GCSE›AQA GCSE Chemistry›Mind mapsRelative Masses and MolesAQA GCSE Chemistry: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsFormula massMr = sum of Ar of all atoms in formulaMultiply Ar by number of each atomCOX2\ce{CO2}COX2: 12 + 16 × 2 = 44HX2O\ce{H2O}HX2O: (1 × 2) + 16 = 18The moleUnit for amount of substance1 mole has mass in g equal to its MrAvogadro constant: 6.02×10236.02\times10^{23}6.02×1023 per mole1 mol COX2\ce{CO2}COX2 = 44 gMolesrelative masses and molesMrmolgMass and molesmoles=massMr\text{moles} = \frac{\text{mass}}{M_r}moles=Mrmassmass=moles×Mr\text{mass} = \text{moles}\times M_rmass=moles×Mr22 g COX2\ce{CO2}COX2 → 22 ÷ 44 = 0.5 molUsing equationsBalancing numbers give the mole ratio Convert given mass to moles Use ratio to find moles wanted Convert moles to mass Masses to moles gives whole number ratio to balanceExam tipsMoles are the bridge between massesCannot convert masses directly using equation numbers