(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.

Designed to separate mixtures, not compounds.
Compounds require chemical reactions (e.g., reduction, electrolysis) for their separation.

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).

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.

Filtration effectively separates insoluble solids from liquids.
Crystallization is used to separate soluble solids from liquids, commonly yielding pure solid samples after evaporation.