Answer is: empirical formula of a compound is CaCl₂.
1) Calculate amount of substance for calcium
m(Ca) = 80 g.
n(Ca) = m(Ca) ÷ M(Ca).
n(Ca) = 80 g ÷ 40.078 g/mol.
n(Ca) = 1.996 mol.
2) Calculate amount of substance of chlorine
m(Cl) = 140 g.
n(Cl) = m(Cl) ÷ M(Cl).
n(Cl) = 140 g ÷35.45 g/mol.
n(Cl) = 3.94 mol.
3) n(Ca) : n(Cl) = 1.996 mol : 3.94 mol /1.996.
n(Ca) : n(Cl) = 1 : 2; one calcium atom and two chlorine atoms.
