Calculate the freezing point of a 1.0 m solution of Ca(NO₃)₂ in water. Remember that Mg(NO₃)₂ is an electrolyte. The normal freezing point of pure water is 0.00ºC. K_f (water)= -1.86ºC/m. A)1.56 ºC B)5.58ºC C)1.86ºC D)-5.58ºC E)-1.86ºC

Question

Quizplus · Accepted Answer

Using the formula: ΔTf = i Kf molality where ΔTf is the change in freezing point, Kf is the freezing point depression constant, i is the van't Hoff factor, and molality is the concentration in mol/kg. The van't Hoff factor for Ca(NO₃)₂ is 3, because it dissociates into three ions in water: Ca2+ and two NO3- ions. ΔTf = 3 * (-1.86ºC/m) * 1.0 mol/kg = -5.58ºC Therefore, the freezing point of the solution is 0ºC - 5.58ºC = -5.58ºC. Choice D is the correct answer.

Calculate the Freezing Point of a 1