12. Which of the following aqueous solutions would be expected to have the lowest freezing point? A) 0.400 m K2SO4 B) 0.400 m NaCl C) 0.400 m C6H12O6 (glucose) D) 0.040 m K2SO4 E) 0.040 m NaCl
Freezing point of water is depressed (lowered) by the addition of a solute. The amount of depression in freezing point depends on the molality of solute particles in that solution. Higher the molality, lowest the freezing point.
A. 0.4 m K2SO4 has (0.4*2) = 0.8 m K+ ions and 0.4 m SO4- ions. Total particles = 0.8+0.4 = 1.2 m
B. 0.4 m NaCl has 0.4 m Na+ ions and 0.4 m Cl- ions. Total particles = 0.4 +0.4 = 0.8m
C. 0.4 m C6H12O6 has 0.4 m C6H12O6 ions. Total particles = 0.4 m
D. 0.04 m K2SO4 has (0.04*2) = 0.08 m K+ ions and 0.04 m SO4- ions. Total particles = 0.08+0.04 = 0.12 m
E. 0.04 m NaCl has 0.04 m Na+ ions and 0.04 m Cl- ions. Total particles = 0.04 +0.04 = 0.08m
Therefore A. 0.4 m K2SO4 has highest molality and lowest freezing poing point.