answer and explanation
molality is defined as the mols of solute divided by the kg of solvent.
molality = mols of solute/ kg of solvent
aluminium sulfate has a molar mass of 342.15g/mol
therefore the number of mols of a 80 gram sample is
n =m/M
= 80/342.15
= 0.23 mols
the mass of water in kilograms is 0.625kg
therefor the molality is
molality = 0.23mols/0.625kg
= 0.37 mols/kg
