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HomeworkScienceChemistry → Separation Techniques

The key to separating mixtures is to find something that one part of the mixture does but the other doesn't. This relies on their physical properties.

  1. Sublimation

    This is the name given to the process where a substance changes straight from a solid to a gas missing out the liquid stage. Sublimation is found in relatively few chemicals, for example iodine, carbon dioxide, and ammonium chloride. Iodine therefore cannot exist as a liquid: It is either a solid or a gas. Don't get confused: liquid iodine solution is iodine dissolved in a solvent such as alcohol or potassium iodide.

    The iodine sublimed into a purple vapour and then condensed at the top, away from the sand.

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  2. Magnetism

    Magnets are used in everyday life for doorbells, car lifting, trains, and doors. A mixture of sulphur and iron filings can be separated using a magnet.

    Dragging the magnet up the side separates the iron filings from the sulphur.

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  3. Density

    If a mixture of oil and water is shaken up and then allowed to settle, the oil rises to the top and separates from the water below. This is because the oil is less dense than the water. By using a separating funnel the water can be drained off first followed by the water.

    Other liquids could also be separated by this method.

  4. Chromatography

    This is a technique that can be used to separate small quantities of two or more soluble solids. This method depends on how well these solids dissolve in a solvent. Each substance has its own solubility.

    Analyzing the dyes present in food colouring
    The water acts as a solvent to the dyes present in the food colouring. As the water spreads up the chromatography paper it dissloves the dyes and carries them along. The larger dye molecules only travel as small distance as they are the least soluble. The smallest particles are carried the furthest and are the most soluble. Each size of particle is a different colour and so a range of colours appears.

    To carry out the experiment simply place a dot of the test substance (e.g. a washable pen) on the dotted pencil mark. If the pen is not washable you can use ethanol instead of water.

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