Answer:
Molality = 18.5 m
Explanation:
Let's analyse data. We want to determine molality which means mol of solute / 1kg of solvent. (Hence we need, the moles of solute and the mass of solvent in kg)
12.83 M means molarity → mol of solute in 1L of solution
Density refers always to solution → Mass of solution / Volume of solution
1L = 1000 mL
We can determine the mass of solution with density
0.9102 g/mL = Mass of solution / 1000 mL
Mass of solution = 0.9102 g/mL . 1000 mL → 910.2 g
Let's convert the moles of solute (NH₃) to mass
12.83 mol . 17.03 g/ 1 mol = 218.5 g
We can apply this knowledge:
Mass of solution = Mass of solvent + Mass of solute
910.2 g = Mass of solvent + 218.5 g
910.2 g - 218.5 g = 691.7 g → Mass of solvent.
Let's convert the mass in g to kg
691.7 g . 1kg / 1000 g = 0.6917kg
We can determine molalilty now → 12.83 mol / 0.6917kg
Molality = 18.5 m
