Filtration

This technique is used to separate an insoluble solid from a liquid. (将不可溶解固体从液体中分离)
It can be used to obtain a product that is free from unreacted chemicals, by-products or solvent.
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Decantation 倾析法

the process of separation of liquid from solid and other immiscible (non-mixing) liquids, by removing the liquid layer at the top from the layer of solid or liquid below.
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Evaporation/Crystallisation

One way to separate a soluble solid from its solution is to make crystals. (将溶解的固体与溶液分离)
This involves evaporating the solution to a much smaller volume and then leaving it to cool. As the solution cools, crystals form, and these can be obtained by filtration.
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Simple distillation

Distillation separates a liquid from a solution. (将液体从溶液中分离)

For example, water can be separated from salty water by simple distillation.
This method works because the water evaporates from the solution, but is then cooled and condensed in a condenser and collected in a separate container.
The salt does not evaporate and so it stays behind.

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Fractional Distillation

used when boiling points of the liquids are close and/or a higher degree of purity is required

  • The solution is heated to the temperature of the substance with the lowest boiling point
    • This substance will rise and evaporate first
    • The vapours will pass through a condenser, where they cool and condense
    • The condensed liquid is then collected in a beaker
    • All of the substance is evaporated and collected, leaving behind the other component(s) of the mixture
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Paper chromatography

Chromatography is used to separate substances and provide information to help identify them

  1. The components have different solubilities in a given solvent
  2. A pencil line is drawn on chromatography paper and spots of the sample are placed on it
  3. The paper is then lowered into the solvent container, making sure that the pencil line sits above the level of the solvent so the samples don’t wash into the solvent container
  • A pencil is used for this as graphite is insoluble in water.
  • The solvent used is usually water, ethanol
  • The solvent travels by capillary action, taking some of the coloured substances with it
  • different solubilities , travel at different rates -> spread apart
  • higher solubility -> travel further

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