Overview
This lecture covers the Solutions chapter, explaining types of solutions, concentration expressions, colligative properties, and key laws like Henry’s and Raoult’s laws, with solved example questions.
Types of Solutions
- A solution is a homogeneous mixture with uniform composition and properties throughout.
- A binary solution contains two components: solute (lesser quantity) and solvent (greater quantity).
- Types include gaseous (gas in gas, liquid in gas, solid in gas), liquid (gas in liquid, liquid in liquid, solid in liquid), and solid solutions (solid in solid).
Concentration Terms
- Mass percentage (w/w): mass of component ÷ total mass of solution × 100.
- Volume percentage (v/v): volume of component ÷ total volume of solution × 100.
- Mass by volume percentage (w/v): mass of solute ÷ volume of solution × 100.
- Parts per million (ppm): (parts of component ÷ total parts of solution) × 10⁶.
- Mole fraction (X): moles of component ÷ total moles of all components.
- Molarity (M): moles of solute ÷ liters of solution (temp. dependent).
- Molality (m): moles of solute ÷ kg of solvent (temp. independent).
Solubility & Factors Affecting It
- Solubility is the max amount of solute dissolved at a specific temp.
- For solids in liquids: solubility depends on solute/solvent nature, temp, and is mostly unaffected by pressure.
- For gases in liquids: solubility increases with pressure (Henry's Law) and decreases with temp.
Henry’s Law and Its Applications
- Solubility of a gas is directly proportional to its partial pressure above the liquid.
- Applications: carbonation in beverages, deep-sea diving gas mixes, and effects at high altitudes.
Raoult’s Law & Vapor Pressure
- In an ideal solution of volatile liquids, vapor pressure of each component is proportional to its mole fraction.
- Total vapor pressure = sum of partial pressures of each component.
Ideal and Non-Ideal Solutions
- Ideal solution: obeys Raoult’s law, no enthalpy or volume change on mixing.
- Non-ideal solution: shows positive/negative deviation due to weaker/stronger intermolecular forces.
- Azeotropes: specific mixtures with same liquid and vapor composition, cannot be separated by distillation.
Colligative Properties
- Properties depending on number, not nature, of solute particles: relative lowering of vapor pressure, elevation of boiling point, depression of freezing point, and osmotic pressure.
- Formulas incorporate the van’t Hoff factor (i) to account for association/dissociation.
Example Questions & Calculations
- Detailed sample calculations for molality, molarity, elevation of boiling point, depression of freezing point, and osmotic pressure using provided data.
Key Terms & Definitions
- Solute — component in lesser quantity in a solution.
- Solvent — component in greater quantity, determines solution’s physical state.
- Mole Fraction (X) — ratio of moles of a component to total moles.
- Molarity (M) — moles of solute per liter of solution.
- Molality (m) — moles of solute per kg of solvent.
- Henry’s Law — solubility of gas ∝ partial pressure above solution.
- Raoult’s Law — vapor pressure of component ∝ its mole fraction in solution.
- Colligative Properties — properties depending on number of solute particles.
- Osmosis — solvent movement through semi-permeable membrane from pure solvent to solution.
- Van’t Hoff factor (i) — accounts for association/dissociation in colligative property calculations.
Action Items / Next Steps
- Review solved examples, especially on calculating colligative properties.
- Complete any listed homework or practice problems from the lecture.
- Study key formulas and definitions for upcoming assessments.