Question

Which of the following solutions has highest osmotic pressure?

• A. \(1\,M\;NaCl\)
• B. \(1\,M\;MgCl_2\)
• C. \(1\,M\;\text{urea}\)
• D. \(1\,M\;\text{glucose}\)

Hint:

For colligative properties, ionic compounds show greater effect than non-electrolytes because they dissociate into multiple ions. Always compare the van't Hoff factor \(i\): \[ \text{Higher } i \Rightarrow \text{Higher osmotic pressure} \]

Answer 1

The Correct Option is B

Concept: Osmotic pressure is a colligative property and depends upon the total number of solute particles present in the solution. It is given by the relation: \[ \pi = iCRT \] where:
• \( \pi \) = osmotic pressure
• \( i \) = van't Hoff factor
• \( C \) = molar concentration
• \( R \) = gas constant
• \( T \) = absolute temperature For solutions of equal concentration at the same temperature: \[ \pi \propto i \] Hence, the solution producing maximum number of particles will have the highest osmotic pressure.

Step 1: Determining van't Hoff factor for each solution.

• \(NaCl \rightarrow Na^+ + Cl^-\) Total particles formed \(=2\) Therefore, \[ i \approx 2 \]
• \(MgCl_2 \rightarrow Mg^{2+} + 2Cl^-\) Total particles formed \(=3\) Therefore, \[ i \approx 3 \]
• Urea is a non-electrolyte and does not dissociate. Therefore, \[ i=1 \]
• Glucose is also a non-electrolyte. Therefore, \[ i=1 \]

Step 2: Comparing osmotic pressures.
Since all solutions are \(1\,M\) and temperature is same: \[ \pi \propto i \] Comparing values: \[ MgCl_2 > NaCl > \text{urea} = \text{glucose} \] Thus, \(1\,M\;MgCl_2\) has the highest osmotic pressure.