What is the molality of a d-mannose solution prepared by dissolving 45.0 g of d-mannose, c6h12o6, in 125.9 g of water?

Molality is a unit of concentration that represents the moles of solute per kilogram of solvent. The solvent here is water.

Mass of solvent in kg = 125.9 g * 1 kg/1000 g = 0.1259 kg

The moles of d-mannose knowing that its molar mass is 180.156 g/mol,

Moles solute = 45 g * 1 mol/180.156 g = 0.2498 mol

Thus,

Molality = 0.2498/0.1259 = 1.98 m