Question

Arrange the following solutions in order by their decreasing freezing points: 0.1 m Na₃PO₄, 0.1 m C₂H₅OH, 0.01 m CO₂, 0.15 m NaCl, and 0.2 m CaCₗ₂.

a) 0.2 m CaCl₂ > 0.15 m NaCl > 0.1 m C₂H₅OH > 0.1 m Na₃PO₄ > 0.01 m CO₂
b) 0.2 m CaCl₂ > 0.15 m NaCl > 0.1 m Na₃PO₄ > 0.1 m C₂H₅OH > 0.01 m CO₂
c) 0.2 m CaCl₂ > 0.15 m NaCl > 0.1 m C₂H₅OH > 0.01 m CO₂ > 0.1 m Na₃PO₄
d) 0.2 m CaCl₂ > 0.15 m NaCl > 0.01 m CO₂ > 0.1 m C₂H₅OH > 0.1 m Na₃PO₄

Answer 1

To determine the order of decreasing freezing points, consider both the molarity of solutions and the number of particles they dissociate into (van 't Hoff factor). 0.2 m CaCl2 will have the lowest freezing point, followed by 0.15 m NaCl, 0.1 m Na3PO4, 0.1 m C2H5OH, and finally 0.01 m CO2 with the highest freezing point.

Step-by-step explanation:

To order solutions by their decreasing freezing points, you need to understand how solutes affect freezing point depression. The more particles a solution has, the lower its freezing point will be. This concept is tied to the van 't Hoff factor (i), which is the number of particles the solute dissociates into in solution.

Given the following solutions and their concentrations, we can apply the concept:

• 0.1 m Na₃PO₄ (Na₃PO₄ dissociates into 4 particles: 3 Na+ and 1 PO₄³−)
• 0.1 m C₂H₅OH (ethanol does not dissociate, i = 1)
• 0.01 m CO₂ (carbon dioxide is a non-electrolyte and does not dissociate in water, i = 1)
• 0.15 m NaCl (NaCl dissociates into 2 particles: Na+ and Cl−)
• 0.2 m CaCl₂ (CaCl₂ dissociates into 3 particles: Ca²+ and 2 Cl−)

Accounting for both molarity and the van 't Hoff factor, the solutions ordered from lowest to highest freezing points (or decreasing freezing points) is:

Answer: 0.2 m CaCl₂ (most particles, i=3) > 0.15 m NaCl (next highest, i=2) > 0.1 m Na₃PO₄ (i=4, but at a lower molarity) > 0.1 m C₂H₅OH (non-electrolyte, i=1) > 0.01 m CO₂ (lowest concentration of particles, i=1).