TOPIC: STANDARD SEPARATION TECHNIQUE
STANDARD SEPARATION TECHNIQUES
These are the various methods that are available and used to separate components of a mixture from the mixture. they include the following methods discussed below
1. SIEVING
This is used to separate solid particles of different sizes. Particles smaller than the size of the sieve (mesh) pass through leaving behind particles of larger sizes. It is used in gold and diamond mines and in garri industries.
2. MAGNETIC SEPARATION
This method is used to separate magnetic substances from non-magnetic particles. It makes use of a magnet. An example is the separation of a mixture of iron filings or pins and sugar.
It is used in mining and steel industries. It can be used to remove magnetic impurities from tin ores. It can be used to separate iron filings from sulphur powder.
3. FILTRATION
Filtration is a separation technique that involves separating an insoluble solid from a liquid using a filter. For example, a mixture of chalk particles in water can be separated using filtration technique.
Filtration is used in industries such as water purification plants and breweries
4. CENTRIFUGATION:
Centrifugation
is a standard separation technique used to separate a mixture of insoluble
solid from liquid by using a centrifuge. A centrifuge is a machine which can
spin test tubes containing suspensions at high speed. Centrifugation is often
used when there is only a small amount of material. In hospitals, blood samples
are centrifuged to separate the blood cells from the plasma.
5. DECANTATION
Decantation is a separation technique used to separate a mixture containing insoluble solid from a liquid. This is done when the mixture is allowed to settle down with the upper clear liquid carefully poured or decanted into a clean container thereby leaving the lower solid in the container originally containing the mixture. This is a quick but inaccurate method of separating the components of a mixture.
6. EVAPORATION
Evaporation is a separation technique used to recover soluble solute from its solvent. For example, salt can be separated from salt solution by evaporation.
Evaporation is used in salt –making industries.
7. CRYSTALLIZATION
Crystallization is used to obtain pure crystals of salts which decompose easily on heating, from its solution.
The solution is concentrated by heating until it is concentrated, and it is then allowed to cool down, the crystals start to form as the solution cools down. To induce crystal formation:
(i). some crystals of the salt are added (seedling)
(ii). use a glass rod to scratch the inside of the container.
Crystallization is used in drug industries and sugar industries, industries where purity of a substance is important.
8. FRACTIONAL CRYSTALLIZATION
It is used to separate two or more solutes (solids) which are present in the same solution. The solutes to be separated must have different solubilities at different temperatures. Starting from a particular temperature, as cooling of the solution begins the solutes that is least soluble begins to appear, that is, the crystals that are least soluble at that particular temperature begins to crystalize out leaving the more soluble salts in the solution.
9. PRECIPITATION
In precipitation, a difference in the solubility of a solid in two different miscible liquids is used. For example, FeS04 is soluble in water but not on ethanol. If ethanol is added to a solution of FeS04 in water, the FeS04 will be precipitated out of the solution and filtered out.
10. SUBLIMATION
Sublimation is the change of state from solid to gas directly on application of heat. Examples of substances that sublime are iodine and ammonium chloride. Sublimation can be used to separate these substances. The pure crystal recovered is the sublimate.
11. DISTILLATION
This method is used to recover a solvent from a solution. It involves heating the liquid until it vapourizes and then condensing the vapour with the aid of a condenser into a liquid called distillate. The solute and other impurities remain in the distillation flask. This method is used in gin/brandy and water distilleries to manufacture gin and distilled water.
FRACTIONAL DISTILLATION
This method is used to separate a mixture of two or more miscible liquids with close boiling points. When two liquids have boiling points that are very close (less than 10oC ) it becomes difficult to use simple distillation. A fractionating column is inserted into the distillation flask.the fractionating column does the actual separation
How the fractionating column works: - As the mixture boils and enters the fractionating column, the vapours loss their heat to the glass beads in the fractionating column and falls back into the mixture, (i.e by returning components whose boiling point is less than that of the fractionating column). Only components whose boiling point is the same as the fractionating column are allowed to pass into the condenser. This method is used in the refinery to separate crude oil into its various fractions, also the extraction of oxygen and nitrogen from Liquified air, the manufacture of ethanol and to separate benzene and methyl benzene mixture.
SEPARATING FUNNEL
This method is used to separate a mixture of two immiscible liquids or a polar liquid from a non-polar liquid. It depends on the densities of the two liquids. The less dense liquid will float on top and the denser below. It is used to separate water and kerosene
CHROMATOGRAPHY
This method uses a solvent moving over an adsorbent medium (paper) which is porous to separate mixtures of solutes.
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A chemist uses liquid chromatography to analyze a complex mixture of substances. The chromatograph utilizes an adsorptive medium, which when placed in contact with a sample, adsorbs the various constituents of the sample at different rates. In this manner, the components of a mixture are separated. Chromatography has many valuable applications, such as determining the level of pollutants in air, analyzing drugs, and testing blood and urine samples. |
Types
1. Paper chromatography
2. Thin layer chromatography
3. Gas chromatography
4. Column chromatography
In paper chromatography, a solution, such as ink, is spotted into the paper (stationary phase) near one end. The paper is then dipped into an appropriate solvent such as water or ethanol (mobile phase) in a closed air-tight jar. The solvent moves up the paper and separates the substance into various spots.The paper is removed and dried. The different spots on the paper show the different constituents the substance (ink, dye or chlorophyl) contains.
USES
i). It is used in medicine to analyze blood.
ii). It is used in the industry to identify petroleum fractions.
iii). It is used in scientific research.
CRITERIA FOR PURITY
1. The melting point and boiling point of a pure substance are fixed but change in the presence of impurities. Impurities lower the melting point of a substance and increase its boiling point.
And the criteria for purity is
1. Sharp melting point: substance must melt at a specific temperature
2. Sharp boiling point: substance must boil at a specific temperature called the boiling point.
3. Substance must have a constant density
4. Substance must show only one spot on a chromatographic plate.
OBJECTIVE QUESTIONS
1. A mixture of oil and water can be separated by
(a) sublimation
(b) evaporation to dryness
(c) using a separating funnel
(d) fractional distillation
2. Fractional distillation is used to separate
(a) an insoluble substance from a soluble volatile substance
(b) liquids with differing boiling points
(c) gas, liquid or solid impurities from a mixture
(d) liquid with close boiling points
3. Which of the following separating techniques can be used to separate a mixture of iodine and sodium chloride?
(a) distillation
(b) evaporation
(c) sublimation
(d) decantation
4. Which of the following is not a type of chromatography?
(a) thin layer
(b) gas
(c) paper
(d) glass
5. Which of the following is a quick but inaccurate way of separating mixture?
(a) decantation (b) evaporation (c) filtration (d) distillation
6. How can you separate a mixture of iron filings and sulphur powder?
(a) distillation
(b) chromatography
(c) magnetization
(d) evaporation
20. A sample of orange juice is suspected to have been contaminated with a yellow dye. Which of
the following methods can be used to detect the dye.
a). Decantation
b). Chromatography
c). Distillation
d). Evaporation
THEORY
1.(a) The diagrams labelled I to IV below illustrate different laboratory set-ups used in the separation of mixtures.
i). Name the separation technique illustrated by each diagram
ii). Which of the set-ups is used for concentrating dilute salt solutions, for the purpose of crystallization
iii). Which of the set-ups is used in obtaining pure water from muddy water?
iv). Mention the set-up you would use to separate a polar solvent from a non-polar solvent
v). State the modification you would make to the set-up labelled IV in order to use it for separating a mixture of NaCl and NH4Cl [waec]
2. The set-up shown in the diagram below was used to separate a drop of universal indicator into the constituent dyes using ethyl ethanoate as the solvent.
(a) what name is given to the separation technique illustrated in the diagram?
(b) State:
(i). How many components are resolved in the separation
(ii). The material normally used in the laboratory as the absorbent medium.
(iii) Which of the labels indicate the point of application of the indicator.
1. Explain the following separation techniques. Magnetic separation, paper chromatography and sieving
2. Describe how you would separate a mixture of NaCl, PbCl2 and NH4Cl
3. What method can be applied to separate a mixture of iron filings and sulphur
4. Mention two criteria for purity of a substance.
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