Lecture Notes on Solutions and Colligative Properties

Introduction to Solutions

• Definition: A solution is a homogeneous mixture of two or more components.
  • Homogeneous: Uniform composition throughout.
• Components:
  • Solute: Substance dissolved in the solvent.
  • Solvent: Substance that dissolves the solute.

Types of Solutions

• Gaseous Solutions:
  • Example: Oxygen and nitrogen gas mixture.
  • Solvent and solute are both gases.
• Liquid Solutions:
  • Solvent is in the liquid state.
• Solid Solutions:
  • Solvent is a solid.

Concentration of Solutions

• Concentrated Solution: High amount of solute.
• Dilute Solution: Low amount of solute.

Concentration Terms

• Mole Fraction:
  • Formula: ( \text{Mole fraction} = \frac{\text{Number of moles of a component}}{\text{Total number of moles in the solution}} )
  • Example Calculation: 1.8g glucose in 90g water.

Solubility

• Definition: Maximum amount of solute that can be dissolved in a solvent at a specific temperature.
• Factors affecting solubility include the nature of solute and solvent, and temperature.

Types of Solutions Based on Solubility

• Saturated Solution: Maximum solute dissolved.
• Unsaturated Solution: Less than maximum solute dissolved.
• Supersaturated Solution: More solute than possible dissolved, generally unstable.

Henry's Law

• Law Statement: Solubility of a gas in liquid is directly proportional to the partial pressure of the gas.
• Formula: ( P = K_H \cdot X )
  • ( P ): Partial pressure of the gas.
  • ( K_H ): Henry's law constant.
  • ( X ): Mole fraction of gas.

Vapor Pressure and Raoult's Law

• Vapor Pressure: Pressure exerted by vapor in equilibrium with its liquid at a given temperature.
• Raoult’s Law: The partial vapor pressure of each volatile component in a solution is proportional to its mole fraction.

Ideal and Non-Ideal Solutions

• Ideal Solutions: Obey Raoult's law.
• Non-Ideal Solutions: Show deviations from Raoult's law.
  • Positive Deviations: Interaction between molecules is weaker.
  • Negative Deviations: Interaction between molecules is stronger.

Colligative Properties

• Properties that depend on the number of solute particles, not their nature.
  • Relative Lowering of Vapor Pressure
  • Boiling Point Elevation
  • Freezing Point Depression
  • Osmotic Pressure

Calculations Involving Colligative Properties

• Boiling Point Elevation: ( \Delta T_b = i \cdot K_b \cdot m )
• Freezing Point Depression: ( \Delta T_f = i \cdot K_f \cdot m )
• Osmotic Pressure: ( \Pi = i \cdot CRT )
  • ( i ): Van’t Hoff factor.
  • ( C ): Concentration.
  • ( R ): Universal gas constant.
  • ( T ): Temperature in Kelvin.

Osmosis and Osmotic Pressure

• Osmosis: Movement of solvent through a semi-permeable membrane from a region of lower solute concentration to higher.
• Osmotic Pressure: Pressure required to stop osmosis.

Van’t Hoff Factor

• Adjusts for dissociation and association of solute particles.
  • Association: Decreases number of particles.
  • Dissociation: Increases number of particles.

Applications

• Colligative properties are used to determine molecular masses of solutes and have practical applications in desalination and other fields.

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These notes summarize key concepts from the lecture on solutions and their properties, focusing on the types, concentrations, solubility, and colligative properties.