Kayanne M. answered • 03/18/22
Ph. D. in Chemistry with 12 years of teaching experience
Angelina,
Molality = moles of solute/kg solvent
In this example, the solute is Ca(NO3)2, and the solvent is H2O.
The given molality = 0.513 m which translates to 0.513 mols of Ca(NO3)2/ 1 kg H2O
We are given 75.9 g Ca(NO3)2 so we need to convert that using the molar mass to see how many moles of solute we have.
Mass ÷ molar mass = moles
75.9 g x 1 mol/164.09 g = 0.463 mols Ca(NO3)2
Since the given molality is 0.513 mols/kg solvent, we need to figure out what mass of solvent fits if we have 0.463 mols
0.463 mols x 1 kg solvent/0.513 mols = 0.903 kg solvent (H2O)
The answer is practical since we have fewer mols of solute, it requires less than 1 kg of solvent.
