Separation Techniques in Chemistry

Separation Techniques

• Sieving separates mixtures of different particle sizes, like sand and gravel.
• Sublimation is a phase change where a solid directly turns into a gas without becoming a liquid.
  • Examples include ammonium chloride (NH4Cl), naphthalene, menthol, and dry ice.
• Magnetization separates magnetic substances from non-magnetic ones.
• Filtration separates an insoluble solid from a liquid.
  • The solid retained on the filter paper is the residue.
  • The liquid passing through is the filtrate.
• Decantation involves carefully pouring off a liquid from a solid, often using a glass rod.
• Centrifugation spins a mixture in a centrifuge to separate an insoluble solid from a liquid.
• Evaporation to dryness recovers a solid from a solution by evaporating the liquid.
• Crystallization recovers a pure dissolved solid from a solution.
  • Techniques include adding a seed crystal, scratching the container, shaking, or using a nucleation site.
• Precipitation separates an insoluble solid from a solution using a precipitating agent.
  • This agent forms a precipitate which can be separated via filtration or decantation.

Simple Distillation

• Separates miscible liquids with boiling points differing by at least 25°C.
• Example: Separating water and ethanol.

Fractional Distillation

• Separates miscible liquids with boiling points closer than 25°C.
• Example: Separating gasoline from crude oil.

Chromatography

• Separates substances based on different movement rates along a medium (paper or gel).
• Separates colored and colorless substances.
• Types include: Absorption, Partition, Paper, Column, Thin Layer, Gas-Liquid, and Gas-Solid Chromatography.

Examples of Chromatography

• Separates ink and chlorophyll components.
• Chlorophyll's major constituent is magnesium.
• Blue ink's chemical formula is C37H29N3O9S3.
• Chlorophyll's chemical formula is C55H72MgN4O5.

Separating Funnel Method

• Separates immiscible liquids, like water and oil.

Recrystallization

• Purifies an impure solid sample.

Determination of Purity of a Substance

• Techniques include:
  • Visual Inspection: Observing color and appearance.
  • Inhalation (Olfaction): Detecting odors.
  • Boiling and Melting Point Determination: Pure substances have sharp melting/boiling points; impure ones have ranges.
  • Mixed Melting Point Method: Mixing a pure sample with an unknown; a sharp melting point suggests purity; a wide range indicates impurity.
  • Refractometry: Measuring refractive index to compare with literature values for pure substance.