Lecture Notes on Solutions

Definition of Solution

• A solution is a homogeneous mixture.
• We will only discuss homogeneous mixtures and avoid heterogeneous mixtures.
• Key Components of Solutions:
  • Solvent: The substance in greater quantity.
  • Solute: The substance in lesser quantity dissolved in the solvent.

Components of Solutions

• There are two main components in a solution:
  • Solvent (always one)
  • Solute (can be one or more)

Examples of Solvent and Solute

• Tea Example:
  • Milk = Solvent
  • Sugar = Solute (can also add salt or other solutes)

Types of Solutions

• Binary Solution: One solvent and one solute
• Ternary Solution: One solvent and two solutes
• Quaternary Solution: One solvent and three solutes

Role of Components

• Solute: Reactive part, dictates the properties (e.g., taste).
• Solvent: Provides the medium for the reaction.

Concentration of Solutions

• The amount of solute in a solution is expressed as concentration.
• Molarity (M): Number of moles of solute per liter of solution.
  • Formula: M = moles of solute / volume of solution in liters
• Molality (m): Moles of solute per kilogram of solvent.
  • Formula: m = moles of solute / mass of solvent in kg

Percentage Concentrations

• Mass by Volume Percentage:
  • Formula: (mass of solute in grams / volume of solution in mL) × 100
• Mass by Mass Percentage:
  • Formula: (mass of solute in grams / mass of solution in grams) × 100
• Volume by Volume Percentage:
  • Formula: (volume of solute in mL / volume of solution in mL) × 100

Mole Fraction

• Mole Fraction (X): Moles of component / total moles in the solution.

Parts per Million (ppm)

• Formula: concentration of solute (g) / mass of solution (g) × 10^6

Vapor Pressure

• Vapor Pressure: The pressure exerted by a vapor in equilibrium with its liquid phase in a closed container.
• Depends on temperature and the nature of the liquid.
• Raoult’s Law: The total pressure of a solution is equal to the sum of the partial pressures of its components.
  • PT = PA + PB

Factors Affecting Vapor Pressure

• Volatile Solutes: Contribute their vapor pressure.
• Non-volatile Solutes: Do not contribute vapor pressure.

Colligative Properties

• Properties that depend only on the number of solute particles and not their nature.
• Examples include boiling point elevation, freezing point depression, and osmotic pressure.

Boiling Point Elevation

• When a non-volatile solute is added to a solvent, the boiling point of the solvent increases.
• Formula: ΔTB = Kb × m
  • Kb = ebullioscopic constant
  • m = molality of the solution

Freezing Point Depression

• The freezing point of a solution is lower than that of the pure solvent.
• Formula: ΔTF = Kf × m
  • Kf = cryoscopic constant
  • m = molality of the solution

Osmotic Pressure

• Pressure required to stop osmosis.
• Formula: π = CRT
  • C = concentration,
  • R = ideal gas constant,
  • T = temperature (in K)

Reverse Osmosis

• A process where pressure is applied to reverse the flow of solvent through a semi-permeable membrane.

Key Terms to Remember

• Isotonic Solutions: Solutions with equal osmotic pressure.
• Colligative properties depend on the number of solute particles.