Question

Van’t Hoff factors of aqueous solutions of \(X, Y, Z\) are \(1.8,\;0.8\) and \(2.5\) respectively. Hence, their:

• A. boiling point: \(Z<X<Y\)
• B. freezing point: \(Z<X<Y\)
• C. osmotic pressure: \(X = Y = Z\)
• D. vapour pressure: \(Y<X<Z\)

Hint:

For colligative properties: \[ \Delta T_b,\; \Delta T_f,\; \pi \propto i \] Higher Van’t Hoff factor means stronger colligative effect.

Answer 1

The Correct Option is A

Step 1: Recall the role of Van’t Hoff factor. The Van’t Hoff factor \(i\) accounts for the number of effective particles in solution. All colligative properties depend directly on \(i\).
Step 2: Write the relation for elevation in boiling point. \[ \Delta T_b = iK_b m \] Thus, \[ \Delta T_b \propto i \]
Step 3: Compare the given Van’t Hoff factors. \[ i_X = 1.8,\quad i_Y = 2.5,\quad i_Z = 0.8 \] Greater the value of \(i\), greater is the elevation in boiling point.
Step 4: Arrange the boiling points. \[ \Delta T_b(Z)<\Delta T_b(X)<\Delta T_b(Y) \] Hence, \[ \text{Boiling point: } Z<X<Y \] Therefore, the correct option is \[ \boxed{\text{boiling point: } Z<X<Y} \]