IGCSE›Cambridge IGCSE Chemistry›Mind mapsFormulaeCambridge IGCSE Chemistry: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsTwo formulaeMolecular: actual atoms in one moleculeEmpirical: simplest whole-number ratioGlucose CX6HX12OX6\ce{C6H12O6}CX6HX12OX6 → empirical CHX2O\ce{CH2O}CHX2OMolecular = multiple of empiricalIonic formulaePositive and negative charges must balanceMgX2+\ce{Mg^2+}MgX2+ and OX2−\ce{O^2-}OX2− give MgOCaX2+\ce{Ca^2+}CaX2+ needs two ClX−\ce{Cl-}ClX−: CaClX2\ce{CaCl2}CaClX2BalancingSame atoms of each element both sidesChange coefficients, never the formulae2 Mg+OX2→2 MgO\ce{2Mg + O2 -> 2MgO}2Mg+OX22MgOState symbols: (s), (l), (g), (aq)Formulaeand equationsH₂O(aq)Ionic equationsShow only ions that reactCancel spectator ionsHX+(aq)+OHX−(aq)→HX2O(l)\ce{H+(aq) + OH-(aq) -> H2O(l)}HX+(aq)+OHX−(aq)HX2O(l)NaX+\ce{Na+}NaX+ and ClX−\ce{Cl-}ClX− are spectators hereDeducing equationsAcid + base → salt + waterFuel + oxygen → COX2\ce{CO2}COX2 + waterNaX2COX3+2 HCl→2 NaCl+COX2+HX2O\ce{Na2CO3 + 2HCl -> 2NaCl + CO2 + H2O}NaX2COX3+2HCl2NaCl+COX2+HX2OExam tipsEmpirical CH, Mr 78: divide by 13 → CX6HX6\ce{C6H6}CX6HX6Show full equation, then cancel spectators