solution of 0.2113 g of water dissolved in 25.0 g of a solvent freezes at 11.5°C below the freezing point of the solvent. What is Kf for this solvent?

Answer 1

∆T = imK

∆T = change in freezing point = 11.5º

i = van't Hoff factor = 2 for H2O since it is an electrolyte and produces H+ and OH- ions

m = molality = moles solute/kg solvent = 0.2113 g x 1 mol/18 g / 0.025 kg = 0.4696 mol/kg

K = freezing constant = ?

Solving for K, we have...

K = ∆T / (i)(m) = 11.5º / (2)(0.4696 mol/kg

K = 12.2º/m