To determine the formula mass of beryllium chloride, BeCl₂, we start up with the basis of one mole first.
Basis: 1 mole BeCl₂
To determine the molar mass of BeCl₂, we add up the mass of one mole of beryllium and two moles of chlorine.
1 mol Be = 9 g/mol
1 mol of Cl = 35.45 g/mol
Solving,
molar mass of BeCl₂ = (1 mol Be)(9 g/mol) + (2 mols Cl)(35.45 g/mol)
molar mass of BeCl₂ = 79.9 g
Then, we take into consideration that 1 mol is equal to 6.022 x 10²³ formula units.
formula mass BeCl₂ = (79.9 g/mol)(1 mol/6.022 x 10²³ formula units)
formula mass of BeCl₂ = 1.33 x 10⁻²² g/formula unit
Answer: 1.33 x 10⁻²² g/formula unit