The empirical formula of a compound represents the simplest whole-number ratio of its constituent elements. To find the empirical formula, we first need to convert the percent composition by mass to moles. Then, divide each mole value by the smallest mole value to find the mole ratios. Finally, use these mole ratios to write the empirical formula.
Convert percent composition to moles:
Boron: 78.14 g/100 g * 1 mol/10.81 g = 7.22 moles
Hydrogen: 21.86 g/100 g * 1 mol/1.01 g = 21.70 moles
Find the mole ratios:
Boron: 7.22 moles / 7.22 moles = 1
Hydrogen: 21.70 moles / 7.22 moles = 3
Write the empirical formula:
Boron: 1 B
Hydrogen: 3 H
The empirical formula of the compound is BH3.