why is freezing point depression of 0.1 M NaCl solution nearly twice that of 0.1 M glucose solution?
0.1M NaCl and 0.1M glucose solution means that, 0.1 mole of NaCl and 0.1 mole of glucose is present in 1L of solvent. The weight of solvent in both the solution is same. We know that, the depression in the freezing point can be calculated as:
where, Kf = Molal depression constant
wB = weight of the solute
wA = weight of the solvent
MB = Molar mass of the solute.
MNaCl = 58.6 g/mol
MC6H12O6 = 180 g/mol
The depression in freezing point is inversely proportional to Molar mass of the solute, the more is the Molar mass of the solute lesser will be the depression in the freezing point. Thus, it can be explained that the depression in freezing point of NaCl will be more than the depression in the freezing point of glucose.