Solutions and Colligative Properties – NEET Chemistry Class 12

Solutions and colligative properties are fundamental concepts in physical chemistry. They explain how solutes affect physical properties of solvents like vapor pressure, freezing point, boiling point, and osmotic pressure. This chapter is frequently tested in NEET because it combines conceptual understanding, numerical problems, and application-based questions.

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Introduction to Solutions

• A solution is a homogeneous mixture of solute(s) dissolved in a solvent.

• Solutions can be solid, liquid, or gaseous, but NEET mostly focuses on liquid solutions.

• Understanding solution properties is essential for explaining colligative effects.

Types of Solutions

1. Dilute Solution – Solute concentration is low.

2. Concentrated Solution – Solute concentration is high.

3. Saturated Solution – Maximum solute dissolves at a given temperature.

4. Unsaturated Solution – Less than maximum solute is dissolved.

5. Supersaturated Solution – More solute dissolved than the saturation limit (unstable).

Colligative Properties

Colligative properties depend only on the number of solute particles, not their chemical identity. Key colligative properties include:

1. Relative Lowering of Vapor Pressure

   • Raoult’s Law: P_solvent = X_solvent × P°_solvent

   • Dependent on mole fraction of solute.

2. Elevation of Boiling Point

   • ΔT_b = K_b × m × i

   • Boiling point increases when a non-volatile solute is added.

3. Depression of Freezing Point

   • ΔT_f = K_f × m × i

   • Freezing point decreases in presence of a solute.

4. Osmotic Pressure

   • π = nRT/V

   • Determines movement of solvent across a semipermeable membrane.

Here, m = molality, i = van’t Hoff factor, K_b/K_f = ebullioscopic/cryoscopic constants

Applications of Colligative Properties

• Determining molar masses of solutes

• Antifreeze in cars (freezing point depression)

• Salt on icy roads (freezing point depression)

• Reverse osmosis for water purification

• Blood plasma osmotic pressure in medical studies

Importance for NEET Preparation

• Questions often involve numerical calculations based on colligative properties.

• Conceptual understanding of Raoult’s Law and van’t Hoff factor is essential.

• Application-based questions are frequently asked in NEET to test reasoning and problem-solving.

Previous Year NEET Questions – Insights

• Calculating ΔT_b, ΔT_f, and osmotic pressure for solutions

• Determining molar mass of solutes from colligative properties

• Questions involving Raoult’s Law and ideal/non-ideal solutions

• Application-based scenarios like blood plasma, antifreeze, and food preservation

Study Tips for Students

1. Memorize Key Formulas – ΔT_b, ΔT_f, π = nRT/V, Raoult’s Law

2. Practice Numerical Problems – Focus on unit conversions and van’t Hoff factor

3. Understand Concept of Molality vs Molarity – Crucial for colligative properties

4. Refer NCERT Examples – Most NEET questions are directly based on NCERT

5. Solve Previous Year Questions – Improves speed and conceptual clarity

Conclusion

Mastering Solutions and Colligative Properties is essential for NEET success. This chapter helps students solve numerical problems, understand physical chemistry principles, and apply concepts in real-life scenarios. A strong foundation in this topic ensures confidence in both theory-based and problem-solving questions.