Final answer:
The molecular mass of the unknown nonelectrolyte compound can be calculated by first determining the molality of the solution, then finding the moles of the compound, and finally dividing the mass of the solute by the number of moles. The molecular mass is found to be approximately 148.81 g/mol.
Step-by-step explanation:
Determination of Molecular Mass from Freezing Point Depression
To determine the molecular mass of the unknown nonelectrolyte compound, we use the concept of freezing point depression. The freezing point depression formula is ΔTf = Kf * m where ΔTf is the freezing point depression, Kf is the freezing point depression constant for water (1.86°C/kg/mol), and m is the molality of the solution.
First, we need to calculate the molality (m) of the compound:
ΔTf = 2.5°C
m = ΔTf / Kf = 2.5°C / 1.86°C/kg/mol = 1.344 mol/kg
Next, we calculate the moles of the compound dissolved:
Moles = molality (m) * mass of solvent (kg) = 1.344 mol/kg * 0.025 kg = 0.0336 mol
Finally, the molecular mass (M) of the compound can be calculated by dividing the mass of the solute by the number of moles:
Mass of the compound = 5.0g
Moles of the compound = 0.0336 mol
Molecular Mass (M) = Mass / Moles = 5.0 g / 0.0336 mol = 148.81 g/mol
The molecular mass of the unknown compound is approximately 148.81 g/mol.