What is the molality of a solution containing 13.9 g Na2SO4 dissolved in 1796.0 g of water?

Answer 1

Molality = moles of solute (Na₂SO₄) per kg of solvent (water)

We can find the mols of Na₂SO₄ by using the mass (13.9 g) and the molar mass (142 g / mol).

moles Na₂SO₄ = 13.9 g x 1 mol / 142 g = 0.0979 mols

We can convert 1796.0 g of water to kg.

1796.0 g x 1 kg /1000 g = 1.796 kg

We now have all we need to calculate molality.

Molality = 0.0979 mols Na₂SO₄ / 1.796 kg water = 0.0545 m (3 sig. figs.)