Separating Solids from Liquids

Key Concepts

• Mixture: A combination of a liquid and an insoluble solid (e.g., sand in water).
• Solution: A liquid with a soluble solid dissolved in it (e.g., sodium chloride in water).
  • Solute: The dissolved solid.
  • Solvent: The liquid in which the solute dissolves.

Techniques for Separation

1. Filtration

• Purpose: Separates insoluble solids from liquids.
• Method:
  • Use filter paper with tiny holes to let liquid through but trap solids.
  • Place filter paper in a filter funnel.
• Analogy: Similar to using a sieve in cooking.

2. Evaporation

• Purpose: Separates soluble solids from liquids by evaporating the solvent.
• Method:
  • Place solution in an evaporating dish or crucible on a tripod.
  • Heat slowly with a Bunsen burner.
  • As solvent evaporates, solution becomes concentrated.
  • Crystals form when it becomes highly concentrated.
  • Eventually, the solvent disappears, leaving dry crystals.
• Advantages: Quick and easy.
• Disadvantages: Solids susceptible to thermal decomposition may break down.

3. Crystallization

• Purpose: Separates soluble solids from liquids without thermal decomposition.
• Method:
  • Place solution in an evaporation dish; heat gently (use a water bath).
  • Stop heating when crystals start to form; let the solution cool.
  • More crystals form as the solution cools (solids are less soluble at lower temperatures).
  • Filter out crystals using filter paper and a funnel.
  • Dry crystals by leaving them warm or in an oven.

Conclusion

• These techniques allow the separation of both soluble and insoluble solids from liquids.
• Choose the appropriate method based on whether the solid is soluble and susceptible to thermal decomposition.