Molal Boiling-Point-Elevation Constant for CS2
Explanation:
To solve this problem we need to use the boiling-point elevation formula:
Tsolution - Tpure solvent = Kb * m
Where Tsolution and Tpure solvent are the boiling point of the CSâ solution (47.52 °C) and of pure CSâ (46.3 °C), respectively. Kb is the constant asked by the problem, and m is the molality of the solution.
So in order to use that equation and solve for Kb, first we calculate the molality of the solution.
molality = mol solute / kg solvent
Density of CSâ = 1.26 g/cm³
Mass of 410.0 mL of CSâ â 410 cm³ * 1.26 g/cm³ = 516.6 g = 0.5166 kg
molality = 0.270 mol / 0.5166 kg = 0.5226 m
Now we solve for Kb:
Tsolution - Tpure solvent = Kb * m
47.52 °C - 46.3 °C = Kb * 0.5226 m
Kb = 0.428 m/°C