The empirical formula of a compound that contains 3.96 g iron and 7.54 g chlorine has to be determined. The molar mass of iron is 55.845 g/mole and the molar mass of chlorine is 35.453 g/mole.
The empirical formula of a compound is the smallest integer ratio of the number of atoms of each element present in the compound. It does not have to be the same as the molecular formula.
3.96 g of iron has 0.0709 moles and 7.54 g of chlorine has 0.2126 moles of chlorine. The integer ratio of the amount of iron and chlorine in the compound is 0.0709/0.2126 = 0.333 which is approximately equal to 1/3. The number of atoms in a mole of any element is the same.
The empirical formula of the compound that contains 3.96 g iron and 7.54 g chlorine is equal to FeCl3.