearly out of pure carbon. INSIDE BLAST FURNACE
  20. 20. • Stage 1: The coke is burned, which gives off heat. The hot air starts burning the coke and allows it to react the oxygen in the air to produce Carbon Dioxide Carbon + Oxygen → Carbon Dioxide C (s) + O2 (g) → CO2 (g) • Stage 2: Carbon Monoxide is made The Carbon Dioxide subsequently reacts with more coke: Carbon + Carbon Dioxide → Carbon Monoxide C(s) + CO2 →2CO (g) • Stage 3: Iron Oxide (III) is reduced. Only in this step does extraction actually occur. The Carbon Monoxide reacts with the iron ore, producing liquid iron, something we actually want. Iron (III) oxide + Carbon Monoxide → Iron + Carbon Dioxide Fe2O3 (s) + 3CO (g) → 2Fe (l) + 3CO2 (g) STAGES
  21. 21. • The limestone breaks down in the heat of the furnace • CaCO3 → CaO + CO2 • Calcium Carbonate → Calcium Oxide + Carbon Dioxide • The calcium oxide that is formed reacts with sand, which is mainly silicon dioxide. • This reaction forms slag which runs down the furnace and then floats on the iron. LIMESTONE
  22. 22. Cs Cs+ reacts with water Electrolysis Rb Rb+ K K+ Na Na+ Li Li+ Ba Ba2+ Sr Sr2+ Ca Ca2+ Mg Mg2+ reacts with acidsAl Al3+ C included for comparison Mn Mn2+ reacts with acids smelting with coke Zn Zn2+ Cr Cr2+ Fe Fe2+ Cd Cd2+ Co Co2+ Ni Ni2+ Sn Sn2+ Pb Pb2+ H2 H+ included for comparison Sb Sb3+ may react with some strongly oxidizing acids heat or physical extraction Bi Bi3+ Cu Cu2+ Hg Hg2+ Ag Ag+ Au Au3+
  23. 23. The paradigm here is that the most reactive metals such as Sodium is extracted through electrolysis. The less reactive metals, typically those lower than Carbon in the reactivity series are extracted via the Blast Furnace. Lastly, those metals such as gold which are extremely unreactive are usually not extracted because they are so unreactive that they can often be found native or simply alone, by themselves. EXPLANATION
  24. 24. 1. Iron Ore: Iron ore is extracted via reduction through the blast furnace. Iron (III) Oxide + Carbon Monoxide → Iron + Carbon Dioxide 1. Aluminium Ore: This is usually just aluminium oxide. Aluminium is higher than carbon in the reactivity series, so it is therefore extracted through electrolysis. Aluminium Oxide → Aluminium + Oxygen Nice and simple. 1. Zinc Blende. Usually just Zinc Sulfide. This is roasted in air to produce Zinc Oxide and Sulfur Dioxide Zinc Sulfide + Oxygen → Zinc Oxide + Sulfur Dioxide EXAMPLES OF REACTIONS
  25. 25. • 1 Explain the use of aluminium in aircraft manufacture in terms of the properties of the metal and alloys made from it. • 3 Explain the use of aluminium in food containers because of its resistance to corrosion. • 2 Explain the use of zinc for galvanising steel, and for sacrificial protection. 10.4 USES OF METALS
  26. 26. AIR AND WATER
  27. 27. • 1 Describe a chemical test for water. • 2 Describe and explain, in outline, the purification of the water supply by filtration and chlorination. • 3 State some of the uses of water in industry and in the home. • 5 Describe the composition of clean air as being a mixture of 78% nitrogen, 21% oxygen and small quantities of noble gases, water vapour and carbon dioxide. • 6 State the common air pollutants as carbon monoxide, sulfur dioxide and oxides of nitrogen, and describe their sources. • 9 State the adverse effect of common air pollutants on buildings and on health. • 10 Describe the formation of carbon dioxide: • as a product of complete combustion of carbon-containing substances, • as a product of respiration, • as a product of the reaction between an acid and a carbonate. C11. AIR AND WATER
  28. 28. • 12 Describe the rusting of iron in terms of a reaction involving air and water, and simple methods of rust prevention, including paint and other coatings to exclude oxygen. • 13 Describe the need for nitrogen-, phosphorus- and potassium-containing fertilisers. • 14 Describe the displacement of ammonia from its salts by warming with an alkali. • 4 Describe the separation of oxygen and nitrogen from liquid air by fractional distillation. • 7 Explain the presence of oxides of nitrogen in car exhausts and their catalytic removal. • 8 Explain why the proportion of carbon dioxide in the atmosphere is increasing, and why this is important. • 11 Describe the essential conditions for the manufacture of ammonia by the Haber process including the sources of the hydrogen and nitrogen, i.e. hydrocarbons or steam and air. AIR AND WATER
  29. 29. • Here are a few ways in which you can use to test for the presence of water: • Test the liquids boiling point. Water boils at precisely 100 degrees and freezes at exactly 0 degrees. • If you add water to Anhydrous Copper Sulphate Powder, it forms a blue solution and may give out heat. • Add Anhydrous Cobalt Chloride which is blue in color. If water is present, should change to color pink. CHEMICAL TEST FOR WATER
  30. 30. • Water extracted from the earth is always infested with impurities. This water might be contaminated with disease and bacteria. That is why it is crucial to ―purify‖ the water before it is drank. This is done by two processes, Filtration and Chlorination. • Here is how it works: • Water is extracted from reservoirs and sent to be ―treated‖ • The water is first passed through a filter to filter out large objects such as rocks or mud. • Smaller particles in the water is removed by adding Aluminium Sulfate which causes the smaller particles to stick together in large pieces and settle down the filter. • Water is now passed through sand and gravel filters which continue to filter off the smaller particles and kills bacteria. • Now its time for chlorination • Chlorine gas is first bubbled through the water to kill the bacteria that exists in the water. • Sodium Hydroxide may be added in the water to prevent the water from being acidic from the chlorine. • Water is delivered to the people that need them. PURIFICATION OF WATER
  31. 31. Irrigation Cooling Recreation Agricultural Industrial use Shower USES OF WATER
  32. 32. FRACTIONAL DISTILLATION • Clean air is cooled to around -80 degrees, Carbon Dioxide sublimes into a solid, water vapour condenses then freezes into ice to be collected. • Cold Air is put into a compressor which increases the pressure to around 100 atm. This causes the air to warm up. • The re-cooled, compressed is now allowed to expand and lose its pressure, which allows it to cool further. • The air is again compressed and then expanded to continue to be cooled. This continues until all liquids liquefy. • The cold air is brought into a fractionating column (as seen above) and slowly left to warm. • Gases separate according to their boiling points. The gas with the lowest boiling points evaporate first.
  35. 35. CARBON MONOXIDE • Poisonous pollutant of air • Main source is factories that burning Carbon-containing fossil fuels as carbon is one of the products of incomplete combustion of fossil fuels.
  36. 36. • Contributes to acidic rain • Main Source comes from two products: 1. Combustion of sulphur 2. Extraction of metals from their sulfide ores • Mixes with water vapour of cloud and air. • This forms Sulphuric Acid (H2SO4) • When it rains, the rain water becomes acidic . • Acidic water is dangerous because it causes the death of sea creatures, acidifies soil which can cause death to plants and cause deforestation. • May also cause lung cancer SULPHUR DIOXIDE
  37. 37. • Formed in high temperatures when nitrogen and oxygen react. • In Cars, the engine operates at a high temperature, giving the nitrogen and the oxygen in the air and engine a chance to react, hence forming nitrogen monoxide. Nitrogen monoxide further reacts with the oxygen in the air to form Nitrogen Oxide. • Nitrogen oxide is dangerous in that it also rises in the air and mixes with rain water to form nitric acid. This can also cause acid rain • Additionally, Nitrogen oxygen can cause certain respiratory problems. OXIDES OF NITROGEN
  38. 38. • Oxides of nitrogen are present in car exhausts, and these can cause problems both to the environment and us humans. Therefore, scientists need to find a way to remove the ―oxides of nitrogen‖ in cars. • This is done through a catalytic converter • The catalytic converter is fitted at the end of the car exhaust. • The purpose of the catalytic converter which catalyzes the reaction between the Nitrogen Oxide and Carbon Monoxide, which in turn produces two harmless separate gases, nitrogen and carbon dioxide. The carbon dioxide comes from the fact that carbon is already present in the cars engine. THE PRESENCE OF OXIDES OF NITROGEN IN CAR EXHAUSTS
  39. 39. Equation of the Reactions 2NO + 2CO → 2CO2 + N2 Nitrogen Oxide + Carbon Monoxide → Carbon Dioxide + Nitrogen 2NO2 + 4CO → 4CO2 + N2 Nitrogen Dioxide + Carbon Monoxide → Carbon Dioxide + Nitrogen
  40. 40. • The Sun sends energy to the earth in two discrete forms, heat and light. • Some of the heat is reflected back to the sun/space, but some is trapped in the earth. • This is caused by the existence of some gases and we call this the Greenhouse effect. • The primary Greenhouse gases are Carbon Dioxide and Methane. • The greenhouse effect is a serious threat to our world. The reason for this can be described by the proliferation of greenhouse gases which causes the greenhouse effect. Increased combustion of carbon in industries which mass produce Carbon Dioxide as a side product and the cutting down of trees which release CO2 via respiration are two major reasons why the greenhouse effect is becoming more serious. • The increase of heat trapped in the earth causes an average rise in sea level and global average temperatures, and we call this effect Global warming INCREASE IN CARBON DIOXIDE
  41. 41. • Formed in power stations by the complete combustion of Carbon containing fuels. • Formed as a product as respiration. • When an acid reacts with a carbonate, Carbon Dioxide is usually formed. FORMATION OF CARBON DIOXIDE
  42. 42. THE HABER PROCESS • The Haber Process manufactures Ammonia from Hydrogen and Nitrogen) • The reaction is as follows: • N2 + 3 H2 ⇌ 2 NH3 • Conditions required to manufacture this: • High temperature (400-450 C ) • Iron catalyst • High pressure • Sources: • Hydrogen – from natural gases • Nitrogen – from the air
  43. 43. SULFUR
  44. 44. • 1 Describe the manufacture of sulfuric acid by the Contact process, including essential conditions. • 2 Describe the properties of dilute sulfuric acid as a typical acid. C12. SULFUR
  45. 45. The Contact Process is a method used to produce Sulphuric Acid. CONTACT PROCESS Conditions for Contact Process to occur • 450C° • 2-9 atm (pressure) • Vanadium Pent-oxide (V2O5) Catalyst
  46. 46. Colored Corrosive liquid Strong oxidizing agent Reacts violently with bases. Doesn’t conduct electricity Insoluble in Water Brittle PROPERTIES OF DILUTE SULFURIC ACID
  47. 47. CARBONATES
  48. 48. 1 Describe the manufacture of lime (calcium oxide) from calcium carbonate (limestone) in terms of the chemical reactions involved, and its uses in treating acidic soil and neutralising industrial waste products. C13. CARBONATES
  49. 49. • Carbonates are ―salts‖ of Carbonic Acids (H2CO3). • Calcium Carbonate (CaCO3) is an especially important Carbonic Acid. Uses of Calcium Carbonate • Helping extraction of iron from its ore • Manufacture of cement CALCIUM CARBONATE
  50. 50. • One industrial use of Calcium Carbonate is that it can be used to make ―lime‖. This process takes place in a kiln, and is largely based on the thermal decomposition of Calcium Carbonate. Limestone is inserted in the Kiln and then is heated. The bottom of the Kiln is both where air is blown in and where lime is collected. Carbon dioxide is also produced. • We can describe this reaction with a simple equation, which you will have to memorize. • CaCO3 (Limestone) ⇌ CaO (Lime) + CO2 (Carbon Dioxide) MANUFACTURE OF LIME
  51. 51. • Used to neutralize soil acidity in farms. This is because lime is a basic oxide, so therefore can be used to neutralize the acidity of the soil. • Another use is to neutralize sulphur waste in power stations. This is also because Sulphur is acidic whilst lime is a basic oxide. And as we’ve learned before, an acid and a basic involves a process of neutralization. USES OF LIME
  53. 53. • 1 Recall coal, natural gas and petroleum as fossil fuels that produce carbon dioxide on combustion. • 3 Name methane as the main constituent of natural gas. • 4 Describe petroleum as a mixture of hydrocarbons and its separation into useful fractions by fractional distillation. • 5 State the use of: • refinery gas for bottled gas for heating and cooking, • gasoline fraction for fuel (petrol) in cars, • diesel oil / gas oil for fuel in diesel engines. • 2 Understand the essential principle of fractional distillation in terms of differing boiling points (ranges) of fractions related to molecular size and intermolecular attractive forces. • science-introduction-to-organic-compounds/ 14.1 FUELS
  54. 54. FOSSIL FUELS Natural gas, coal, petroleum(oil) Form over millions of years Produce CO2 during combustion Provides great amount of energy Nonrenewable
  55. 55. Petroleum: These are formed from the remains of dead organisms that fell to the ocean floor and were then buried by the thick sediment. The high pressure in which the dead organisms are buried eventually converts the dead organisms into petroleum, but this is a process that takes millions of years. Natural Gas: This is composed mainly of methane and is often found with petroleum. High temperatures and pressure causes the compounds to break down into gas. Coal: This is the remain of lush vegetation that grew in ancient swamps. Over the millions of years, high pressure and heat eventually converted the vegetation into coal. REASONS
  56. 56. USES Refinery gas-bottled gas for heating and cooking (natural gas, methane, propane, butane ) Gasoline-fuel in cars Diesel Oil / Gas Oil-fuel in diesel engines
  57. 57. Mixture of hydrocarbons and its separation into useful fractions by fractional distillation PETROLEUM
  58. 58. FRACTIONAL DISTILLATION Separation of a mixture into its component parts Principle-Every liquid has a different boiling point Higher molecular size=Higher BP Stronger intermolecular forces=Higher BP
  59. 59. Petroleum is a mixture of hundreds and hundreds of different hydrocarbons. Putting all these mixtures together isn’t really productive. In order to solve this problem, we have to refine the petroleum in the process of Fractional Distillation. Acknowledge fractional distillation in terms of differing boiling points of fractions related to molecular size and attractive forces. The compounds with large molecules are likely to have a higher boiling point, so therefore condense faster and are collected on a lower position in the fractionating column. BOILING POINTS
  60. 60. FRACTIONAL DISTILLATION Steps: 1. When you heat the petroleum, the compounds start to evaporate as particles will more Kinetic Energy and therefore will more likely be able to break bonds. The compounds which are smaller and lighter evaporate first as it takes less energy to evaporate these. 2. The hot vapour rises and the vapour then condenses in the cool test tube. 3. when the thermometer reaches 100 degrees, the first test tube is then replaced with an empty one. The liquid in the first test tube is the first fraction from the distillation. 4. Repeat, replacing the test tube at 150 degrees, 200 degrees, and 250 degrees.
  61. 61. FRACTIONATING TOWER Petroleum is pumped in at the base. The compounds start to evaporate. Those with the smallest molecules evaporate off first, and rise to the top of the tower. Others rise only part of the way, this is entirely dependent on their boiling points, and then condenses. The compounds are collected in their respective levels before they condense.
  62. 62. Refinery gas Used for bottled gas for heating and cooking, Gasoline fraction Used for fuel (petrol) in cars. Diesel oil/gas oil Used for fuel in diesel engines. USES
  63. 63. • 1 Identify and draw the structures of methane, ethane, ethene and ethanol. • 3 State the type of compound present, given a chemical name ending in - ane, -ene and -ol, or a molecular structure. • 2 Describe the concept of homologous series of alkanes and alkenes as families of compounds with similar properties. • 4 Name, identify and draw the structures of the unbranched alkanes and alkenes (not cis-trans), containing up to four carbon atoms per molecule. 14.2 INTRODUCTION TO ORGANIC COMPOUNDS
  64. 64. METHANE • Main component of natural gas
  65. 65. ETHANE
  66. 66. ETHENE
  67. 67. ETHANOL
  68. 68. ALKANES Simplest organic compound Single bonds Covalently bonded Composed of only Hydrogen and Carbon Generally unreactive Combustible
  69. 69. The chemistry of carbon compounds is called organic chemistry. There are millions of organic chemicals, but they can be divided into groups called homologous series. All members of a particular series will have similar chemical properties and can be represented by a general formula. Members in a Homologous Series have: • Same chemical reactions • Same functional group (Eg. –OH, ‐COOH) • Same general formula, Alkanes CnH2n+2, Alkenes CnH2n • Similar, but Different Physical Properties The alkane series is the simplest homologous series. The main source of alkanes is from crude oil. The first five members of this homologous series are: Methane, Ethane, Propane, Butane, Pentane ALKANES AND ALKENES: HOMOLOGOUS SERIES
  70. 70. -ane will usually be a Alkane. -ene will usually form compound Alkene. -ol will usually form Alcohol. -yne will usually form Alkyne ENDINGS
  71. 71. PRODUCTS OF COMBUSTION Methane Carbon Dioxide Water
  72. 72. • 1 Describe the properties of alkanes (exemplified by methane) as being generally unreactive, except in terms of burning. • 2 State that the products of complete combustion of hydrocarbons, exemplified by methane, are carbon dioxide and water. • 3 Name cracking as a reaction which produces alkenes. • 5 Recognise saturated and unsaturated hydrocarbons • from molecular structures, • by their reaction with aqueous bromine. • 4 Describe the manufacture of alkenes by cracking. • 6 Describe the addition reactions of alkenes, exemplified by ethene, with bromine, hydrogen and steam. 14.3 HYDROCARBONS
  73. 73. Alkanes are generally quite unreactive, and they do not combine well with other substances. The only exception to this is when you burn the alkane, especially methane, in the air with oxygen SINGLE BONDS PROPERTIES OF ALKANES
  74. 74. If you burn a hydrocarbon in the air with oxygen, the hydrocarbon undergoes a process called combustion, and produces Carbon Dioxide + Water. E.g. Methane + Oxygen –> Carbon Dioxide + Water CH4 + 2O2 → CO2 + 2H2O PRODUCTS OF COMPLETE COMBUSTION
  75. 75. In the exam, if they give you a question showing a process where an alkane is being manufactured into alkenes, you can confidently put down cracking as the process which turns the alkane into an alkene. • You can make an alkene from an alkane through a process called cracking. • Cracking is basically a process where you break down heavier molecules into lighter hydrocarbons, as there is little industrial use for these heavy hydrocarbons. INA REFINERY How cracking takes place in a refinery? Long chain hydrocarbon is heated to be vaporized. The vapour is passed through a catalyst. Thermal decomposition takes place, and the alkane is decomposed into the smaller alkenes. CRACKING
  76. 76. CRACKING • H2 is produced in the cracking process. • High temperature is needed • Catalyst speeds up the reaction. • Obviously, cracking ethane is an example of cracking short hydrocarbons. Most hydrocarbons are very long in terms of their molecular structure, which is why they have to be cracked in the first place!
  77. 77. • From molecular structures, • By their reaction with aqueous bromine. Saturated Hydrocarbons have single C-C bonds between the atoms. Examples of saturated hydrocarbons Unsaturated Hydrocarbons have C=C double bonds. Examples of unsaturated hydrocarbons are alkenes. • Molecular Structures Saturated Hydrocarbons have C-C single bonds whilst C=C is a double bond • Reaction with aqueous bromine Get some orange solution bromine water and the suspected hydrocarbon Add a few drops of bromine to the hydrocarbon If the solution decolorizes (color disappears), a unsaturated hydrocarbon is present. SATURATED AND UNSATURATED HYDROCARBONS
  78. 78. ―An addition reaction is a process where an unsaturated alkene is turned to a saturated compound”. We’re going to learn how we form ethanol from ethane. When you crack ethane, you form ethene. As a result, hydrogen is also produced. Ethene can react with hydrogen again, under heat, pressure and a catalyst to form ethane Ethene can add on with water (steam) to form ethene Ethene + Steam → Ethanol ADDITION REACTIONS
  79. 79. • 1 State that ethanol may be formed by reaction between ethene and steam. • 3 Describe the complete combustion reaction of ethanol. • 4 State the uses of ethanol as a solvent and as a fuel. • 2 Describe the formation of ethanol by the catalytic addition of steam to ethene. 14.4 ALCOHOLS
  80. 80. Hydration: Basically means water is added on. An Addition Reaction HYDRATION Ethene + Steam —> Ethanol C2H4 + H2O —> C2H5OH • Reaction is reversible • Exothermic • High pressure and low temperature would give the highest yield. • Catalyst is used to speed up the reaction.
  81. 81. Ethanol burns quite well in oxygen to give out heat: C2H5OH (l) + 3O2 (g) → 2CO2 (g) + 3H2O (l) + heat Additionally, carbon dioxide and water vapour is formed as a product. COMBUSTION REACTION OF ETHANOL
  82. 82. 1) Ethanol is often used a fuel. 2) Ethanol is often used as fuel because: It can be made quite cheaply. Many countries lack petroleum and need to import from other nations, so ethanol seems more cost effective. Less impact on Carbon Dioxide levels are compared to fossil fuels. Used for: Motor Fuel, Rocket fuel As a solvent Ethanol is the alcohol in alcoholic drinks such as vodka. Its a good solvent because it easily dissolves many substances that do not dissolve in water. Evaporates easily so it is a suitable solvent to use in glues, printing inks, perfumes, and aftershave. ETHANOL
  83. 83. USES OF ETHANOL Drinks The "alcohol" in alcoholic drinks is simply ethanol. Industrial methylated spirits (meths) Ethanol is usually sold as industrial methylated spirits which is ethanol with a small quantity of methanol added and possibly some colour. Methanol is poisonous, and so the industrial methylated spirits is unfit to drink. This avoids the high taxes which are levied on alcoholic drinks (certainly in the UK!). As a fuel Ethanol burns to give carbon dioxide and water and can be used as a fuel in its own right, or in mixtures with petrol (gasoline). "Gasohol" is a petrol / ethanol mixture containing about 10 - 20% ethanol. Because ethanol can be produced by fermentation, this is a useful way for countries without an oil industry to reduce imports of petrol. As a solvent Ethanol is widely used as a solvent. It is relatively safe, and can be used to dissolve many organic compounds which are insoluble in water. It is used, for example, in many perfumes and cosmetics.
  84. 84. Ethanol can be used as a solvent and a fuel
  86. 86. • 1 Describe macromolecules in terms of large molecules built up from small units (monomers), different macromolecules having different units. 14.5 MACROMOLECULES
  87. 87. • Macromolecules are sometimes also called polymers. • An individual unit of a polymer is called a ―monomer‖. Lets just say the monomer was one bead of the necklace. A group of many monomers stringed together will form a ―Macromolecule‖. • And obviously, different macromolecules will be built out of different units. MACROMOLECULES
  88. 88. • 1 Describe the formation of poly(ethene) as an example of addition polymerisation of monomer units. • 2 Draw the structure of poly(ethene). • 3 Describe the formation of a simple condensation polymer exemplified by nylon, the structure of nylon being represented as: 14.6 SYNTHETIC POLYMERS
  89. 89. A polymer is a substance that contains large molecules formed by many small molecules added together. Let’s take ethene as an example A polymer that is made from ethene is called ―Poly-ethene‖. Poly- basically just means many. We often call this reaction Polymerisation, or polymerization if you’re American. In a polymerization reaction, what essentially happens is that thousands or smaller molecules join to form a macromolecule. We call these small molecules monomers. FORMATION OF POLY(ETHENE)
  90. 90. POLYETHENE
  91. 91. • Double bonds break, which allows monomers molecules to ultimately join together. However, in condensation polymer, no double bonds break. Alternatively: • Two different monomers join. • The monomers join at their function groups by eliminating small molecules. • Go on google and find the structure of Diaminohexane and Hexan-1,6 Dioyl Chloride. • Now, lets call them A and B respectively. • A has an NH2 group at each end. B has a COCl group at each end. Only these parts, called functional groups take part in the reaction. • The nitrogen atom at one end of ―A‖ has joined to the carbon atom at one end of B, by eliminating a molecule of hydrogen chloride. • This continues at the other ends of A and B CONDENSATION POLYMER
  92. 92. • 1 Describe proteins as possessing the same (amide) linkages as nylon but formed from the linking of amino acids. • 2 State that proteins can be hydrolysed to amino acids under acid or alkaline conditions. (Structures and names are not required.) 14.7 NATURAL MACROMOLECULES
  93. 93. Proteins are polymers formed from amino acids. Amino Acids Form Firstly, protein consists of the elements: Carbon Nitrogen Sulphur Hydrogen Oxygen PROTEINS
  94. 94. The OH and H make a water molecule which is then ―eliminated‖ Step 1 Just like nylon, we have amide linkage in the place I circled above, but this time it is composed of amino acids. Step 2 State: Proteins can be hydrolysed to amino acids under acid or alkaline conditions. Hydrolysis is basically just a process where molecules are broken down upon reaction with water.