W2 LV1 - Dissolution and Solubility Principles

Overview

• Lecture series: CHEM 1011 Week 2 — General Chemistry II topics.
• Main lecture: "The Dissolution Process" with related videos on solubility, Henry's Law, colligative properties, and osmosis.
• Purpose: Explain how substances dissolve, factors affecting solubility, gas solubility laws, and colligative effects.

The Dissolution Process

• Dissolution: process by which solute particles disperse uniformly in solvent to form a solution.
• Steps: separation of solute particles, separation of solvent molecules, interaction between solute and solvent.
• Energy changes: dissolution can be endothermic or exothermic depending on bond-breaking and bond-forming energies.
• Factors affecting dissolution: temperature, pressure (for gases), and nature of solute/solvent (polarity, ionic character).

Solubility

• Solubility: maximum amount of solute that dissolves in a given solvent at equilibrium and specified temperature.
• Saturated solution: contains maximum dissolved solute at that temperature.
• Unsaturated: can dissolve more solute.
• Supersaturated: contains more dissolved solute than equilibrium; metastable.
• Temperature effects: for most solids, solubility increases with temperature; exceptions exist.
• Solvent–solute interaction: "like dissolves like" — polar solvents dissolve polar/ionic solutes; nonpolar solvents dissolve nonpolar solutes.

Henry's Law (Gas Solubility)

• Henry's Law: solubility of a gas in a liquid is proportional to its partial pressure above the liquid.
• Formula: S = kH × P (S = solubility; kH = Henry's constant; P = partial pressure).
• Temperature effect: gas solubility typically decreases as temperature increases.
• Applications: carbonation of beverages, gas exchange in lungs, environmental solubility of gases.

Colligative Properties

• Definition: properties of solutions that depend on the number of solute particles, not their identity.
• Examples: vapor pressure lowering, boiling point elevation, freezing point depression, osmotic pressure.
• Van ’t Hoff factor (i): accounts for dissociation of solutes into particles in solution.
• Formulas:
  • Boiling point elevation: ΔTb = i × Kb × m
  • Freezing point depression: ΔTf = i × Kf × m
  • Osmotic pressure: π = i × M × R × T
  • m = molality; M = molarity; Kb/Kf = solvent constants; R = gas constant; T = temperature (K).

Osmosis

• Osmosis: net flow of solvent through a semipermeable membrane from low to high solute concentration.
• Osmotic pressure: pressure required to stop osmotic flow; depends on solute particle concentration.
• Biological relevance: cell volume regulation, dialysis, and blood plasma osmolarity.
• Practical note: use colligative formulas to calculate osmotic pressure for ideal dilute solutions.

Key Terms and Definitions

• Dissolution: formation of a homogeneous solution by dispersing solute in solvent.
• Solubility: maximum solute amount dissolvable at equilibrium for given conditions.
• Henry's Law: relation between gas solubility and partial pressure.
• Colligative Property: solution property dependent on number of solute particles.
• Van ’t Hoff Factor (i): effective number of particles produced per solute formula unit.
• Molality (m): moles of solute per kilogram of solvent.
• Molarity (M): moles of solute per liter of solution.
• Osmotic Pressure (π): pressure needed to prevent solvent flow across membrane.

Action Items / Next Steps

• Practice problems: compute ΔTb, ΔTf, and π for given solutions using i, Kb, Kf, m, and M.
• Apply Henry's Law: calculate gas solubility changes with varying partial pressures.
• Predict solubility trends: use polarity and temperature to explain experimental observations.
• Review real-world examples: carbonation, antifreeze (freezing point depression), dialysis procedures.