Question

Which of the following substances show the highest colligative properties?

• A. 0.1M BaCl$_2$
• B. 0.1M AgNO$_3$
• C. 0.1M urea
• D. 0.1M (NH$_4$)$_3$PO$_4$

Hint:

Colligative properties increase with the number of particles in solution. More dissociation leads to stronger effects.

Answer 1

The Correct Option is D

Step 1: Understanding Colligative Properties 
- Colligative properties depend on the number of particles in the solution rather than their nature. 
- The van't Hoff factor (\(i\)) represents the number of ions each molecule dissociates into. 
Step 2: Calculating the Number of Ions 
BaCl$_2$ dissociates into 3 ions: Ba$^{2+}$ and 2Cl$^-$. 
AgNO$_3$ dissociates into 2 ions: Ag$^+$ and NO$_3^-$. 
Urea does not dissociate, so \( i = 1 \).
(NH$_4$)$_3$PO$_4$ dissociates into 4 ions: 3 NH$_4^+$ and 1 PO$_4^{3-}$. 
Step 3: Identifying the Substance with the Highest Colligative Property 
The greater the number of ions, the higher the colligative properties. 
Since (NH$_4$)$_3$PO$_4$ produces 4 ions, it exhibits the highest colligative effect.
Thus, the correct answer is (D).

Answer 2

Step 1: Understand colligative properties
Colligative properties depend on the number of solute particles in solution, not their identity.
These properties include boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure.

Step 2: Importance of van’t Hoff factor (i)
The extent of colligative properties depends on the total number of dissolved particles, which is given by:
Effective concentration = molarity × van’t Hoff factor (i)

Step 3: Analyze the given substance (NH₄)₃PO₄
Ammonium phosphate ((NH₄)₃PO₄) dissociates as:
(NH₄)₃PO₄ → 3 NH₄⁺ + 1 PO₄³⁻
Total particles = 3 + 1 = 4
So, i = 4

Step 4: Comparing with other substances
Other substances with lower dissociation will have smaller i values.
For example, NaCl dissociates into 2 ions (i = 2), CaCl₂ into 3 ions (i = 3).

Step 5: Conclusion
Since 0.1 M (NH₄)₃PO₄ produces the highest number of particles (i = 4), it shows the highest colligative properties.