(40) GCSE Chemistry Revision "Filtration and Crystallisation"

Physical Separation Techniques

Physical separation techniques are methods used to separate mixtures but cannot separate the elements in a compound.

1. Overview

• Designed to separate mixtures, not compounds.

• Compounds require chemical reactions (e.g., reduction, electrolysis) for their separation.

2. Filtration

• Definition: A method used to separate an insoluble solid from a liquid.

• Key Term: Insoluble - means the solid does not dissolve in the liquid.

• Example:

  • Silver Chloride and Water:

    • Silver chloride (AgCl) is solid (S) and does not dissolve in water (L).

    • When mixed, silver chloride is suspended in liquid water.

    • Process:

      • Use a filter funnel and filter paper.

      • Pour the mixture into the paper; water passes through, collecting as "filtrate."

      • Silver chloride remains on the filter paper (trapped).

• Outcome: The method successfully separates the insoluble solid (silver chloride) from the liquid (water).

3. Crystallization

• Definition: A technique to separate a soluble solid from a liquid.

• Key Term: Soluble - means the solid can dissolve in the liquid.

• Example:

  • Sodium Chloride and Water:

    • Sodium chloride (NaCl) is soluble in water (forming an aqueous solution). State symbol: AQ.

    • Upon evaporation of water, sodium chloride crystallizes out.

    • Crystallization can be sped up by gently heating the solution, but care should be taken not to decompose sensitive substances.

• Outcome: The process leaves behind solid crystals of sodium chloride after the liquid has evaporated.

4. Summary of Techniques

• Filtration effectively separates insoluble solids from liquids.

• Crystallization is used to separate soluble solids from liquids, commonly yielding pure solid samples after evaporation.