What is the molality of a solution made by dissolving 9.0 g of calcium chloride dihydrate in 40.0 g of water?

Answer is: molality of calcium chloride solution is 2.025 m.

m(CaCl₂) = 9.0 g.
n(CaCl₂) = m(CaCl₂) ÷ M(CaCl₂).
n(CaCl₂) = 9 g ÷ 111 g/mol.
n(CaCl₂) = 0.081 mol; amount of substance.
m(H₂O) = 40.0 g ÷ 1000 g/kg = 0.04 kg.
b(solution) = n(CaCl₂) ÷ m(H₂O).
b(solution) = 0.081 mol ÷ 0.04 kg.
b(solution) = 2.025 mol/kg.