Why do we use moles when calculating empirical chemical formulas, but not the mass?

The valence of aluminum is +3, and the valence of the chlorine is -1. the formula fir the aluminum chloride is correctly written as

Which of the following is most likely true about water in chemical systems? a) water dissolves nonpolar ionic compounds. b) water dissociates ionic compounds. c) water dissociates covalent molecules. d) water dissolves nonpolar covalent substances.

Identify the lewis base in this balanced equation: fe3+ h2o fe(h2o)63+