Final answer:
To calculate the molality, convert the mass of ammonia to moles and divide by the mass of the solvent in kilograms. The molality of the solution is 3.100 mol/kg.
Step-by-step explanation:
The question asks about the molality of a solution prepared by dissolving 19.0 g of ammonia (NH3) in 450 mL of a solvent with a density of 0.80 g/mL.
First, we need to calculate the mass of the solvent. Since the density of the solvent is 0.80 g/mL, the mass of the 450 mL solvent is 360 g (450 mL × 0.80 g/mL).
Next, we convert the mass of ammonia to moles. The molar mass of NH3 is approximately 17.03 g/mol, thus 19.0 g NH3 is about 1.116 moles (19.0 g ÷ 17.03 g/mol).
Molality (m) is defined as the number of moles of solute per kilogram of solvent. So, the molality of the solution is calculated as follows:
1.116 moles NH3 / 0.360 kg solvent = 3.100 mol/kg.