The boiling point of diethyl ether, CH3CH2OCH2CH3, is 34.500 °C at 1 atmosphere. Kb(diethyl ether) = 2.02 °C/m
In a laboratory experiment, students synthesized a new compound and found that when 13.85 grams of the compound were dissolved in 283.2 grams of diethyl ether, the solution began to boil at 34.843 °C. The compound was also found to be nonvolatile and a non-electrolyte.
What is the molecular weight they determined for this compound ?
delta T = Kb*molality
Substitute and solve for m
m = mols/kg solvent
Substitute and solve for mols.
mols = grams/molar mass. You know grams and mols, solve for molar mass.
To determine the molecular weight of the compound, we can use the formula:
Molecular weight = (mass of solute / moles of solute)
First, we need to calculate the moles of the solvent (diethyl ether) using the boiling point elevation formula:
ΔTb = Kb * m
Where:
ΔTb is the boiling point elevation (34.843 °C - 34.500 °C = 0.343 °C)
Kb is the molal boiling point elevation constant (2.02 °C/m)
m is the molality (moles of solute / mass of solvent in kg)
Rearranging the formula, we can solve for m:
m = ΔTb / Kb
Substituting the given values, we have:
m = 0.343 °C / 2.02 °C/m = 0.17 m
Next, we need to calculate the moles of the solute (compound):
moles = m * mass of solvent (in kg)
= 0.17 m * (283.2 g / 1000 g/kg)
≈ 0.048 mol
Finally, we can determine the molecular weight:
Molecular weight = mass of solute / moles of solute
= 13.85 g / 0.048 mol
≈ 288.5 g/mol
Therefore, the molecular weight determined for this compound is approximately 288.5 g/mol.