Chemistry: Solutions

Key Objectives

• Understand the formation of different types of solutions.
• Express concentration in various units.
• Understand Henry's law and Raoult's law.
• Distinguish between ideal and non-ideal solutions.
• Explain deviations from Raoult's law in real solutions.
• Describe colligative properties and correlate with solute molar masses.
• Explain abnormal colligative properties in certain solutes.

Introduction

• Most substances we encounter are mixtures.
• The importance of mixtures depends on their composition.
• Examples: Brass, fluoride in water, intravenous solutions.
• Focus on liquid solutions and their properties.

Types of Solutions

• Gaseous Solutions: Mixture of gases like oxygen and nitrogen.
• Liquid Solutions: Solute can be gas, liquid, or solid. Examples: Oxygen in water, ethanol in water, glucose in water.
• Solid Solutions: Solute can be gas, liquid, or solid. Examples: Hydrogen in palladium, amalgam of mercury and sodium, copper in gold.

Expressing Concentration

• Mass Percentage (w/w): Mass of solute per total solution mass.
• Volume Percentage (v/v): Volume of solute per total solution volume.
• Mass by Volume Percentage (w/V): Mass of solute per 100 mL solution.
• Parts Per Million (ppm): Used for trace quantities.
• Mole Fraction: Ratio of moles of one component to total moles.
• Molarity (M): Moles of solute per liter of solution.
• Molality (m): Moles of solute per kg of solvent.

Solubility

• Solubility of solids and gases affected by nature, temperature, and pressure.
• Effect of Temperature: Solubility of solids may increase or decrease.
• Effect of Pressure: Significant for gases, not solids.
• Henry’s Law: Solubility of gas is proportional to its partial pressure.

Raoult’s Law

• Deals with vapor pressures of liquid solutions.
• Ideal Solutions: Follow Raoult's law; no enthalpy or volume change upon mixing.
• Non-Ideal Solutions: Show positive or negative deviations from Raoult's law.
• Azeotropes: Mixtures with constant boiling points.

Colligative Properties

• Depend on the number of solute particles.
• Lowering of Vapor Pressure: Relative lowering equals mole fraction of solute.
• Elevation of Boiling Point: Boiling point increases with solute addition.
• Depression of Freezing Point: Freezing point decreases with solute addition.
• Osmosis and Osmotic Pressure: Solvent flow through semi-permeable membranes.

Abnormal Molar Masses

• Dissociation: Leads to lower apparent molar mass.
• Association: Leads to higher apparent molar mass.
• van’t Hoff Factor (i): Accounts for dissociation or association effects.

Applications and Examples

• Calculation examples for molarity, molality, and colligative properties.
• Real-world applications like IV solutions, antifreeze, and osmotic processes.

Summary

• Solutions are critical in chemistry, with properties influenced by solute-solvent interactions.
• Understanding the principles of solubility, concentration, and colligative properties is essential.