Q.Assuming the atomic weight of a metal M to be 56, find the empirical formula of its oxide containing 70.0% of M. (Ans.: M2O3)

Percentage composition is the mass of each constituent element in a compound expressed as a percentage of the compound's total mass, found by quantitative elemental analysis (if the measured percentages fall short of 100%, the shortfall is conventionally attributed to oxygen). Converting these mass percentages to moles (dividing by each element's atomic mass) and then to the smallest possible whole-number ratio of atoms gives the empirical formula of the compound — the simplest atom ratio, which may or may not match the actual molecule. The molecular formula, by contrast, states the ACTUAL number of atoms of each element present in one real molecule, and is always a whole-number multiple of the empirical formula; it is obtained by sep …