Question

If you know that a sample of KI in water has a freezing point of -3.2°C, what is the mass% of KI? What is the mole fraction of KI?

Answer 1

Calculate molality of KI solution using the freezing point of the solution. lite - I, (water) –T, (solution) molality = k, (water) _ 0.0 °C-(-3.2 °C), 1=1.72 m 1.86 °C/m Calculate the moles of KI in 100 g of water. 1.72 m = 1.72 mol KI 1 kg of water 1.72 mol KI Moles of KI in 100 g water = 100 g water ® – 1 kg of water x 1000 g 1 kg = 0.172 mol Mass of KI in 100 g water = moles x molar mass = 0.172 mol x 166 g/mol = 28.6 g mass of KI Mass % of KI = _x100= 28.6 8 x100 = 29% mass of water (100 g) 100 g moles of KI 0.172 mol Mole fraction of KI = - moles of KI + moles of water 0.172 mol + 5.55 mol =- on=0.030