CBSE Class 12 Chemistry: Solutions — Important Questions with Answers 2026

Short Answer Questions (2-3 Marks)

• Q: State Raoult's Law. What are ideal and non-ideal solutions?
  Ans: Raoult's Law: The partial vapour pressure of each volatile component in a solution is directly proportional to its mole fraction. p₁ = p₁°x₁ and p₂ = p₂°x₂. Total pressure P = p₁°x₁ + p₂°x₂. Ideal solutions: Obey Raoult's law at all compositions. ΔH_mix = 0, ΔV_mix = 0. Example: benzene + toluene. Non-ideal solutions: Show positive deviation (p > expected, weaker interactions, e.g., ethanol + acetone) or negative deviation (p < expected, stronger interactions, e.g., HCl + water).
• Q: Define colligative properties. Explain elevation in boiling point.
  Ans: Colligative properties depend on the number of solute particles, not their nature. Four types: (1) Relative lowering of vapour pressure. (2) Elevation of boiling point (ΔTb). (3) Depression of freezing point (ΔTf). (4) Osmotic pressure (π). Elevation in boiling point: ΔTb = Kb × m (Kb = molal elevation constant, m = molality). A non-volatile solute lowers vapour pressure, so higher temperature is needed to reach atmospheric pressure for boiling.
• Q: What is osmotic pressure? State Van't Hoff equation.
  Ans: Osmotic pressure (π) is the minimum pressure applied on the solution side to prevent osmosis (flow of solvent from dilute to concentrated through semipermeable membrane). Van't Hoff equation: π = CRT = (n/V)RT, where C = molar concentration, R = gas constant, T = temperature in Kelvin. For electrolytes: π = iCRT (i = Van't Hoff factor). Used for molecular mass determination of polymers, proteins.

Long Answer / Application Questions (4-6 Marks)

• Q: Calculate the boiling point of a solution containing 18 g of glucose (C₆H₁₂O₆) in 100 g of water. Kb = 0.52 K/m.
  Ans: Molar mass of glucose = 180 g/mol. Moles = 18/180 = 0.1 mol. Mass of solvent = 100 g = 0.1 kg. Molality m = 0.1/0.1 = 1 m. ΔTb = Kb × m = 0.52 × 1 = 0.52 K. Boiling point = 100 + 0.52 = 100.52°C.

Exam Tips for This Chapter

• Revise all definitions and laws from Solutions — commonly asked as 1-2 mark questions
• Practice diagrams related to Solutions — neat labelled diagrams carry 2-3 marks
• For numericals, always show formula → substitution → answer with correct units
• Previous year analysis shows Solutions carries significant marks in the board exam