What is the molality of sodium chloride in solution that is 13.0% by mass sodium chloride and that has a density of 1.10 g/ml?

Answer is: molality od sodium chloride is 2,55 mol/kg.

V (solution) = 100 ml.

m (solution) = d (solution) · V (solution).

m (solution) = 1,10 g/ml · 100 ml.

m (solution) = 110 g.

ω (NaCl) = 13,0% = 0,13.

m (NaCl) = ω (NaCl) · m (solution).

m (NaCl) = 0,13 · 110 g.

m (NaCl) = 14,3 g.

n (NaCl) = m (NaCl) : M (NaCl).

n (NaCl) = 14,3 g : 58,5 g/mol.

n (NaCl) = 0,244 mol.

m (H₂O) = 110 g - 14,3 g.

m (H₂O) = 95,7 g = 0,0957 kg.

b (NaCl) = n (NaCl) : m (H₂O).

b (NaCl) = 0,244 mol : 0,0957 kg.

b (NaCl) = 2,55 mol/kg.