Separation Techniques

Separating mixtures into their pure components is crucial since most substances are used in their pure form. There are various standard techniques used for this purpose.

Common Separation Techniques

Filtration

This technique separates an insoluble solid from a liquid using a filter. For example, chalk particles can be filtered out of water. It is commonly used in water treatment and brewing industries.

Centrifugation

Used to separate insoluble solids from liquids by spinning the mixture at high speed in a centrifuge. It is useful for small quantities and is widely used in hospitals to separate blood components.

Decantation

This involves allowing a mixture to settle and then carefully pouring off the liquid, leaving the solid behind. It is a fast but less accurate method of separation.

Evaporation

Used to recover a dissolved solute from a solution by heating. For example, salt can be obtained from saltwater through evaporation.

Crystallization

Crystallization is used to obtain pure salt crystals that may decompose if strongly heated. The solution is concentrated by heating and allowed to cool so crystals form. To initiate crystal formation:

Common in drug and sugar industries.

Fractional Crystallization

This separates two or more solutes with different solubilities. As the solution cools, solutes crystallize one after the other based on their solubility at different temperatures.

Precipitation

Used when a solute is soluble in one solvent but not another. For example, FeSO4 is soluble in water but not in ethanol. Adding ethanol causes FeSO4 to precipitate and it can be filtered out.

Sublimation

Sublimation involves direct change of a solid to gas upon heating. Substances like iodine and ammonium chloride can be separated by this method. The purified substance collected is called the sublimate.

Distillation

This technique recovers a solvent by heating the solution until the solvent vaporizes, then condensing the vapor back into a liquid (called the distillate). Used in producing distilled water and gin.

Fractional Distillation

Used to separate a mixture of miscible liquids based on boiling point differences. A fractionating column is used when boiling points are close (less than 100°C apart). Applications include:

Separating Funnel

Used for separating immiscible liquids based on their densities. The denser liquid settles at the bottom and is drained off. For example, water and kerosene can be separated using this method.

Sieving

This method separates solids of different sizes. Smaller particles pass through the mesh while larger ones remain. It is used in gold and diamond mining and in processing garri.

Magnetic Separation

This technique removes magnetic materials from non-magnetic ones. It's used in mining, steel production, and in separating iron filings from sulphur powder.

Chromatography

This separation uses a moving solvent and an adsorbent medium like paper to separate mixtures of solutes.

Types of Chromatography:

In paper chromatography, a spot of ink is placed near the edge of filter paper, which is then placed in a suitable solvent. The solvent rises through the paper and separates the mixture into different spots. This is used in blood analysis, petroleum testing, and research.

Criteria for Purity

  1. Pure substances have sharp, fixed melting and boiling points. Impurities lower melting points and raise boiling points.
  2. A pure substance shows a single spot on a paper chromatogram.