ISC 12 Chemistry Revision notes 2024-25

Chapter 1: Solutions

Solution and Its Types

A solution is a homogeneous mixture of two or more pure substances.

Two constituents of the solution:

  • Solute: The substance present in small quantity (e.g., sugar, salt).

  • Solvent: The substance present in larger quantity (e.g., water).

Types of solutions based on states of matter can be classified into nine different types:

  • Solid-Solid: Alloys

  • Solid-Liquid: Sugar dissolved in water.

  • Solid-Gas: Sublimed substances like iodine.

  • Liquid-Solid: Hydrated salts.

  • Liquid-Liquid: Alcohol in water.

  • Liquid-Gas: Aerosols.

  • Gas-Solid: Hydrogen absorbed in palladium.

  • Gas-Liquid: Carbonated drinks.

  • Gas-Gas: Mixture of gases.

Causes of Solubility

Factors contributing to solubility:

  • Inter-ionic attraction: Stabilizes the solute in the lattice.

  • Inter-molecular attraction: Between solvent and solute.

  • Solvation: Attraction between solvent and solute molecules.

  • Temperature: Affects the solubility based on the nature of the solute.

Deciding Factors for Solubility

  • Nature of solute and solvent: "Like dissolves like"; polar solvents dissolve polar solutes, etc.

  • Temperature: Generally increases solubility, but exceptions exist for some exothermic reactions.

  • Pressure: Major effect on gas solubility.

  • Hydration energy: Energy released when ions are hydrated.

Concentration of Solutions

Concentration can be expressed as:

  • Mass percentage:

    • Mass% = (Mass of solute / Total mass of solution) × 100

  • Volume percentage:

    • Volume% = (Volume of solute / Total volume of solution) × 100

  • Mass by volume percentage:

    • Mass by Volume% = (Mass of solute / Volume of solution) × 100

  • Mole fraction: Ratio of moles of a component to total moles.

  • Molarity (M):

    • M = (Number of moles of solute / Volume of solution in L)

  • Molality (m):

    • m = (Number of moles of solute / Mass of solvent in kg)

  • Normality (N):

    • N = (Number of equivalents of solute / Volume of solution in L)

  • Parts per million (ppm):

    • ppm = (Mass of solute / Mass of solution) × 10^6

Relationship between Concentration Measures

  • Molarity relates to molality depending on density.

  • Solutions can also be expressed with Henry’s law for gas solubility.

Henry's Law

Relates gas pressure to its solubility in liquids:

  • p = K_H * c (where p is the partial pressure of the gas, K_H is Henry's constant, and c is the gas concentration).

Key Terms and Concepts

  • ISO: Molar, mass percent, volume percent.

  • Colligative properties: These depend on the concentration of solute particles.

  • Ideal solutions: Solutions that follow Raoult’s law, which states that vapor pressure of each component is proportional to its mole fraction.

  • Real solutions: Show deviations from Raoult’s law due to intermolecular forces.