Final answer:
To determine an empirical formula, convert the percent composition of each element to moles, then divide by the smallest number of moles to find the whole number ratio, which gives the empirical formula.
Step-by-step explanation:
To find the empirical formula of a compound, you need to know the percent composition of each element in the compound. Once you have this, you convert the percentages to grams (assuming a 100 g sample), then convert the mass of each element to moles by using the atomic masses from the periodic table. Afterward, you will divide each of the mole values by the smallest mole value obtained to get a whole number ratio. If the ratios are not whole numbers, they may be multiplied by a common factor to achieve whole numbers, as the empirical formula should have subscripts that are whole numbers.
Example: If a compound contains 40.0% carbon, 6.71% hydrogen, and 53.28% oxygen, its empirical formula can be determined by converting these percentages to moles, which for carbon would be 40.0 g C × (1 mol C / 12.01 g C), for hydrogen 6.71 g H × (1 mol H / 1.008 g H), and for oxygen 53.28 g O × (1 mol O / 16.00 g O). The resulting molar ratios are then simplified to find the empirical formula.
The empirical formula for a hypothetical compound with a composition of 69.94% iron and 30.06% oxygen would be Fe2O3 after converting iron and oxygen percentages to moles and finding the smallest whole number ratio.
For a sample containing 0.130 g of nitrogen and 0.370 g of oxygen, the empirical formula is found by converting these masses to moles and simplifying the ratio, resulting in NO2 as the empirical formula.