Question

Choose the aqueous solution below with the lowest freezing point. These are all solutions of nonvolatile solutes and you should assume ideal van't hoff factors where applicable.

1) Solution A: 0.1 M NaCl
2) Solution B: 0.2 M KCl
3) Solution C: 0.3 M CaCl2
4) Solution D: 0.4 M MgCl2

Answer 1

To find the solution with the lowest freezing point, we look at effective concentrations of particles resulting from dissociation. Solution D, which is 0.4 M MgCl2 with a van't Hoff factor of 3, has the highest particle concentration and therefore the lowest freezing point among the options.

Step-by-step explanation:

To determine the aqueous solution with the lowest freezing point, we consider the effect of the solute particles on the freezing point depression. The freezing point depression is directly proportional to the molal concentration of solute particles in the solution. Since we are comparing solutions of nonvolatile solutes, we will consider the van't Hoff factor, which provides the number of particles into which a compound dissociates in solution.

NaCl, KCl, CaCl2, and MgCl2 dissociate into 2, 2, 3, and 3 particles per formula unit respectively. To find the effective concentration of particles we multiply the molarity of each solution by the number of particles it dissociates into:

• 0.1 M NaCl × 2 = 0.2
• 0.2 M KCl × 2 = 0.4
• 0.3 M CaCl2 × 3 = 0.9
• 0.4 M MgCl2 × 3 = 1.2

The solution with the highest concentration of particles will have the lowest freezing point. Thus, Solution D: 0.4 M MgCl2 has the highest effective concentration of particles and, consequently, the lowest freezing point among the given options.