Question

What is the approximate molar mass of a molecular solute if 300 g of the solute in 1000 g of water causes the solution to have a boiling point of 101°c? (kb = 0.512°c/m; kf = 1.86°c/m; molar mass of water = 18 g) 30 g 150 g 300 g 15 g?

Answer 1

Answer is: the approximate molar mass of a molecular solute is 150 g.
m(molecular solute) = 300 g.
m(water) = 1000 g ÷ 1000 g/kg = 1 kg.
ΔT = 101°C - 100°C = 1°C.
M(molecular solute) = Kb · m(molecular solute) / m(water) · ΔT.
M(molecular solute) = 0,512°C/m · 300 g / (1 kg · 1°C).
M(molecular solute) = 153,6 g/mol.