Question

) Which of the following substances would cause the greatest drop in the freezing temperature if we dissolve 1 mol in a fixed amount of water?

A) C6H12O6 (fructose) B) KNO3 C) NaCl D) CaCl2 E) All of these solutions would freeze at the same temperature.

Answer 1

Answer

D) CaCl2

Explanation

Freezing point depression(∆T_f) is calculated by the following equation

∆T_f = K_f × b × i

where,

K_f = freezing point depression constant (which depents on solvent)

b = molality of solute

i = Van't Hoff factor of solute

given subtances are in equal molality and all are in same solvent , so ∆T_f is proportional to van't Hoff factor.

i for C6H12O6 is 1( non electrolyte)

i for KNO3 is 2 ( two ions are formed by dissolution )

i for NaCl is 2 ( two ions are formed by dissolution)

i for CaCl2 is 3 ( three ions are formed by disdolution)

Therefore,

CaCl2 cause greatest drop in freezing point.