Solutions Lecture Notes

Introduction to Solutions

• Definition: A solution is a homogeneous mixture of two or more chemically non-reacting substances, which can change composition within certain limits.
• Phase: Regarded as a singular phase having more than one component.
• Components:
  • Solute: Present in smaller quantities.
  • Solvent: Present in larger quantities.
• Binary Solution: Contains two components.

Types of Solutions

Solutions of Solids in Liquids

• Saturated Solution: Contains as much solute as can dissolve at a given temperature.
• Unsaturated Solution: Contains less solute than it can dissolve.
• Supersaturated Solution: Contains more solute than it can dissolve at a particular temperature.

Solubility

• Solubility of Solids
  • Exothermic substances (e.g., KOH, CaO) have solubility inversely proportional to temperature.
  • Endothermic substances (e.g., NaCl, KNO₃) have solubility directly proportional to temperature.
• Solubility of Gases
  • Described by absorption coefficient.
  • Depends on temperature, nature of gas, solvent, and pressure (Henry's law).

Henry's Law

• Solubility of a gas in a liquid at constant temperature is directly proportional to the pressure of the gas.
• Applications: Soft drinks, scuba diving.

Expression of Concentration

• Solubility: Amount of solute dissolved in a specific volume of solution.
• Molarity (M): Moles of solute per liter of solution.
• Molality (m): Moles of solute per kilogram of solvent.
• Normality (N): Gram equivalents of solute per liter of solution.
• Formality (F): Gram formula units per liter of solution.

Vapour Pressure

• Definition: Pressure exerted by vapour in equilibrium with the liquid at a specific temperature.
• Raoult's Law: For non-volatile solutes, the relative lowering of vapour pressure is equal to the mole fraction of the solute.
• Ideal vs Non-Ideal Solutions
  • Ideal: No deviation from Raoult's Law.
  • Non-Ideal: Show positive or negative deviations.

Azeotropic Mixtures

• Definition: Mixtures with the same boiling point that cannot be separated by distillation.
• Types:
  • Minimum boiling azeotropes: Positive deviation.
  • Maximum boiling azeotropes: Negative deviation.

Colligative Properties

• Depend only on the number of solute particles, not their nature.
• Properties:
  • Relative lowering of vapour pressure.
  • Osmotic pressure.
  • Elevation in boiling point.
  • Depression in freezing point.

Osmosis

• Net flow of solvent from lower to higher concentration through a semi-permeable membrane.
• Osmotic Pressure: Minimum pressure to prevent solvent flow into the solution.

Vant Hoff Factor

• Describes degree of dissociation or association in a solution.
• i > 1: Dissociation.
• i < 1: Association.

Questions and Answers

• Answered various conceptual questions regarding solutions, solubility, colligative properties, and related phenomena.

Chapter Summary

• Overview of key concepts such as solutions, concentration, vapour pressure, and colligative properties.
• Mentioned methods for preparing and analyzing colloids, and applications of different laws and principles in practical scenarios.