Chemistry Unit 2: Experimental Techniques

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Unit 2.1 Methods of Separation and Purification

1. Describe paper chromatography.

Chromatography is used to separate two or more dissolved solids in a solution. Paper chromatography uses water to separate the solids. A line is draw on a piece of paper and the solution is dotted on that line. After labelling the dot, the piece of paper is placed into water (or another solvent), the water level meeting a place a little below the pencil line. As the water travels up the paper (this is called capillary action), it separates the solids in the solution. 

We can use chromatography to evaluate the contamination of food or water, which is part of health and safety procedures. 

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2. Interpret simple chromatograms.

The further a substance moves up the paper, the more soluble it is. 

3. Describe methods of separation and purification: filtration, crystallisation, distillation, fractional distillation.

Filtration: when you have a solid and solution, filtering the mixture can help you separate each from the other e.g. sand and water

Crystallisation: crystallisation allows you to separate a solute from a solvent. The solution is left to dry or heated up, evaporating the solvent and leaving the solute in the form of crystals e.g. salt and water

Distillation: distillation helps you obtain a pure liquid from a mixture of liquids. The mixture is heated up in a flask, and the liquid with the lower boiling point will evaporate first. The vapour is cooled in the Liebig condenser and collected in the form of a liquid e.g. ethanol and water

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Fractional distillation: this process is similar to distillation, but it is used to separate more parts in a mixture. The mixture is heated up in a flask, and attached above the flask is a column with beads. This helps to separate the different parts as they evaporate. The vapours are then cooled through the Liebig condenser and collected as liquids e.g. crude oil

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4. Understand the importance of purity in substances in everyday life, e.g. foodstuffs and drugs.

As mentioned above, checking the purity of things is important as contamination can result in health and safety issues, especially food or drugs. They can cause you to become very sick.

5. Identify substances and assess their purity from melting point and boiling point information.

Take water for example. We all know that the boiling point of water is 100°c. If the boiling point has changed, this indicates that the water is not pure. This is the same with the melting point.

6. Suggest suitable purification techniques, given information about the substances involved.

With the above methods of separation and purification, I have given some examples of what each method can be used for.