Methods of Purification

Purification methods are used to separate and purify substances from mixtures. The key techniques you need to know include:

1. Filtration

• Purpose: To separate an insoluble solid from a liquid.
• Process:
  • A mixture of solid and liquid is poured through filter paper placed in a funnel.
  • The solid (residue) stays on the paper.
  • The liquid (filtrate) passes through and is collected below.
• Example: Separating sand from water.

2. Crystallization

• Purpose: To obtain a pure solid from a solution.
• Process:
  • Heat the solution gently until it becomes saturated (no more solute can dissolve).
  • Cool the solution slowly.
  • Crystals form as the solubility of the solute decreases with temperature.
  • Filter the crystals and dry them.
• Note: This method is ideal for substances that decompose on strong heating (unlike evaporation to dryness).

3. Simple Distillation

• Purpose: To separate a solvent from a solution.
• Process:
  • Heat the solution until the solvent boils and turns into vapor.
  • The vapor passes through a condenser where it cools and condenses back into a liquid.
  • The pure solvent is collected in a separate container.
• Example: Obtaining pure water from saltwater.

4. Fractional Distillation

• Purpose: To separate two or more miscible liquids with different boiling points.
• Process:
  • The mixture is heated in a distillation flask.
  • Vapors rise and enter a fractionating column that allows only vapors with lower boiling points to pass through.
  • Each component is collected at its specific boiling point.
• Example: Separating ethanol from water.

5. Paper Chromatography

• Purpose: To separate soluble substances, usually colored dyes or inks.
• Process:
  • Place a drop of the mixture on filter paper.
  • Dip the bottom edge of the paper in a suitable solvent (e.g., water or ethanol).
  • As the solvent rises, it carries the components at different rates.
  • Different spots will appear for different substances.
• Applications: Identifying food dyes, testing for purity.

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