Which of the following solutions will have the lowest freezing point in water?
Show Hint
- 0.1 M Glucose
- 0.1 M \(CaCl_2\)
- 0.1 M KCl
- 0.1 M Urea
The Correct Option is B
Solution and Explanation
Freezing point lowering (depression in freezing point) depends on the total number of dissolved particles. The more particles a solute gives in water, the lower the freezing point. The number of particles produced per formula unit is the van't Hoff factor i.
Step 1:
Find i for each solute. Glucose and Urea do not break up, so i = 1. KCl gives \(K^+\) and \(Cl^-\), so i = 2. \(CaCl_2\) gives one \(Ca^{2+}\) and two \(Cl^-\), so i = 3.
Step 2:
Since all are 0.1 M, the depression in freezing point is largest for the solute with the highest i. \(CaCl_2\) has the highest i = 3, so it produces the most particles and the greatest lowering of freezing point.
Answer: Option (B) — 0.1 M \(CaCl_2\) has the lowest freezing point because it gives the maximum number of ions in solution.
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