Chemistry IGCSE Textbook

NES/Chemistry/IGCSE Topic 11 - Air and Water 11.1 Water  Describe chemical tests for water using cobalt(II) chloride and copper(II) sulfate  Describe, in outline, the treatment of the water supply in terms of filtration and chlorination  Name some of the uses of water in industry and in the home  Discuss the implications of an inadequate supply of water, limited to safe water for drinking and water for irrigating crops 11.2 Air  State the composition of clean, dry air as being approximately 78% nitrogen, 21% oxygen and the remainder as being a mixture of noble gases and carbon dioxide  Name the common pollutants in the air as being carbon monoxide, sulfur dioxide, oxides of nitrogen and lead compounds  State the source of each of these pollutants: – carbon monoxide from the incomplete combustion of carbon- containing substances – sulfur dioxide from the combustion of fossil fuels which contain sulfur compounds (leading to ‘acid rain’) – oxides of nitrogen from car engines – lead compounds from leaded petrol  State the adverse effect of these common pollutants on buildings and on health and discuss why these pollutants are of global concern  State the conditions required for the rusting of iron  Describe and explain methods of rust prevention, specifically paint and other coatings to exclude oxygen  Describe the separation of oxygen and nitrogen from liquid air by fractional distillation  Describe and explain the presence of oxides of nitrogen in car engines and their catalytic removal  Describe and explain sacrificial protection in terms of the reactivity series of metals and galvanising as a method of rust prevention 200

NES/Chemistry/IGCSE 11.3 Nitrogen and fertilisers  Describe the need for nitrogen-, phosphorus- and potassium- containing fertilisers  Describe the displacement of ammonia from its salts  Describe and explain 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 11.4 Carbon dioxide and methane  State that carbon dioxide and methane are greenhouse gases and explain how they may contribute to climate change  State 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 – from the thermal decomposition of a carbonate  State the sources of methane, including decomposition of vegetation and waste gases from digestion in animals  Describe the carbon cycle, in simple terms, to include the processes of combustion, respiration and photosynthesis 201

NES/Chemistry/IGCSE 11.1 Water Tests for Water Test Physical Result or anhydrous cobalt(II) chloride paper paper turns from blue to pink anhydrous copper(II) sulfate paper Chemical from white powder to blue crystals test the melting point of the solid chemical melting point of the solid is fixed at 0oC chemical boiling point is fixed at 100oC and boiling point of the liquid physical Purification of Water Water used in our homes comes from rivers, lakes, underground water supplies and in Kuwait it comes from the sea. Before we use it, the water must be purified. Stage 1: The water is filtered to remove insoluble solids Stage 2: Chlorine is added to kill bacteria A limited supply of clean water is the main cause of disease and crop failure. Uses of Water In the Home washing clothes In Industry flushing toilets making drinks, eg Pepsi cooling powerstations 202

NES/Chemistry/IGCSE 11.2 Air Composition of Clean Air Clean air has no pollutants in it and is made up of a mixture of different gases. Gases in Clean Air % Nitrogen 78 Oxygen 21 0.03 Carbon Dioxide about 1% Noble Gases varies depending on humidity Water Vapour Properties of Oxygen and Nitrogen Oxygen Nitrogen Atomic symbol O Atomic symbol N Molecular formula O2 Molecular formula N2 Boiling point -183oC Boiling point -196oC colourless, odourless gas colourless, odourless gas slightly soluble in water less soluble than oxygen solution is neutral solution is neutral does not burn, but other substances react only burns at high temperature and with oxygen when they burn pressure - eg car engine 203

NES/Chemistry/IGCSE Gas Uses of the Gases in Air Oxygen Use oxygen tents and breathing apparatus in hospitals combusted with acetylene (a hydrocarbon) to produce a very high temperature flame which is used to weld metals together to convert cast iron to steel mountaineers and deep sea divers use oxygen Nitrogen for making ammonia, which is then used to make mainly fertilisers and nitric acid as a refrigerant food packaging e.g. crisps Carbon dioxide added to make fizzy drinks e.g. Pepsi fire extinguishers. The heavy gas smothers the fire, preventing it obtaining oxygen Noble Gases Helium is less dense than air and so is used to fill airships and weather balloons Argon is used to provide an inert atmosphere in lamps to prevent the filament burning Neon is used in advertising lights because it glows when an electric current is passed through it. Separating the Different Gases in Air Air is a mixture of gases and the gases have different boiling points and densities. There are two ways of separating the gases in air.  Method 1: Fractional distillation - clean air is liquefied using a low temperature and high pressure and then the different components are separated by fractional distillation.  Method 2: Diffusion - air is passed through a porous tube. The gas with the lowest density diffuses into the porous tube at a faster rate. 204

NES/Chemistry/IGCSE Air Pollution Apart from the gases normally found in the air, other gases such as carbon monoxide, sulfur dioxide and oxides of nitrogen and can be present; as well as solid lead compounds. Carbon dioxide is not considered a pollutant as it is already in air. Pollution is the release of harmful substances into the environment as a result of human activity. Pollutant Source of Pollutant Problems Caused by the Pollutant poisonous because carbon monoxide Carbon incomplete combustion of carbon combines more readily than oxygen Monoxide containing fuels with red blood cells Sulfur Dioxide:  sore throats  asthma attacks Sulfur combustion of fossil fuels which Sulfuric Acid (acid rain): Dioxide contain sulfur as an impurity  corrodes exposed metal work  damages trees and plants Oxides of formed in car engines (high  erodes limestone buildings and Nitrogen temperature and high pressure) leaded petrol statues Lead Nitric acid (acid rain): Compounds  corrodes exposed metal work  damages trees and plants  erodes limestone buildings and statues lead causes damage to the brain and nerve cells in young children. Catalytic converters In car engines, there is always some carbon monoxide made from incomplete combustion and oxides of nitrogen from the nitrogen in air burning as well. These pollutant gases can be removed from the exhaust gases using a catalytic converter. The reactions that take place can be summarised as: 2CO(g) + 2NOx(g)  2CO2(g) + N2(g) 205

NES/Chemistry/IGCSE The carbon monoxide is oxidised to carbon dioxide and the oxides of nitrogen are reduced to nitrogen. Any soot (unburnt fuel - CxHy) is also oxidised to carbon dioxide and water. The catalyst is a mixture of platinum and rhodium. catalytic converter gases from engine gases into the environment CO NOX CO2 CXHY N2 H2O The catalyst has an optimum working temperature of about 200oC. The catalyst is not effective at removing the polluting gases until the engine has warmed up, which takes about 10 minutes. Unleaded petrol has to be used otherwise the lead poisons the platinum catalyst and stops it from working. Corrosion and Rusting Corrosion is the name given to the process that takes place when metals and alloys react with oxygen, water or any other substance found in their immediate environment. Rusting is the corrosion of iron and steel to form hydrated iron(III) oxide (Fe2O3.xH2O). Rust crumbles easily and the iron, or steel will lose its strength. Two substances, which are both necessary for rusting, are:  water, or the water in air  oxygen, or the oxygen in air 4Fe + 2xH2O + 3O2  2Fe2O3.xH2O Rusting will happen faster if salt water is used because it contains ions which can transfer electrons and speed up the reaction. 206

NES/Chemistry/IGCSE Rust Prevention Metal Object Method Note Car bodies if the paint is scratched, the Paint iron beneath it starts to Bridges rust. Moving parts of Oil or Grease machinery prevents water getting to Galvanising the iron Bicycle chain Coating with plastic Steel girders long lasting and easy to used in bridges apply and buildings Freezers PVC is used to coat steel preventing it lasts a long time Food can from being in contact with oxygen and water. Tin plating tin does not easily corrode steel is coated with a layer of tin. and is not poisonous. Zinc cannot be used for food cans because zinc and its compounds are poisonous. Ships Sacrificial protection allowing a more reactive metal to corrode instead Oil rigs Cathodic protection using a power source to get another metal to corrode instead 207

NES/Chemistry/IGCSE Galvanising Galvanising is the process where iron is coated with a surface layer of zinc zinc Zinc is used to protect iron or steel from rusting. The zinc layer is iron impermeable to oxygen and water, preventing them coming in contact with the iron. This is an example of a physical barrier. Also, if the zinc layer gets scratched the iron will still not rust as the zinc is more reactive and act as sacrificial protection. Sacrificial Protection If the zinc gets scratched revealing iron, the iron still zinc layer scratched O2 + H2O does not rust. This is because the zinc, being more exposing the iron reactive than iron, reacts with water and oxygen to O2 + H2O forming its positive ions in preference to the iron. The electrons produced go to the iron preventing corrosion iron in a process called ‘sacrificial protection’. Therefore the zinc reacts and the iron remains intact. This is an example of a chemical barrier. oxidation Zn  Zn2+ + 2e– Sacrificial protection is used to protect ships and oilrigs from rusting using magnesium, or zinc as the more reactive metal. 208

NES/Chemistry/IGCSE Cathodic Protection power steel oil rig which is the +– cathode titanium sea water which anode contains: Na+(aq), H+(aq), OH–(aq), Cl–(aq) At the anode OH–(aq) ions and Cl–(aq) ions are oxidised and lose electrons to the anode and so oxygen gas and chlorine gas are formed at the anode. These electrons are pumped round the external circuit by the power supply to the cathode, the oil rig. The steel oil rig cannot not rust because it receives a supply of electrons which are produced at the anode and so the iron cannot be oxidised. How does Sacrificial Protection Differ from Cathodic Protection?  Sacrificial protection needs a more reactive metal as the anode in contact with the iron or steel but cathodic protection needs an inert metal as the anode in contact with the iron or steel.  Sacrificial protection does not need electricity, but cathodic protection requires electricity. 209

NES/Chemistry/IGCSE 11.3 Nitrogen and Fertilisers Nitrogen, from air, is used to make ammonia, nitric acid and nitrogen fertilisers. The Haber Process This is a process where ammonia is made on a large scale for profit. N2(g) + 3H2(g) ⇌ 2NH3(g) H = - 92kJ The forward reaction is exothermic (H = - 92kJ) and the backward reaction is endothermic (H = + 92kJ) Raw Materials Used Conditions for Haber Process Natural Gas Temperature of 450oC Steam Pressure of 200 atmospheres Nitrogen from Air Finely divided iron catalyst Making the Raw Materials for the Haber Process 1. Manufacture of hydrogen gas for the reaction This comes from methane gas (CH4) by reacting it with steam at a temperature of 750oC and using a nickel based catalyst. CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) The carbon monoxide then reacts with more steam to form more hydrogen and carbon dioxide gas. CO(g) + H2O(g) ⇌ H2(g) + CO2(g) 2. Manufacture of nitrogen gas for the reaction Nitrogen gas is produced by the fractional distillation of clean liquid air. 210

NES/Chemistry/IGCSE Optimum Conditions for the Haber Process Temperature Lowering the temperature decreases the rate of reaction but increases the yield of ammonia as equilibrium position moves in the exothermic direction. Increasing the temperature increases the rate of reaction but decreases the yield of ammonia equilibrium position moves in the endothermic direction. The 450oC temperature used is high enough to give a good rate of reaction but low enough to give a good yield. Pressure Decreasing the pressure decreases the rate of reaction and decreases the yield of ammonia as equilibrium position moves to the side with more gas mole. Increasing the pressure increases the rate of reaction and increases the yield of ammonia as equilibrium position moves to the side with less gas mole, but the cost of the process increases. The 200 atmosphere pressure used is a compromise between obtaining a reasonable yield with a reasonable rate of reaction at a reasonable cost. Recycling the Unused Hydrogen and Nitrogen The hot gases are cooled to liquefy the ammonia. Ammonia has a higher boiling point than nitrogen or hydrogen and so condenses to form a liquid. The unreacted nitrogen and hydrogen gas are recycled by passing over the catalyst again. The yield of ammonia is about 15% of the total gas provided. The liquid ammonia is run off from the reaction vessel. 211

NES/Chemistry/IGCSE NPK Fertilisers Plants require three essential elements for healthy plant growth. They are: 1. Nitrogen (N) 2. Phosphorus (P) 3. Potassium (K) All plants need nitrogen to make proteins, in the form of nitrates, which are all soluble in water and so can be taken up by the plants' roots. This is how plants get nitrogen. They cannot take in nitrogen gas because they have not evolved a way of absorbing it from air and converting it into nitrates. Nitrogen promotes plant growth and higher crop yields. 212

NES/Chemistry/IGCSE 11.4 Carbon Dioxide and Methane Respiration is the production of energy from food by living organisms. Both carbon dioxide and methane are greenhouse gases, which may contribute to climate change. If the amount of CO2 and CH4 builds up in the atmosphere, the average temperature of the Earth may rise. The effect is known as the greenhouse effect. Carbon Dioxide Carbon dioxide is added to the atmosphere by: 1. Complete combustion 2. Respiration 3. Acid - carbonate reactions 4. Thermal decomposition of carbonates These processes cause the % carbon dioxide in the atmosphere to increase. 1. Complete Combustion Carbon dioxide is made when any carbon-containing fuel is burned. This includes all fossil fuels (see Topic 14).  Example 1: Combustion of methane CH4(g) + 2O2(g)  CO2(g) + 2H2O(l) 2. Respiration Carbon dioxide is the product of aerobic respiration by living organisms.  Example 2: Respiration C6H12O6 + 6O2  6CO2 + 6H2O + energy 213

NES/Chemistry/IGCSE 3. Acid - Carbonate Reactions Carbon dioxide is produced in the reaction between an acid and carbonate.  Example 3: magnesium carbonate and hydrochloric acid MgCO3(s) + 2HCl(aq)  MgCl2(aq) + H2O(l) + CO2(g) Carbon dioxide is removed from the atmosphere by: 1. Photosynthesis This processes cause the % carbon dioxide in the atmosphere to decrease. 1. Photosynthesis Plants take in atmospheric CO2(g) in a photochemical reaction to make carbohydrates.  Example 4: Photosynthesis 6CO2 + 6H2O  C6H12O6 + 6O2 Glucose (a carbohydrate) can then be made into complex carbohydrates such as starch and cellulose by condensation polymerisation (see Topic 14). Carbon Cycle Carbon dioxide is being constantly added to the atmosphere by combustion and respiration and removed from the atmosphere by photosynthesis. Methane Sources of methane:  Main component in natural gas  Decomposition of vegetation  Waste gases from digestion in animals 214

NES/Chemistry/IGCSE Topic 12 - Sulfur  Name some sources of sulfur  Name the use of sulfur in the manufacture of sulfuric acid  State the uses of sulfur dioxide as a bleach in the manufacture of wood pulp for paper and as a food preservative (by killing bacteria)  Describe the manufacture of sulfuric acid by the Contact process, including essential conditions and reactions  Describe the properties and uses of dilute and concentrated sulfuric acid 215

NES/Chemistry/IGCSE Sources of Sulfur  As the element sulfur in underground deposits in the USA and Poland  Zinc blende, the ore which contains zinc sulfide (ZnS) Uses of Sulfur  Manufacture of sulfur dioxide and sulfuric acid  Vulcanisation of rubber, to make it harder Uses of Sulfur Dioxide  To bleach wood pulp, to make paper  As a food preservative, by killing bacteria  Manufacture of sulfuric acid Contact Process This is the process used to make sulfuric acid from sulfur. It has four main steps: 1. Combustion of sulfur 2. Further oxidation of sulfur dioxide 3. Producing oleum 4. Producing sulfuric acid Oleum is the name for H2S2O7 1. Combustion of sulfur S + O2  SO2 216

NES/Chemistry/IGCSE 2. Further oxidation of sulfur dioxide 2SO2 + O2 ⇌ 2SO3 (H negative) As this is an equilibrium reaction, the optimum % yield and rate are obtained by the following conditions: 450oC 3atm vanadium(V) oxide catalyst 3. Producing Oleum SO3 + H2SO4(concentrated)  H2S2O7 Concentrated sulfuric acid cannot be made directly from sulfur dioxide as it is a very exothermic reaction and the acid would boil. This step was added for safety. 4. Producing sulfuric acid H2S2O7 + H2O  2H2SO4 Some of the sulfuric acid made is used for step 3 and the rest is sold as a chemical. Properties of Sulfuric Acid Dilute Sulfuric Acid Concentrated Sulfuric Acid Acts as a regular acid (see Topic 8.1) Dehydrating agent Drying acid, or neutral gases Uses of Sulfuric Acid  Make soapless detergents  Make fertilisers 217

NES/Chemistry/IGCSE Topic 13 - Carbonates  Describe the manufacture of lime (calcium oxide) from calcium carbonate (limestone) in terms of thermal decomposition  Name some uses of lime and slaked lime such as in treating acidic soil and neutralising acidic industrial waste products, e.g. flue gas desulfurisation  Name the uses of calcium carbonate in the manufacture of iron and cement 218

NES/Chemistry/IGCSE Limestone, Lime and Slaked Lime Limestone (as well as chalk and marble) contains calcium carbonate as well as other impurities. Lime, or Quick Lime, is calcium oxide. It is make from limestone. Slaked Lime is solid calcium hydroxide. It is made from lime. Limewater is aqueous calcium hydroxide. It is made from slaked lime. Limestone Cycle Limestone Heat Lime CaCO3 CaO Add CO2 gas Add water drop wise Lime Water Add water to make a solution Slaked Lime Ca(OH)2 (aq) Ca(OH)2 (s) Reactions CaCO3 (s)  CaO (s) + CO2 (g) Limestone: CaO (s) + H2O (l)  Ca(OH)2 (s) Lime: Ca(OH)2 (s)  Ca(OH)2 (aq) Slaked Lime: Ca(OH)2 (aq) + CO2 (g)  CaCO3 (s) Lime Water: 219

NES/Chemistry/IGCSE Uses of Limestone, Lime and Slaked Lime Limestone Lime Slaked Lime Manufacture of iron and Neutralise soil acidity Neutralise soil acidity steel Neutralising acidic Neutralising acidic industrial waste products Manufacture of cement industrial waste products Remove acidic impurities Glass manufacture Used to neutralise excess acidity in lakes and soil in the basic oxygen furnace Controlling Soil Acidity It is important to control soil acidity as plants grow better in soil which is pH 7 and give a higher crop yield. Calcium carbonate (insoluble in water) and calcium oxide (slightly soluble in water) can both be used to increase the pH of acidic soil. It is better to use calcium carbonate to neutralise acidic soil because:  CaCO3 cannot be washed away by rain and remains longer in the soil but CaO could be washed away as it is more soluble.  As CaCO3 is insoluble the pH of the soil cannot rise above pH 7, but with CaO the pH can rise above pH 7. Adding Lime to Soil Containing Artificial Fertilisers When lime, a basic oxide, is added to damp soil containing a nitrogenous fertiliser such as ammonium nitrate, or ammonium sulfate then ammonia gas is released so the concentration of ammonium ions decreases. The lime causes ammonia to be displaced from ammonium ions. 220

NES/Chemistry/IGCSE 14 - Organic Chemistry 14.1 Names of compounds  Name and draw the structures of methane, ethane, ethene, ethanol, ethanoic acid and the products of the reactions stated in sections 14.4– 14.6  State the type of compound present, given a chemical name ending in -ane, -ene, -ol, or -oic acid or a molecular structure  Name and draw the structures of the unbranched alkanes, alkenes (not cistrans), alcohols and acids containing up to four carbon atoms per molecule  Name and draw the structural formulae of the esters which can be made from unbranched alcohols and carboxylic acids, each containing up to four carbon atoms 14.2 Fuels  Name the fuels: coal, natural gas and petroleum  Name methane as the main constituent of natural gas  Describe petroleum as a mixture of hydrocarbons and its separation into useful fractions by fractional distillation  Describe the properties of molecules within a fraction  Name the uses of the fractions as: – refinery gas for bottled gas for heating and cooking – gasoline fraction for fuel (petrol) in cars – naphtha fraction for making chemicals – kerosene/paraffin fraction for jet fuel – diesel oil/gas oil for fuel in diesel engines – fuel oil fraction for fuel for ships and home heating systems – lubricating fraction for lubricants, waxes and polishes – bitumen for making roads 221

NES/Chemistry/IGCSE 14.3 Homologous series  Describe the concept of homologous series as a ‘family’ of similar compounds with similar chemical properties due to the presence of the same functional group  Describe the general characteristics of an homologous series  Recall that the compounds in a homologous series have the same general formula  Describe and identify structural isomerism 14.4 Alkanes  Describe the properties of alkanes (exemplified by methane) as being generally unreactive, except in terms of burning  Describe the bonding in alkanes  Describe substitution reactions of alkanes with chlorine 14.5 Alkenes  Describe the manufacture of alkenes and of hydrogen by cracking  Distinguish between saturated and unsaturated hydrocarbons: – from molecular structures – by reaction with aqueous bromine  Describe the formation of poly(ethene) as an example of addition polymerisation of monomer units  Describe the properties of alkenes in terms of addition reactions with bromine, hydrogen and steam 14.6 Alcohols  Describe the manufacture of ethanol by fermentation and by the catalytic addition of steam to ethene  Describe the properties of ethanol in terms of burning  Name the uses of ethanol as a solvent and as a fuel  Outline the advantages and disadvantages of these two methods of manufacturing ethanol 222

NES/Chemistry/IGCSE 14.7 Carboxylic acids  Describe the properties of aqueous ethanoic acid  Describe the formation of ethanoic acid by the oxidation of ethanol by fermentation and with acidified potassium manganate(VII)  Describe ethanoic acid as a typical weak acid  Describe the reaction of a carboxylic acid with an alcohol in the presence of a catalyst to give an ester 14.8.1 Polymers  Define polymers as large molecules built up from small units (monomers)  Understand that different polymers have different units and/or different linkages 14.8.2 Synthetic polymers  Name some typical uses of plastics and of man-made fibres such as nylon and Terylene  Describe the pollution problems caused by nonbiodegradable plastics  Explain the differences between condensation and addition polymerisation  Deduce the structure of the polymer product from a given alkene and vice versa  Describe the formation of nylon (a polyamide) and Terylene (a polyester) by condensation polymerisation, the structure of nylon being represented as: and the structure of Terylene as: 223

NES/Chemistry/IGCSE 14.8.3 Natural polymers  Name proteins and carbohydrates as constituents of food  Describe proteins as possessing the same (amide) linkages as nylon but with different units  Describe the structure of proteins as:  Describe the hydrolysis of proteins to amino acids (Structures and names are not required.)  Describe complex carbohydrates in terms of a large number of sugar units, considered a joined together by condensation polymerisation, e.g.  Describe the hydrolysis of complex carbohydrates (e.g. starch), by acids or enzymes to give simple sugars  Describe the fermentation of simple sugars to produce ethanol (and carbon dioxide) (Candidates will not be expected to give the molecular formulae of sugars.)  Describe, in outline, the usefulness of chromatography in separating and identifying the products of hydrolysis of carbohydrates and proteins 224

NES/Chemistry/IGCSE 14.1 Names of Compounds Organic compounds are compounds which contain carbon from living things Hydrocarbons are compounds made from hydrogen and carbon only Organic carbon compounds are present in all fossil fuels. Fossil Fuel Composition State Coal Mostly carbon Solid Coke Purified coal Solid Mostly methane Gas Natural gas Mixture of hydrocarbons Liquid Crude oil / Petroleum Coal Coal is a black solid that is mostly made of carbon, with sulfur as an impurity. It burns to produce carbon dioxide (and sulfur dioxide). Coke Coke is a purified form of coal. It contains a higher percentage of carbon. It still has sulfur as an impurity. Natural Gas Natural gas is mostly made of methane (CH4) and produces carbon dioxide and water vapour when burned. Crude Oil Crude oil is a mixture of many different hydrocarbons. It is separated into useful fractions (see Topic 14.2). 225

NES/Chemistry/IGCSE Carbon Chain Molecules Organic carbon molecules consist of a chain of carbon atoms bonded together. In addition other elements can also bond to the chain, such as hydrogen, oxygen, nitrogen and the halogens (fluorine, chlorine, bromine and iodine). Types of Formula 1. Display - where every atom and bond is drawn. This shows the greatest level of detail. 2. Structural - each carbon atom is shown. 3. Molecular - only shows how many of each type of atom there is. No functional group detail is shown. 1. Display Formula These examples show all atoms and all bonds in the molecule.  Example 1: a chain containing just carbon and hydrogen atoms  Example 2: a chain containing carbon, hydrogen and chlorine atoms  Example 3: a chain containing carbon, hydrogen and oxygen atoms 226

NES/Chemistry/IGCSE  Example 4: a chain containing double bonds, carbon, hydrogen and chlorine 2. Structural Formula Each carbon is shown with the atoms joined to it. Not all bonds are shown. Bonds between different carbon atoms in the chain are shown.  Example 5: a chain containing double bonds, carbon, hydrogen and oxygen 3. Molecular Formula Just the molecular formula is written, this does not show any detail of the structure of the molecule, but it does show how many and which atoms are present.  Example 6: a chain containing carbon and hydrogen C3H6 227

NES/Chemistry/IGCSE Naming Organic Molecules The name of an organic molecule is made up of a prefix which depends on how many carbon atoms it contains and a suffix which depends on the functional group present. Number of Carbon Atoms Prefix 1 meth- 2 eth- 3 prop- 4 but- Functional Group Contains Suffix Alkane C-C single bonds -ane Alkene C=C double bonds -ene see example 11 Halogenoalkane R-X -anol Alcohol R-OH -anoic acid R-COOH see examples 12 and 13 Carboxylic Acid R-COO-R' Ester Where: R is part of a carbon chain R' is another carbon chain X is a halogen The position of the functional group also has to be given in the name. Functional Group Where to put Number Alkane none used Alkene alk-x-ene Halogenoalkane x-halogenoalkane Alcohol alcoh-x-ol none used Carboxylic Acid non used Ester 228

NES/Chemistry/IGCSE  Example 7: This is propane as there are 3 carbons in the chain (prop-) and all the carbons are single bonded (-ane)  Example 8: This is butanoic acid as there are 4 carbons in the chain (but-) and there is a carboxylic acid functional group present (-anoic acid)  Example 9: This is but-2-ene as there are 4 carbons in the chain (but-) and there is a double bond (-ene). The -2- is added to show on which carbon the double bond is starts.  Example 10: This is but-1-ene as are 4 carbons in the chain (but-) and there is a double bond (-ene). The -2- is added to show where the double bond starts. CH2=CH-CH2-CH3 229

NES/Chemistry/IGCSE  Example 11: This is 1-chloropropane as there is a chain of 3 carbons (prop-) and all the carbons are single bonded (-ane) and also there is a chlorine atom on the first carbon reading from right to left so (1-chloro-) is added to the beginning of the name. Halogen names in organic molecules are fluoro- chloro- bromo- and iodo- and always go at the start of the molecule's name. Also we can count from either the left, or the right end of the molecule in order to get the lowest possible number for the functional group.  Example 12: This is an ester, their names are slightly different as there are two carbon chains in the molecule. On the right side there are 2 carbons (ethyl-) and on the left side there are 3 carbons and the double bond to the oxygen (-propanoate). So this ester is called ethylpropanoate. All esters have the style ~yl~anoate where the ~ is a meth, eth, prop, or but. It can also be written as CH3CH2COOCH2CH3  Example 13: This is also an ester. It is called methylbutanoate. The carbon chain with the C=O bond always goes second in the name (see Topic 14.7) CH3CH2CH2COOCH3 230

NES/Chemistry/IGCSE 14.2 Fuels A fuel is a substance that burns to release energy A fraction is the distillate collected over a narrow temperature range from a fractionating column Coal, coke and natural gas were covered in Topic 14.1. Crude Oil / Petroleum Petroleum is a mixture of hydrocarbons that have to be separated into useful fractions by fractional distillation. Diagram of a Fractionating Column refinery gas petroleum/ gasoline crude oil naphtha paraffin diesel oil fuel oil lubricating oil bitumen 231

NES/Chemistry/IGCSE  Petroleum is fractionally distilled in tall fractionating columns.  The petroleum is heated until it starts to boil. It is then put into the fractionating column at the bottom.  The liquid fraction (bitumen) falls to the bottom. The rest of the petroleum gases rise up the column.  Each fraction is then collected as it condenses back to a liquid.  The higher up the column, the cooler it gets and fractions are collected in the order of their boiling/condensing points.  Refinery gas is a gas at room temperature, so it is collected at the top of the column. Each fraction contains groups of hydrocarbons with boiling points within a specific range. The lower the boiling point, the higher up the fraction reaches before it condenses. The smaller the molecule is, the lower the boiling point. This is because there are weak intermolecular van der Waals forces of attraction and so a small amount of energy is required to overcome these forces. The larger the molecule is, the higher the boiling point. This is because there are stronger intermolecular forces of attraction and so more energy is required to overcome these forces of attraction. Uses of Petroleum Fractions Fraction Uses Boiling Point Length of /oC Carbon Chain Refinery Gas for bottled gas for heating Petrol / Gasoline and cooking increases increases fuel (petrol) in cars Naphtha for making chemicals Paraffin / Kerosene for jet fuel Diesel Oil / Gas Oil fuel in diesel engines Fuel Oil fuel for ships and home Lubricating Oils heating systems Bitumen for lubricants, waxes and polishes for making roads Lubricants are used to reduce friction between moving parts. All fractions are mixtures of hydrocarbons with the alkane functional group. 232

NES/Chemistry/IGCSE 14.3 Homologous Series This is a group of similar chemicals with the same general formula, the same functional group and each consecutive member differs by a –CH2– A functional group is the part of the molecule which participates in a reaction Structural isomers are different compounds with the same molecular formula, but a different structural formula The general formula of an organic molecule is a mathematical way of expressing the functional group. Each functional group has its own general formula. Structural Isomerism There are two types of isomerism 1. Side Chains 2. Position of Functional Group 1. Side Chains An organic molecule does not have to have all of its carbon atoms in a straight chain, there can be side chains as well. The molecule with a side chain will always have a lower melting and boiling point as the van der Waals forces of attraction are weaker.  Example 14: Butane has an isomers - a straight chain molecule and a molecule with a side chain. They both have the same molecular formula (C4H10). HHHH H CH3H HCCCCH HCCCH HHHH HHH 233

NES/Chemistry/IGCSE 2. Position of Functional Group If the functional group can be in a different position in the carbon chain, then there are isomers.  Example 15: Isomers of propanol Propan-1-ol CH3CH2CH2OH Propan-2-ol CH3CH(OH)CH3 Propan-3-ol does not exist as it is named propan-1-ol, counting from the right end gets a lower number, propan-1-ol. The rest of Topic 14 gives details of the individual functional groups in organic chemistry. 234

NES/Chemistry/IGCSE 14.4 Alkanes This is a homologous series of saturated hydrocarbons with the general formula CnH2n+2 Alkanes are found in the fractions of petroleum. The carbon chain length ranges from CH4 in refinery gas to C70H142 in bitumen. The first 4 alkanes are gases at room temperature: Name Methane Ethane Propane Butane Molecular CH4 C2H6 C3H8 C4H10 formula H HH HHH HHHH Display formula H C H H C C HH C C C H H C C C C H H HH HHH HHHH Structural CH4 CH3CH3 CH3CH2CH3 CH3CH2CH2CH3 formula 16 30 44 58 Mr Notice that each successive alkane has an increase in molecular mass by 14. This is because the molecules get bigger by a CH2 each time. Alkanes are described as saturated because all the bonds between carbon atoms are single bonds. Every available space is filled (with hydrogen atoms). Chemical Properties of Alkanes Alkanes are quite unreactive. Types of reaction: 1. Combustion 2. Substitution 235

NES/Chemistry/IGCSE 1. Combustion Like all hydrocarbons, alkanes burn in excess oxygen to produce carbon dioxide and water. Type Of Reaction Combustion General Equation alkane + oxygen  carbon dioxide + water Conditions ignite in air / oxygen Example 16 C3H8 + 5O2  3CO2 + 4H2O If the supply of oxygen is limited, then incomplete combustion occurs. This results in carbon monoxide and even carbon (black solid) being formed as well. 2. Substitution with Halogens A substitution reaction is one where an atom or group of atoms in one molecule is replaced by another atom or group of atoms. At the end there are two products. An alkane can react with fluorine, chlorine, bromine, or iodine. One hydrogen atom leaves and one halogen atom joins. A hydrogen halide will also be made. Type Of Reaction Substitution General Equation alkane + halogen  halogenoalkane + hydrogen halide Conditions UV light Example 17 CH4 + Cl2  CH3Cl + HCl The substitution is quite random and the chlorine can join at any position. It is also possible for a second, third, and subsequent substitutions to happen if more halogen is added. So in example 17 it would be possible to produce CCl4 and 4 lots of HCl as well. 236

NES/Chemistry/IGCSE 14.5 Alkenes This is a homologous series of unsaturated hydrocarbons with the general formula CnH2n. They take part in addition reactions and have the functional group C=C. Alkenes are made from alkanes by the catalytic cracking of petroleum fractions. Manufacture of alkenes Catalytic cracking is the decomposition of longer alkanes to form alkenes as well as shorter alkanes and possibly hydrogen also, using a catalyst of Al2O3 and a temperature of 500oC.  Example 18: the catalytic cracking of decane C10H22  C8H18 + C2H4 alkane alkene  Example 19: the catalytic cracking of ethane C2H6  C2H4 + H2 alkene hydrogen Shorter chain alkanes make better fuels, alkenes can be used to make addition polymers and hydrogen can be used as a fuel. The first 3 alkenes are gases at room temperature: Name Ethene Propene Butene C2H4 C3H6 Molecular But-1-ene But-2-ene formula C4H8 C4H8 Display HH H HHH HH H formula H HH C C C H C C C C HH C C C C H Structural CC formula H HH H Mr HH H HH H CH2=CH2 CH2=CHCH3 CH2=CHCH2CH3 CH3CH=CHCH3 28 42 56 56 237

NES/Chemistry/IGCSE Alkanes have at least 1 double bond between carbon atoms (C=C) so there are 2 less hydrogen atoms when compared to an alkane. Alkenes are described as unsaturated as they have a double bond, between carbon atoms, and not every space is filled (with hydrogen atoms). But-1-ene and but-2-ene are structural isomers of butene. The carbon/carbon double bond is in a different position in but-1-ene and but-2-ene. Chemical Properties of Alkenes Alkenes are more reactive due to the presence of the carbon-carbon double bond. Types of reaction: 1. Combustion 2. Addition 3. Addition Polymerisation 1. Combustion Like all hydrocarbons, alkanes burn in excess oxygen to produce carbon dioxide and water. Type Of Reaction Combustion General Equation alkene + oxygen  carbon dioxide + water Conditions ignite in air / oxygen Example 20 C2H4 + 3O2  2CO2 + 2H2O 238

NES/Chemistry/IGCSE 2. Addition An addition reaction is where 2 molecules react to form a single product There are four addition reactions for alkenes: a. hydrogen b. halogen c. hydrogen halide d. steam a. Hydrogen Type Of Reaction Addition/Hydrogenation General Equation alkene + hydrogen  alkane Conditions 180oC and Ni catalyst Example 21 C2H4 + H2  C2H6 b. Halogen Type Of Reaction Addition/Halogenation General Equation alkene + halogen  dihalogenoalkane Conditions none Example 22 CH3CH=CH2 + Br2  CH3CHBrCH2Br Notice that both halogens add to the adjacent carbons that had the double bond. This is different to the substitution reaction of alkanes. Test for alkene / unsaturation Test: Add bromine water Result: orange/brown to colourless 239

NES/Chemistry/IGCSE c. Hydrogen Halide Type Of Reaction Addition General Equation alkene + hydrogen halide  halogenoalkane Conditions none Example 23 CH3CH=CH2 + HBr  CH3CHBrCH3 d. Steam Type Of Reaction Addition General Equation alkene + steam  alcohol Conditions phosphoric(V) acid catalyst 300oC Example 24 60 atmospheres pressure CH3CH=CHCH3 + H2O  CH3CH(OH)CH2CH3 240

NES/Chemistry/IGCSE 3. Addition Polymerisation A monomer is a small molecule which can be chemically bonded to other molecules to form a long chained molecule called a polymer A polymer is a long chained molecule made up of small repeating molecules which have been chemically bonded together Polymerisation is the formation of successive links between small units called monomer molecules to form a long chained macromolecule (polymer) There are two types of polymerisation: 1. Addition Polymerisation 2. Condensation Polymerisation (see Topic 14.8) Addition polymerisation is the formation of successive links between small units called monomer molecules containing a C=C double bond to form a long chained macromolecule (polymer). Conditions: High temperature high pressure Oxygen initiator  Example 25: making polyethene from ethene ethene  poly(ethene) n(CH2=CH2)  HH CC H Hn One bond in the double bond is broken. The molecule then reacts with other monomer (ethene in this example) forming a chain that is thousands of carbons long. Note - the value for n is never given 241

NES/Chemistry/IGCSE 1. Addition Polymers Name of Monomer Diagram Polymer Diagram Name of the Polymer Monomer Ethene HH HH poly(ethene) CC CC H Hn HH Propene HH HH poly(propene) But-1-ene H CC poly(but-1-ene) H CH3 n CCCH H HH CC H H C2H5 n HHH H CCCCH H HH HH H H CH3 CC But-2-ene HCCCCH CH3H n poly(but-2-ene) H HH HH poly(chloroethene) CC poly(vinyl chloride) Chloroethene HH H Cl n (vinyl chloride) CC (P.V.C.) H Cl Tetrafluoroethene FF FF poly(tetrafluoroethene) CC CC (P.T.F.E.) F Fn FF poly(phenylethene) HH Phenylethene HH CC CC H C6H5 n H C6H5 242

NES/Chemistry/IGCSE Uses of the Addition Polymers Polymer Use Poly(ethene) Poly(propene) To make plastic bags, bowls, buckets and Poly(chloroethene) packaging because it is tough and durable Poly(tetrafluoroethene) To make ropes and packaging because it is Poly(phenylethene) tough and durable Guttering and electrical insulation To make non-stick frying pans because it has a non-stick surface and it can withstand high temperatures Used in insulation and packaging 243

NES/Chemistry/IGCSE 14.6 Alcohols These are a homologous series of organic compounds with the general formula CnH2n+1OH and have the functional group –OH Alcohols are made in two ways:  The addition of steam with alkenes (see Topic 14.5)  The fermentation of sugar Fermentation of Sugar This is the anaerobic respiration of yeast with sugar. C6H12O6(aq)  2CO2(g) + 2C2H5OH(aq) It is a slow biological process. As the alcohol made is actually toxic to the yeast fermentation will stop when the alcohol content reaches about 20%. A temperature of about 35oC is used. If the temperature is about 40oC the yeast will denature and the reaction stops. If the temperature gets too low, then the rate of reaction is too slow. air lock fermentation jar glucose, water and yeast carbon dioxide gas Oxygen cannot be allowed to enter the container where the reaction is happening otherwise aerobic respiration takes place making ethanoic acid instead. C2H5OH + O2  CH3COOH + H2O 244

NES/Chemistry/IGCSE Comparison of Fermentation and Addition of Steam Fermentation Addition of Steam to Ethene 20% alcohol maximum 100% alcohol fast slow better for using in alcoholic drinks better for using as a solvent The first 4 alcohols are liquid at room temperature: Name Formula Display formula Structural formula Mr H Methanol CH3OH CH3OH 32 HCOH H Ethanol C2H5OH HH CH3CH2OH 46 HCCOH HH Propanol HHH CH3CH2CH2OH 60 (propan-1-ol) C3H7OH HCCCOH HHH Butanol HHHH 74 (butan-1-ol) C4H9OH H C C C C O H CH3CH2CH2CH2OH HHHH 245

NES/Chemistry/IGCSE Structural Isomers of Propanol Name Molecular Display Formula Structural Formula Mr Formula CH3CH2CH2OH 60 HHH Propan-1-ol C3H7OH HCCCOH HHH Propan-2-ol C3H7OH H OH H CH3CH(OH)CH3 60 HCCCH HHH Structural Isomers of Butanol Name Molecular Display Formula Structural Formula Mr Butan-1-ol Formula 74 HHHH C4H9OH H C C C C O H CH3CH2CH2CH2OH HHHH Butan-2-ol C4H9OH H OH H H CH3CH(OH)CH2CH3 74 HCCCCH HHHH 2-methylpropan-1-ol C4H9OH H CH3H CH3CH(CH3)CH2OH 74 HCCCOH HHH 2-methylpropan-2-ol C4H9OH H CH3H CH3C(OH)(CH3)CH3 74 HCCCH H OH H 246

NES/Chemistry/IGCSE Chemical Properties of Alcohols Types of reaction: 1. Combustion 2. Oxidation 3. Esterification (see Topic 14.7) 1. Combustion Alcohols burn in excess oxygen to produce carbon dioxide and water. If the alcohol is pure it will burn with a blue flame. If the alcohol is impure it will burn with a yellow flame. Type Of Reaction Combustion General Equation alcohol + oxygen  carbon dioxide + water Conditions ignite in air / oxygen Example 26 C2H5OH + 3O2  2CO2 + 3H2O 2. Oxidation Alcohols can react with oxygen, oxidising agents (or air slowly) to produce carboxylic acids and water. There is no flame in this reaction. Type Of Reaction Oxidation General Equation alcohol + oxygen  carboxylic acid + water Conditions none Example 27 C2H5OH + 2[O]  CH3COOH + H2O The [O] is used to show that the oxygen has come from an oxidising agent (including oxygen and air). 247

NES/Chemistry/IGCSE Test for alcohols Test: oxidising agent Result: colour change Chemical Oxidising Agents Colour Change Acidified (using H2SO4) potassium dichromate(VI) From To Acidified (using H2SO4) potassium manganate(VII) orange green purple colourless 248

NES/Chemistry/IGCSE 14.7 Carboxylic Acids This is a homologous series of organic compounds with the general formula C(n-1)H2(n-1)+1COOH. Carboxylic acids are made from the oxidation of alcohols. They are all weak acids, that only partly ionise (see Topic 8.1). All carboxylic acids have the functional group -COOH, which can also be written as -CO2H. functional group O C OH The first 4 carboxylic acids are liquid at room temperature: Name Molecular Display Formula Structural Formula Mr Formula O Methanoic acid HCOOH HC HCOOH 46 OH Ethanoic acid CH3COOH CH3COOH 60 H O HCC OH H Propanoic acid C2H5COOH HH CH3CH2COOH 74 O HCCC OH HH HHH CH3CH2CH2COOH 88 O Butanoic acid C3H7COOH H C C C C OH HHH 249