AQA GCSE Chemistry- Organic Chemistry PDF

AQA​ ​GCSE​ ​Chemistry Topic​ ​7:​ ​Organic​ ​chemistry Carbon​ ​compounds​ ​as​ ​fuels​ ​and​ ​feedstock Notes (Content​ ​in​ ​bold​ ​is​ ​for​ ​Higher​ ​Tier​ ​only) www.pmt.education Crude​ ​oil,​ ​hydrocarbons​ ​and​ ​alkanes Crude​ ​oil: I...

AQA​ ​GCSE​ ​Chemistry Topic​ ​7:​ ​Organic​ ​chemistry Carbon​ ​compounds​ ​as​ ​fuels​ ​and​ ​feedstock Notes (Content​ ​in​ ​bold​ ​is​ ​for​ ​Higher​ ​Tier​ ​only) www.pmt.education Crude​ ​oil,​ ​hydrocarbons​ ​and​ ​alkanes Crude​ ​oil: Is​ ​a​ ​finite​ ​resource​ ​found​ ​in​ ​rocks Is​ ​the​ ​remains​ ​of​ ​an​ ​ancient​ ​biomass​ ​consisting​ ​mainly​ ​of​ ​plankton that​ ​was​ ​buried​ ​in​ ​mud Is​ ​a​ ​mixture​ ​of​ ​a​ ​very​ ​large​ ​number​ ​of​ ​compounds o Mixture:​ ​2​ ​or​ ​more​ ​elements​ ​that​ ​are​ ​not​ ​chemically​ ​combined o The​ ​chemical​ ​properties​ ​of​ ​each​ ​substance​ ​in​ ​the​ ​mixture​ ​are unchanged It​ ​is​ ​possible​ ​to​ ​separate​ ​the​ ​substances​ ​in​ ​the​ ​mixture​ ​by​ ​physical methods​ ​including​ ​distillation Most​ ​of​ ​the​ ​compounds​ ​in​ ​crude​ ​oil​ ​consist​ ​of​ ​molecules​ ​made​ ​up​ ​of hydrogen​ ​and​ ​carbon​ ​only​​ ​(hydrocarbons).​ ​Most​ ​of​ ​these​ ​saturated hydrocarbons​ ​are​ ​alkanes. Hydrocarbons: have​ ​the​ ​general​ ​formula:​ ​Cn​​ H​2n+2 Alkane​ ​molecules​ ​can​ ​be​ ​represented​ ​in​ ​the​ ​following​ ​forms: The​ ​first​ ​4​ ​alkanes​ ​are​ ​methane,​ ​ethane,​ ​propane​ ​and​ ​butane​ ​(MEPB: Monkeys​ ​Eat​ ​Peanut​ ​Butter) Fractional​ ​distillation​ ​and​ ​petrochemicals The​ ​oil​ ​is​ ​heated​ ​in​ ​the​ ​fractionating​ ​column​ ​and​ ​the​ ​oil​ ​evaporates and​ ​condenses​ ​at​ ​a​ ​number​ ​of​ ​different​ ​temperatures. The​ ​many​ ​hydrocarbons​ ​in​ ​crude​ ​oil​ ​can​ ​be​ ​separated​ ​into​ ​fractions each​ ​of​ ​which​ ​contains​ ​molecules​ ​with​ ​a​ ​similar​ ​number​ ​of​ ​carbon atoms The​ ​fractionating​ ​column​ ​works​ ​continuously,​ ​heated​ ​crude​ ​oil​ ​is piped​ ​in​ ​at​ ​the​ ​bottom.​ ​The​ ​vaporised​ ​oil​ ​evaporates​ ​and​ ​rises​ ​up​ ​the column​ ​and​ ​the​ ​various​ ​fractions​ ​are​ ​constantly​ ​tapped​ ​off​ ​at​ ​the different​ ​levels​ ​where​ ​they​ ​condense. www.pmt.education  The​ ​fractions​ ​can​ ​be​ ​processed​ ​to​ ​produce​ ​fuels​ ​and​ ​feedstock​ ​for the​ ​petrochemical​ ​industry. ○ Many​ ​of​ ​the​ ​fuels​ ​on​ ​which​ ​we​ ​depend​ ​for​ ​our​ ​modern lifestyle,​ ​such​ ​as​ ​petrol,​ ​diesel​ ​oil,​ ​kerosene,​ ​heavy​ ​fuel​ ​oil​ ​and liquefied​ ​petroleum​ ​gases,​ ​are​ ​produced​ ​from​ ​crude​ ​oil. ○ Many​ ​useful​ ​materials​ ​on​ ​which​ ​modern​ ​life​ ​depends​ ​are produced​ ​by​ ​the​ ​petrochemical​ ​industry,​ ​such​ ​as​ ​solvents, lubricants,​ ​polymers,​ ​and​ ​detergents. ○ The​ ​vast​ ​array​ ​of​ ​natural​ ​and​ ​synthetic​ ​carbon​ ​compounds occur​ ​due​ ​to​ ​the​ ​ability​ ​of​ ​carbon​ ​atoms​ ​to​ ​form​ ​families​ ​of similar​ ​compounds. Properties​ ​of​ ​hydrocarbons Some​ ​properties​ ​of​ ​hydrocarbons​ ​depend​ ​on​ ​the​ ​size​ ​of​ ​their molecules.​ ​These​ ​properties​ ​influence​ ​their​ ​use​ ​as​ ​fuels. Shorter​ ​the​ ​molecules,​ ​the​ ​less​ ​viscous​ ​it​ ​is.​ ​(more​ ​runny) The​ ​longer​ ​the​ ​molecules,​ ​the​ ​more​ ​viscous​ ​it​ ​is. The​ ​shorter​ ​the​ ​molecules,​ ​the​ ​lower​ ​the​ ​temperature​ ​at​ ​which​ ​that fraction​ ​is​ ​vaporised​ ​or​ ​condensed​ ​–​ ​and​ ​the​ ​lower​ ​its​ ​boiling​ ​point. The​ ​shorter​ ​the​ ​molecules,​ ​the​ ​more​ ​flammable​ ​it​ ​is. Hydrocarbons​ ​are​ ​burnt​ ​so​ ​that​ ​they​ ​can​ ​be​ ​used​ ​as​ ​fuel,​ ​since​ ​the reaction​ ​produces​ ​energy. o ​ ​hydrocarbon​ ​->​ ​carbon​ ​dioxide​ ​+​ ​water o the​ ​hydrogen​ ​and​ ​carbon​ ​are​ ​oxidised​ ​in​ ​the​ ​reaction Cracking​ ​and​ ​alkenes Hydrocarbons​ ​can​ ​be​ ​cracked​ ​to​ ​produce​ ​smaller,​ ​more​ ​useful molecules.​ ​This​ ​process​ ​involved​ ​heating​ ​the​ ​hydrocarbons​ ​to vaporise​ ​them. The​ ​processes​ ​are: o Passing​ ​them​ ​over​ ​a​ ​hot​ ​catalyst​ ​(catalytic​ ​cracking) o OR​ ​mixing​ ​them​ ​with​ ​steam​ ​and​ ​heated​ ​to​ ​a​ ​very​ ​high temperature​ ​so​ ​that​ ​thermal​ ​decomposition​ ​reactions​ ​can occur​ ​(steam​ ​cracking) alkenes: o The​ ​products​ ​of​ ​cracking​ ​include​ ​alkanes​ ​and​ ​unsaturated hydrocarbons​ ​called​ ​alkenes.​ ​Alkenes​ ​have​ ​the​ ​general​ ​formula C​n​H​2n​​ ​and​ ​have​ ​at​ ​least​ ​one​ ​double​ ​carbon-carbon​ ​bond. www.pmt.education  o The​ ​first​ ​2​ ​alkenes​ ​are​ ​ethene​ ​and​ ​propene. o Unsaturated​ ​carbons​ ​can​ ​be​ ​represented​ ​in​ ​the​ ​following forms: o o Alkenes​ ​react​ ​with​ ​bromine​ ​water,​ ​turning​ ​it​ ​from​ ​orange​ ​to colourless,​ ​alkanes​ ​do​ ​not​ ​(this​ ​is​ ​because​ ​an​ ​alkene’s​ ​double bond​ ​makes​ ​them​ ​more​ ​reactive​ ​than​ ​alkanes) o Alkenes​ ​are​ ​used​ ​for​ ​producing​ ​other​ ​chemicals​ ​(e.g.​ ​polymers) Some​ ​of​ ​the​ ​products​ ​made​ ​from​ ​cracking​ ​are​ ​useful​ ​as​ ​fuels,​ ​since they​ ​have​ ​shorter​ ​chains​ ​than​ ​the​ ​alkanes​ ​you​ ​started​ ​with,​ ​making them​ ​more​ ​flammable​ ​so​ ​a​ ​better​ ​fuel Equations​ ​for​ ​cracking: o you​ ​must​ ​make​ ​sure​ ​there​ ​are​ ​the​ ​same​ ​number​ ​of​ ​carbons and​ ​hydrogens​ ​on​ ​each​ ​side​ ​of​ ​the​ ​equation​ ​(the​ ​same​ ​as​ ​any other​ ​reaction) o remember​ ​you​ ​are​ ​going​ ​from​ ​a​ ​bigger​ ​molecule​ ​to​ ​usually​ ​2 smaller​ ​molecules o e.g.​ ​if​ ​you​ ​had​ ​to​ ​add​ ​the​ ​other​ ​product​ ​to​ ​this​ ​reaction equation:​ ​C6​​ H​14​ →​ ​ ​C2​​ H​4​​ ​+​ ​?,​ ​you​ ​simply​ ​calculate​ ​how​ ​many carbons​ ​and​ ​hydrogens​ ​are​ ​left​ ​over. carbons:​ ​6-2=4 hydrogens:​ ​14-4=10 therefore,​ ​?=​ ​C4​​ H​10 www.pmt.education