Class 12 Chemistry - Solutions

A Solution is a homogeneous mixture of two or more chemically non-reacting substances.

1. Concentration Terms

• Molarity (M): Moles of solute per liter of solution.
• Molality (m): Moles of solute per kg of solvent.
• Mole Fraction (x): Ratio of moles of a component to total moles.
• PPM: Parts per million.

2. Henry's Law

The solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid surface. $P = K_H \cdot x$

3. Raoult's Law

For a solution of volatile liquids, the partial vapor pressure of each component is directly proportional to its mole fraction in the solution. $P_A = P_A^0 \cdot x_A$

• Ideal Solutions: Obey Raoult's law (e.g., Benzene + Toluene).
• Non-Ideal Solutions: Do not obey Raoult's law (Show positive or negative deviations).

4. Colligative Properties

Properties that depend only on the number of solute particles, not their nature.

1. Relative Lowering of Vapor Pressure: $\frac{P^0 - P}{P^0} = x_{solute}$
2. Elevation of Boiling Point: $\Delta T_b = k_b \cdot m$
3. Depression of Freezing Point: $\Delta T_f = k_f \cdot m$
4. Osmotic Pressure: $\pi = CRT$

5. Van't Hoff Factor (i)

To account for dissociation or association of solute particles.

• i > 1 → Dissociation (e.g., NaCl).
• i < 1 → Association (e.g., Acetic acid in benzene).

🧪 Must-Know Numericals

Be prepared to solve problems on:

• Calculation of Moarity and Molality.
• Finding the Molecular Mass using colligative properties.
• Applying the Van't Hoff factor.

Keep practicing the formulas! ⚗️