Question:

Which of the following solution has the highest freezing point?

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Highest freezing point corresponds to the smallest value of: \[ i\times m \] because freezing point depression is directly proportional to it.
Updated On: Jun 25, 2026
  • \(0.1\ mol\ KCl\) in \(1\ kg\) water
  • \(0.1\ mol\ K_2SO_4\) in \(1\ kg\) water
  • \(0.1\ mol\) Urea in \(1\ kg\) water
  • \(30\ g\) of glucose in \(1\ kg\) water
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The Correct Option is C

Solution and Explanation

Step 1: Use freezing point depression relation.
Freezing point depression is given by: \[ \Delta T_f=iK_fm \] where: \[ i=\text{van't Hoff factor} \] \[ m=\text{molality} \] Higher the value of: \[ i\times m \] greater is the depression in freezing point.
Hence, the solution with the smallest: \[ i\times m \] will have the highest freezing point.

Step 2: Calculate \(i\times m\) for each solution.
For \(KCl\): \[ KCl\rightarrow K^+ + Cl^- \] \[ i=2 \] Thus, \[ i\times m=2\times0.1=0.2 \] For \(K_2SO_4\): \[ K_2SO_4\rightarrow 2K^+ + SO_4^{2-} \] \[ i=3 \] Thus, \[ i\times m=3\times0.1=0.3 \] For urea:
Urea is a non-electrolyte: \[ i=1 \] Thus, \[ i\times m=1\times0.1=0.1 \] For glucose:
Molar mass of glucose: \[ 180\ g\ mol^{-1} \] Moles of glucose: \[ \frac{30}{180}=0.167\ mol \] Thus, \[ m=0.167 \] Since glucose is non-electrolyte: \[ i=1 \] Therefore, \[ i\times m=0.167 \]

Step 3: Compare the values.
\[ K_2SO_4 : 0.3 \] \[ KCl : 0.2 \] \[ \text{Glucose} : 0.167 \] \[ \text{Urea} : 0.1 \] Smallest value is for urea.
Hence, urea solution has minimum freezing point depression and therefore highest freezing point.

Step 4: Final conclusion.
Therefore, the solution with highest freezing point is \[ \boxed{0.1\ mol\ \text{Urea in}\ 1\ kg\ \text{water}} \]
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