Final answer:
To find an empirical formula, one must have the mass or percentage of elements, convert these to moles, then simplify the mole ratios to the smallest whole numbers. Examples include methanol (CH3O) from its percent composition, and NO2 from given masses of nitrogen and oxygen.
Step-by-step explanation:
The empirical formula of a compound is the simplest whole-number ratio of the elements within that compound. To determine an empirical formula, you would normally need the mass of each element present in the sample. A common technique involves converting these masses to moles, dividing each by the smallest number of moles to get the ratio, and then deriving the empirical formula from this ratio.
For instance, given a compound containing 40.0% C, 6.71% H, and 53.28% O, you would calculate the moles of each element, based on a hypothetical 100-gram sample, then simplify the ratios of moles to find that the empirical formula is CH₃O - generally recognized as methanol or wood alcohol. In another case, if a compound contains 0.130 g of nitrogen and 0.370 g of oxygen, through similar steps, its empirical formula would be NO₂.
If you know only the percent composition of carbon in a compound (like 92.3% C) and its molar mass (78.1 g/mol), you could determine its molecular formula, which could be a multiple of its empirical formula, by comparing the molar mass of the empirical formula to the given molar mass of the compound.