Question

Calcium chloride, CaCl2, has been used to melt ice from roadways. Given that a solution is 25% CaCl2 by mass, estimate the freezing point.

Answer 1

notice you get three ions per formula.

deltatemp=3*(-1.8)molality


now, molality: moles/kg solvent.

assume .75 kg solvent, then mass of solute must be 250grams, to give a twenty-five percent.

molesCaCl2=250/110 about figure it out.

molality=about 2.4/.75 you need to do this accurately.

Answer 2

CaCl2 = have 3 ions

delta temp = 3*(-1.858)molality = -5.57 x molality
molality = moles solute/kg solvent.

assume 0.75 kg solvent, then mass of solute must be 250 grams, to give a 25 %.

moles CaCl2 = 250/110 = 2.27 mol
molality = 2.27 mol / 0.75 kg = 3.03 m

Delta Temp = 3*(-1.858)*3.03 = -16.9 C


Thanks Bobpursley