Question

A 4.00 g sugar cube (sucrose: C12H22O11) is dissolved in a 350 mL teapot containing 80∘ C water (density of water at 80∘ C= 0.975 g/mL). What is the molality of the sugar solution? Express the molality with the appropriate units.

Answer 1

mass of solute = 4.00 g
molar mass of solute (C12H22O11) = 12*12 + 22*1 + 11*16 = 342 g/mol
number of moles of solute = mass/molar mass
= 4.00/342
= 0.0117 mol

volume of water = 350 mL
SInce density of water = 0.975g/mL, mass of water = 350 *0.975 = 341.25g
mass of solvent = 341.25 g = 0.34125 kg

molality = number of moles of solute / mass of solvent in kg
= 0.0117 mol / 0.34125 kg
= 0.0343 m