CBSE Class 12 Chemistry: Solutions — Concentration & Colligative Notes 2026

Types of Solutions

• Gas-gas, gas-liquid, gas-solid, liquid-liquid, liquid-solid, solid-solid solutions
• Ideal solutions: obey Raoult's law; Δ_mix H = 0, Δ_mix V = 0
• Non-ideal: positive or negative deviations from Raoult's law (maximum/minimum boiling azeotropes)

Concentration Terms

• Molarity (M) = moles solute / litres solution; temperature-dependent
• Molality (m) = moles solute / kg solvent; temperature-independent
• Mole fraction: x_A = n_A/(n_A+n_B); mass percent = (mass solute / mass solution) × 100

Henry's Law and Raoult's Law

• Henry's law: p = K_H × x; solubility of gas increases with pressure (soda fizz)
• Raoult's law for volatile solute: p_A = x_A × p°_A; total pressure = sum of partial pressures
• Vapour pressure of solution < pure solvent (non-volatile solute): elevation of bp, depression of fp

Colligative Properties

• Properties that depend on number of solute particles, not their nature
• Relative lowering of vapour pressure: (p°−p)/p° = x₂ (mole fraction of solute)
• Elevation of boiling point: ΔTb = Kb × m; depression of freezing point: ΔTf = Kf × m

Osmosis and Osmotic Pressure

• Osmosis: flow of solvent through semipermeable membrane from dilute to concentrated solution
• Van't Hoff equation: π = CRT = nRT/V (for dilute solutions)
• Applications: reverse osmosis (water purification), preservation (jams, pickles)

Abnormal Molar Masses

• Dissociation increases particle count; association decreases it
• Van't Hoff factor i: i > 1 for dissociation; i < 1 for association
• Modified colligative properties: ΔTb = i × Kb × m; ΔTf = i × Kf × m

CBSE Exam — Solutions

• Calculate ΔTf for 1.86 g of glucose in 100 g water; Kf(water) = 1.86 K/m
• Define: isotonic solutions, hypotonic, hypertonic; biological examples
• Henry's law: CO₂ pressure above soda at 25°C; find dissolved CO₂ concentration