We separate mixtures in order to obtain the mixture constituents and put them into appropriate use. The world around us is made up of mixtures of different substances. These substances are often of little use when they are in the form of a mixture. For this reason, separation of the individual components of mixtures is deemed inevitable.
1. (i) Fractional distillation.
Is used industrially to separate the various fractions of crude oil such as natural gas, petrol,kerosene, diesel, lubricating oils, waxes, asphalt and bitumen. All these fractions have a
significant use in man's industrial, domestic and commercial activities. The functions or use of all these fractions is well known to everyone of us.
Can you mention the functions of each fraction?
You will learn more about these products in organic chemistry section.
(ii) Chromatography has proved very useful in the analysis of biologically important molecules such as sugars, amino acids, and nucleotide bases. Molecules such as amino acids can be seen if the paper is viewed under ultraviolet light.
(ii) Separation Air Components.Separates the air into its component gases. This is important because these components have many uses in our everyday life. Some of these fractions and their functions are summarized below:2. Filtration and purification of drinking water. This makes use of processes such as decantation, filtration and sometimes distillation. The bottled water we drink is prepared by some or a combination of these processes.3. In Iron Mining.In electromagnet is used to separate magnetic iron ore from other materials in the crushed ore.4. In the manufacture of Ethanol.Done by fermentation in breweries, distillation is used in the final stage to purify ethanol to its purest form (surgical spirit) in which the ethanol is usually sold. Likewise, distillation of fermented starch (8-12% ethanol), yields alcoholic drinks called spirits (whisky, gin, brandy, rum) which contain about 35-40% ethanol.5. Paper chromatography (i) It is very useful in analysis of substances present in a solution. For example, it can tell whether a substance has become contaminated or otherwise. This can be very important, because contamination of food or drinking water, for instance, may be dangerous to our health. |
| Component | Use |
| Nitrogen | Manufacture of fertilizer |
| Oxygen | Used in hospitals, steel making, diving and space travel |
| Argon | Filling light bulbs |
| Carbon dioxide | Fire extinguishing, used in carbonate drinks, etc. |
| Helium | Filling airships and water balloons |
| Krypton and Xenon | Used in photographic flash lamps |
(ii) Chromatography has proved very useful in the analysis of biologically important molecules such as sugars, amino acids, and nucleotide bases. Molecules such as amino acids can be seen if the paper is viewed under ultraviolet light.
(iii) Paper chromatography is the test that can be used to check for the purity of a substance. If the sample is pure, it should only give one spot when run in several different solvents.
6. Checking for Purification.
Other separation methods are also used to check whether purification has been successful.
Samples obtained by distillation can be re-distilled. The purity of crystals can be improved by recrystallisation. A water sample can be tested for amount of dissolved material by evaporating a certain amount of water to dryness.
Samples obtained by distillation can be re-distilled. The purity of crystals can be improved by recrystallisation. A water sample can be tested for amount of dissolved material by evaporating a certain amount of water to dryness.
The solid waste can be weighed. This would give the amount of dissolved solid in the water. The process of purification is of crucial importance in many areas of chemical industry. Medical drugs (pharmaceuticals) must be of highest possible degrees of purity. Any contaminating substances even in very small amounts may have harmful side effects.
7. Centrifugation.
(i) Separation of cream from whole milk is done by the process of centrifugation. As the milk is spun, the heavier contents are forced down and the lighter cream rises up. After centrifugation, the cream is poured off the top by decantation. This is the initial stage of milk constituent separation, after which other components such as milk proteins (cheese) are separated.
(ii) Centrifugation is applicable in blood analysis, where the solid part of blood is separated from the liquid part by centrifugation. Blood is a suspension containing microscopic blood cells (corpuscles) in a liquid called plasma. If blood is centrifuged in a test tube, the blood cells are flung to the bottom, leaving the liquid plasma on top.
8. Extraction of Metal from their Ores.
Knowledge of separation of two immiscible liquids can be applied in the extraction of metals such as iron from their ores. For example, at the base of the blast furnace, the molten slug forms a separate layer on top of the liquid iron. The two can then be "tapped" off separately. The method is very useful in organic chemistry as part of the process called solvent extraction.
9. Salt Production.
Evaporation process is used in the extraction of common salt from seawater whereby the sun evaporates water molecules from salty water, leaving crystals of the salt behind.
10. Layer separation
This technique is applied in the recovery of liquids from contaminants.
11. Extraction of Edible Oils.
Solvent extraction process is applied in the extraction of certain edible oils from seeds, and in the extraction of some metals from sludge mixture.
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