Question

Given that the density of water is 0.975 g/ml and that 171 g of sucrose (molar mass: 342.30 g/mol) is dissolved in 512.85 ml of water at 80°c, what is the molality of this solution? use . 0.325 m 0.333 m 0.975 m 1.00 m

Answer 1

Molality is defined as the number of moles of solute in 1 kg of solvent .
the mass of water - 512.85 ml x 0.975 g/ml = 500 g
number of moles of solute in 500 g of water - 171 g / 342.30 g/mol = 0.500 mol
the number of sucrose moles in 500 g of water - 0.500 mol
therefore number of sucrose moles in 1 kg water - 0.500 mol / 0.500 kg = 1.00 
molality of solution - 1.00 M