Solutions

part 1

Types of Solutions and Concentration

• Types of solutions
• Expression of concentration — molarity, molality, mole fraction
• Solubility of gases in liquids — Henry's law
• Solubility of solids in liquids

part 2

Vapour Pressure and Raoult's Law

• Vapour pressure of liquid solutions
• Raoult's law for volatile solutes
• Ideal and non-ideal solutions
• Azeotropes

part 3

Colligative Properties

• Relative lowering of vapour pressure
• Elevation of boiling point
• Depression of freezing point
• Osmosis and osmotic pressure
• Abnormal molar masses — van't Hoff factor

Raoult's law (ideal solution)

$p_A = x_A \cdot p^\circ_A$ (Raoult's law)

★ board favourite

Total pressure of ideal binary solution

$P_{total} = x_A p^\circ_A + x_B p^\circ_B$

★ board favourite

Elevation in boiling point

$\Delta T_b = K_b \cdot m$ (Kb = molal elevation constant)

★ board favourite

Depression in freezing point

$\Delta T_f = K_f \cdot m$ (Kf = molal depression constant)

★ board favourite

Osmotic pressure

$\pi = CRT = \frac{n}{V}RT$

★ board favourite

Henry's law (gas in liquid)

$p = K_H \cdot x$ (K_H = Henry's constant)

★ frequently asked

van't Hoff factor

$i$ = observed colligative property / calculated value (no assoc./dissoc.)

★ frequently asked

Molality

$m = \frac{\text{moles of solute}}{\text{kg of solvent}}$

★ frequently asked

Mole fraction

$x_A = \frac{n_A}{n_A + n_B}$

★ frequently asked

Define osmotic pressure. 200 cm³ of an aqueous solution of a protein contains 1.26 g of the protein. The osmotic pressure of such a solution at 300 K is found to be 2.57×10⁻³ bar. Calculate the molar mass of the protein. (R = 0.083 L·bar·K⁻¹·mol⁻¹)

Define the van't Hoff factor. What is its value for (i) a strong electrolyte like NaCl and (ii) a solute that undergoes dimerisation in solution?

What is the elevation of boiling point? Derive an expression for it and define ebullioscopic constant. 2g of a non-volatile solute dissolved in 100g of water elevates boiling point by 0.104°C. Find the molar mass. (Kb = 0.52 K·kg/mol)

(a) Define depression in freezing point and cryoscopic constant. (b) 45 g of ethylene glycol (C₂H₆O₂) is mixed with 600 g of water. Calculate (i) the freezing point depression and (ii) the freezing point of the solution. (Kf of water = 1.86 K·kg/mol)

State Raoult's law for a solution of volatile liquids. Why do solutions showing negative deviation from Raoult's law have lower vapour pressure than ideal solutions?

State Henry's law. Explain why (i) aquatic species are more comfortable in cold water than in warm water, and (ii) a soft drink bottle is sealed under high pressure of CO₂.

Define molality and mole fraction. Why is molality preferred over molarity for expressing the concentration of a solution in colligative-property calculations?

What is meant by abnormal molar mass? Explain, with the help of the van't Hoff factor, how association and dissociation of a solute lead to abnormal molar masses.

Give an example of a solution that shows positive deviation from Raoult's law.

(a) Derive the relationship between molar mass of a solute and the elevation in boiling point. (b) 18 g of glucose (C₆H₁₂O₆) is dissolved in 1 kg of water. At what temperature will the solution boil at 1.013 bar? (Kb for water = 0.52 K·kg/mol, boiling point of water = 373.15 K)

How many marks is Solutions worth in the Class 12 board exam?

Around 7 marks of the 70-mark CBSE Chemistry theory paper, based on the official unit-wise weightage. Raoult's law and colligative properties numerics — high yield.

Is Solutions easy or hard?

It's rated medium — a moderate-difficulty chapter in Class 12 Chemistry. Most students need about 5 hours to cover it well.

What are the important topics in Solutions?

The chapter covers 11 NCERT topics in 3 areas: Types of Solutions and Concentration; Vapour Pressure and Raoult's Law; Colligative Properties.

What questions come from Solutions in board exams?

Between 2018–2024, CBSE board papers asked questions from this chapter on Osmotic Pressure, Van't Hoff Factor, Colligative Properties, Raoult's Law — 1- to 5-mark questions.