01.07 Solutions

What is a Solution?

• Definition: A solution is a homogeneous mixture where one or more substances (solutes) are uniformly dispersed within another substance (solvent).
• Common Example: Saltwater, where salt (solute) is dissolved in water (solvent).

Prevalence of Solutions

• Earth’s Surface: Approximately two-thirds covered by solutions, mainly various salts dissolved in water (seawater).
• Seawater Components:
  • Salts: Completely dispersed; cannot be seen.
  • Dissolved Gases: Oxygen (O₂) and carbon dioxide (CO₂) essential for marine life.

Types of Solutions

• Solid in Liquid: e.g., Salt in water.
• Gas in Liquid: e.g., Oxygen and carbon dioxide in seawater.
• Liquid in Liquid: e.g., Alcohol in water.
• Metal in Metal (Alloys): e.g., Solder (tin and lead).

2. Solvents and Solubility

Common Solvents

• Water: The most common solvent due to its polar nature.
• Organic Solvents:
  • Examples: Ethanol, propanone (acetone), trichloroethane.
  • Importance: Dissolve substances that are insoluble in water.

Solubility Terms

• Soluble: A solute that can dissolve in a particular solvent.
  • Example: Sugar is soluble in water.
• Insoluble: A substance that does not dissolve in a particular solvent.
  • Example: Sand is insoluble in water.
• Miscible: Two liquids that form a completely uniform mixture.
  • Example: Alcohol and water are miscible.

Alloys

• Definition: Mixtures of metals, often referred to as solutions in the liquid state before solidifying.
• Example: Solder, an alloy of tin and lead, has a low melting point, making it useful for joining metals.

3. Concentration and Saturation

Concentration of Solutions

• Definition: The amount of solute dissolved in a given quantity of solvent or solution.
• Types:
  • Dilute Solution: Contains a small proportion of solute.
    • Example: A teaspoon of sugar dissolved in a glass of water.
  • Concentrated Solution: Contains a high proportion of solute.
    • Example: A saturated solution where no more solute can dissolve.

Saturated Solutions

• Definition: A solution that contains the maximum amount of dissolved solute at a specific temperature.
• Characteristics:
  • No more solute can dissolve at this temperature.
  • To dissolve more solute, the temperature must be increased.

Solubility and Temperature

• General Trend: The solubility of most solids in liquids increases with an increase in temperature.
  • Example: More sugar can dissolve in hot tea than in iced tea.

Crystallisation

• Process: When a saturated solution is cooled, the solubility decreases, and excess solute crystallizes out of the solution.
  • Example: Sugar crystals forming when hot sugar water cools down.

4. Solubility of Gases in Liquids

Temperature Effect

• Trend: Unlike most solids, the solubility of gases in liquids decreases as the temperature rises.
  • Example: Less oxygen dissolves in warm water compared to cold water.

Pressure Effect

• Trend: The solubility of gases increases with an increase in pressure.
  • Example: Carbon dioxide is more soluble in drinks under pressure, creating sparkling beverages.

Applications and Examples

• Aquatic Life: Sufficient dissolved oxygen in water supports fish and other marine organisms.
• Sparkling Drinks: Contain carbon dioxide dissolved under pressure; they fizz when opened as pressure is released.
• Fizzy Drinks Going Flat: Carbon dioxide escapes when the container is open, especially faster at higher temperatures.

5. Key Terms and Definitions

• Soluble: A solute that can dissolve in a particular solvent.
• Insoluble: A substance that does not dissolve in a particular solvent.
• Miscible: Two liquids that form a completely uniform mixture when combined.
• Alloys: Mixtures of elements (usually metals) designed for specific properties, e.g., solder (tin and lead).
• Saturated Solution: A solution containing the maximum amount of dissolved solute at a specific temperature.
• Concentration: A measure of the amount of solute dissolved in a solvent.
  • Dilute: High proportion of solvent, low proportion of solute.
  • Concentrated: High proportion of solute, low proportion of solvent.
• Solubility: The amount of solute that can dissolve in a solvent at a particular temperature.

6. Examples and Applications

Everyday Examples

• Saltwater: A solution where various salts are dissolved in water, covering most of Earth’s surface.
• Sugar in Tea: Demonstrates concentration, saturation, and crystallization upon cooling.
• Alloys in Jewelry: Gold mixed with other metals to form alloys like white gold.
• Carbonated Beverages: Show solubility of gases under pressure and their release upon opening.

Practical Applications

• Crystallization in Purification: Used to purify substances by dissolving impurities and allowing pure solute to crystallize out.
• Manufacturing of Alloys: Creating metals with desired properties for construction, electronics, and other industries.
• Environmental Impact: Understanding solubility of gases helps in managing oxygen levels in water bodies for marine life.

7. Summary

• Solutions are homogeneous mixtures of solutes and solvents, with water being the most common solvent.
• Solubility depends on the nature of solute and solvent, temperature, and pressure.
• Concentration can vary, leading to dilute, concentrated, or saturated solutions.
• Crystallization occurs when a saturated solution is cooled, causing excess solute to form crystals.
• Gases have unique solubility behaviors, increasing with pressure but decreasing with temperature.
• Alloys are metal solutions with properties tailored for specific uses.