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Unit 2: Nature’s Chemistry 1. A Fuel is a substance which burns giving out energy. 2. Oxygen is needed for anything to burn 3. Combustion is another name for burning Test for Oxygen - Relights a glowing splint Test for Carbon Dioxide – turns limewater milky 4. Formation of Fossil Fuels (coal, oil, gas) Coal: is formed from the remains of dead plants and trees. Layers of sediment fall on top of these, over millions of years coal forms. Oil and Gas: formed from dead Sea creatures and plants. FOSSIL FUELS ARE FINITE RESOURCES 5. Fractional Distillation of Crude Oil Crude oil is a mixture of many different substances – needs to be separated. It is separated into FRACTIONS by evaporation & condensing. A Fraction is a group of similar sized molecules which have similar boiling points 6.Differences between the fractions COLOUR FLAMMABILITY Low Boiling Fraction High Boiling Fraction Gets Darker Less Flammable 7. Fractions obtained in industry Low GASES GASOLINE (PETROL) NAPHTHA KEROSINE (PARRAFIN) DIESEL RESIDUE High EASE OF EVAPOURATION Harder to Evaporate VISCOSITY More Viscous (thicker) USES COOKING, HEATING CARS LIGHTING, HEATING TRAINS, LORRIES BITUMEN FOR TAR ON ROADS 8. Burning Hydrocarbons **HYDROCARBON + OXYGEN CARBON DIOXIDE + WATER** 9. Pollution from burning fuels CARBON MONOXIDE – Formed in limited air POISONOUS OXIDES OF NITROGEN – formed in car exhaust ACID RAIN SULPHUR DIOXIDE – formed due to sulphur impurities in certain fuels ACID RAIN UNBURNT HYDROCARBONS *** PREVENTION: Catalytic Converter (platinum) converts harmful gases into un-harmful gases. 10. Hydrocarbons are compounds formed between HYDROGEN and CARBON. HYDROCARBONS ALKANES Methane Ethane Propane Butane Pentane Hexane Heptane Octane CH4 C2H6 C3H8 C4H10 C5H12 C6H14 C7H16 C8H18 CnH2n+2 - contain only C-C single bonds ALKENES Ethene Propene Butene Pentene Hexene Heptene Octene C2H4 C3H6 C4H8 C5H10 C6H12 C7H14 C8H16 CnH2n - contain C=C double bonds UNSATURATED SATURATED CYCLOALKANES Cyclopropane Cyclobutane Cyclopentane Cyclohexane Cycloheptane Cyclooctane C3H6 C4H8 C5H10 C6H12 C7H14 C8H16 CnH2n - All C’s joined in a circle SATURATED 11.TEST FOR UNSATURATION ( C= C ) -UNSATURATED hydrocarbons rapidly decolourise bromine solution 12. Full Shortened Structural Formula e.g. H H H H H C C C C H H H H H CH3CH2CH2CH3 FULL STRUCTURAL FORMULA C4H10 SHORTENED STRUCTURAL FORMULA MOLECULAR FORMULA 13.Homologous Series Alkanes, alkenes, and cycloalkanes are examples of HOMOLOGOUS SERIES. In a homologous series: (a) members represented by GENERAL FORMULA (b) as the molecules get bigger, the melting and boiling points increase (c) members have similar chemical properties 14. Isomers – compounds which have same formula but different structure e.g. H H H H H C C C C H H H H H H H H H C C C H H H C H H H Isomers have different properties eg. different melting and boiling points. 15.Naming Branched Alkanes - name longest carbon chain -> hexane - number longest carbon chain to give lowest numbers to carbons with branches attached - name branches -CH3 methyl -CH2CH3 ethyl -if more than one of same branch use prefix di ( if two ) tri ( if three ) - name branched alkane 2,3-dimethylhexane 16.Naming Branched Alkenes - find longest carbon chain containing double bond number this carbon chain to give lowest number to where double bond starts -> pent-2-ene indentify branches and indicate position with number in front of branch name 4-methylpent-2-ene 17.Addition Reactions Alkenes undergo ADDITION REACTIONS with hydrogen, halogens, and water e.g. H H C C H H + Br2 Br H H C C H H Br 18.Cracking Breaking long chain molecules into smaller, more useful molecules. + Catalyst needed (aluminium oxide) e.g. C10H22 C2H4 + C8H18 Cracking produces a mixture of UNSATURATED and SATURATED molecules. 19. Alcohols ( alkanols ) contain -OH functional group (called HYDROXYL GROUP ) + ethanol Alcohols are used as SOLVENTS and FUELS. 20. Carboxylic Acids ( alkanoic acids ) - contain CARBOXYL group eg. Vinegar is a solution of ethanoic acid. It is used as a food preservative and in household cleaning products. 21. Esters Esters are formed when a CARBOXYLIC ACID reacts with an ALCOHOL. This is a CONDENSATION reaction. Some uses PERFUMES. of esters include FLAVOURINGS, SOLVENTS, and these are compounds containing CARBON, OXYGEN plants are a source of carbohydrates carbohydrates are used as food or fuels HYDROGEN, and 22. Carbohydrates - Carbohydrates are grouped according to their size: MONOSACCHARIDES C6H12O6 e.g. glucose, fructose DISACCHARIDES C12H22O11 e.g. sucrose, maltose POLYSACCHARIDES (C6H10O5)n e.g. starch Testing for starch: turns Iodine Blue/ Black Benedict’s Test: Turns blue orange/ brown with all sugars ending in ‘OSE’ except SUCROSE Condensation Polymerisation Starch is formed by joining many glucose molecules together: 3 Glucose Monomers H 2O Part of Starch Polymer HYDROLYSIS Breaking down large molecules into smaller ones using water. e.g. Starch + Water Glucose (C6H10O5)n + H2O nC6H12O6 Alcohol - produced by FERMENTATION of glucose - YEAST (contains enzymes) is needed - Ethanol is the alcohol formed Glucose Yeast Ethanol + Carbon dioxide Increasing the alcohol content - by DISTILLATION (evaporate and condense) - can only get ~15% alcohol by fermentation (alcohol kills enzymes in yeast) - ethanol boils at 79oC, water boils at 100oC 23. Calculations from Balanced Equations -allows us to work out the mass of a product formed when the mass of reactant is known eg. Calculate the mass of MgSO4 produced when 4.9g of magnesium reacts with excess sulphuric acid Mg + 1mol 24.5g H2SO4 1g 4.9g MgSO4 1mol 120.5g + H2 MgSO 4 120.5g 24.5 120.5 x 4.9 g 24.5 = 24.1g 24. Energy from Fuels Alkanes and alcohols can be used as fuels since they burn well. Combustion is an EXOTHERMIC reaction. In an exothermic reaction the products have less energy than the reactants. The amount of energy released by a fuel when it burns can be worked out using: Eh = cm∆T c = 4.18 (specific heat capacity of water) m = mass of water (in kg) ∆T= change in temperature (oC)