IGCSE›Oxford AQA IGCSE Chemistry›Mind mapsCrude OilOxford AQA IGCSE Chemistry: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsWhat is it?Mixture of a very large number of compoundsFormed over millions of years from ancient organismsSource of fuels and petrochemical raw materialsHydrocarbonsMolecules of hydrogen and carbon onlyMost are saturated alkanesGeneral formula CXnHX2n+2\ce{C_nH_{2n+2}}CXnHX2n+2Only single covalent C-C bondsFirst three: methane, ethane, propaneCrude oila mixture of hydrocarbonsSeparating itFractional distillation gives useful fractionsHeat crude oil so it evaporatesColumn hotter at bottom, cooler at topFractions condense at different heightsEach fraction has similar boiling pointsChain length trendsLonger chain: boiling point increasesLonger chain: viscosity increasesLonger chain: flammability decreasesPetrol runny; bitumen thickExam tipsSeparation is by boiling point, not just heatingSay evaporation then condensation at different temperatures