Overview
This lecture covers the Solutions chapter for Class 12 Chemistry, including types of solutions, concentration terms, Raoult's Law, colligative properties, and related calculations relevant for CBSE 2024 exams.
Types of Solutions
- Solutions are homogeneous mixtures of two or more substances.
- The substance present in larger amount is called the solvent; the one in lesser amount is the solute.
- Types of solutions: solid in solid, solid in liquid, gas in liquid, gas in gas, etc.
Concentration Terms
- Molarity (M): moles of solute per liter of solution.
- Molality (m): moles of solute per kilogram of solvent.
- Mole fraction (X): ratio of moles of a component to total moles in solution.
- Mass percent: mass of solute per 100 g of solution.
Solubility and Factors Affecting It
- Solubility: maximum amount of solute that can dissolve in solvent at given conditions.
- Factors: temperature (usually increases solubility of solids in liquids), pressure (affects gases in liquids).
Raoult's Law and Deviations
- Raoult's Law: partial vapor pressure of each component in solution is proportional to its mole fraction.
- Ideal solutions obey Raoult's Law; non-ideal solutions show positive or negative deviations due to solute-solvent interactions.
Colligative Properties
- Colligative properties depend on the number of solute particles, not their identity.
- Types: relative lowering of vapor pressure, elevation of boiling point, depression of freezing point, and osmotic pressure.
- Formulas:
- ฮTf = Kf ร molality (freezing point depression)
- ฮTb = Kb ร molality (boiling point elevation)
- ฯ = C ร R ร T (osmotic pressure)
Abnormal Molar Masses
- Abnormal molar masses arise due to association or dissociation of solute in solution.
- van't Hoff factor (i) corrects for this in colligative property formulas.
Osmosis and Osmotic Pressure
- Osmosis: passage of solvent through a semipermeable membrane from dilute to concentrated solution.
- Osmotic pressure is the pressure required to stop osmosis; calculated by ฯ = nRT/V.
Key Terms & Definitions
- Solution โ homogeneous mixture of two or more substances.
- Solute โ component present in lesser amount in solution.
- Solvent โ component present in greater amount in solution.
- Molarity (M) โ moles of solute per liter solution.
- Molality (m) โ moles of solute per kg solvent.
- Mole Fraction (X) โ fraction of moles of a component to total moles.
- Colligative Properties โ properties depending on the number of solute particles.
- Raoult's Law โ states partial vapor pressure is proportional to mole fraction.
- Osmosis โ movement of solvent across a semipermeable membrane.
- van't Hoff Factor (i) โ correction factor for abnormal molar masses.
Action Items / Next Steps
- Practice numerical problems on colligative properties and concentration calculations.
- Review differences between ideal and non-ideal solutions.
- Revise all formulas and definitions from this chapter.