The empirical formula is Fe₃O₄.
The empirical formula is the simplest whole-number ratio of atoms in a compound.
The ratio of atoms is the same as the ratio of moles, so our job is to calculate the molar ratio of Fe to O.
I like to summarize the calculations in a table.
Element Moles Ratio¹ ×3² Integers³
Fe 0.77 1 3 3
O 1.0 1.3 3.9 4
¹ To get the molar ratio, you divide each number of moles by the smallest number (0.77).
² If the ratio is not close to an integer, multiply by a number (in this case, 3) to get numbers that are close to integers.
³ Round off these numbers to integers (3 and 4).
The empirical formula is Fe₃O₄.
