What is the molecular weight of sulfur if 35.5 grams of sulfur dissolve in 100.0 grams of CS2 to produce a solution that has a boiling point of 49.48°C?
The molecular mass of sulfur is 256 u.
As you might have guessed, this is a boiling point elevation problem. The formula for boiling point elevation is
We need to look up the values of
We can use this information to calculate the molality
We have 100.0 g or 0.1000 kg of CS₂. So we can calculate the moles of sulfur.
Moles of solute = molality× kilograms of solvent = 1.38 mol·kg⁻¹ × 0.1000 kg = 0.138 mol
So 35.5 g of sulfur = 0.138 mol
∴ Molar mass of sulfur =
∴ The experimental molecular mass of sulfur is 257 u (The actual molecular mass of S₈ is 256 u).