What volume of ethanol (density = 0.7893 g/cm3) should be added to 450. ml of water in order to have a solution that freezes at â15.0°c? (for water, kf = 1.86 °c/m.)?
According to this formula : ΔTf= i Kf m i is van't Hoff factor= 1 Kf = 1.86 m the molality we need to assume it m= x moles of C2H5OH / Kg of mass ∴ 15 = 1 * 1.86 * ( x moles of C2H5OH/ 0.45 kg) ∴X = 3.629 moles mass = no.of moles x molar mass of C2H5OH = 3.629 X 46 = 167 g ∴the volume = mass / denisty = 167 / 0.7893 = 211.57≈ 212 mL
