IGCSE›Edexcel IGCSE Chemistry›Mind maps1.2 Elements, Compounds & MixturesEdexcel IGCSE Chemistry: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsClassifyingElement: one type of atom onlyCompound: elements chemically combined, fixed ratioMixture: physically combined, no fixed ratioMixtures separate by physical methodsPurityPure substance melts at a fixed temperatureMixture melts or boils over a rangeMelting point can show impuritiesSeparatingFiltration: insoluble solid from liquidCrystallisation: dissolved solid from solutionSimple distillation: solvent from solutionFractional distillation: liquids with different boiling pointsMixtureselements and compoundsChromatographySubstances move at different rates up the paperDepends on solubility and attraction to paperOne spot splitting shows a mixtureCompare with known reference spotsRf valueRf=distance by substancedistance by solventR_f = \frac{\text{distance by substance}}{\text{distance by solvent}}Rf=distance by solventdistance by substanceSubstance 6 cm, solvent 10 cmRf=610=0.6R_f = \frac{6}{10} = 0.6Rf=106=0.6Characteristic for each substance in a solventExam tipsAir is a mixture, not a compoundSay fixed, sharp temperature for pure substancesDraw the baseline in pencil, not pen