TYPES OF CHROMATOGRAPHY  
There are three types of chromatography  
(i) Paper chromatography (ii) Thin layer chromatography (iii) Gas chromatography.  
In paper chromatography, the stationary phase is a uniform absorbent paper. The  
mobile phase is a suitable liquid solvent or mixture of solvent.  
The components move with different speeds and thus get separated. The mixture of  
different colours is separated by this method.  
Example separation of black ink by paper chromatography method  
ACTIVITY  
Aim: To carry out simple paper chromatography.  
Requirements: Filter paper, beakers, ink extracts from leaves, acetone or ethanol,  
and watch glass  
Procedure  
1. Take a rectangular piece of filter paper of a size that can fit in a beaker when  
placed upright.  
2. Draw two straight lines one at the base and another at the upper part.  
3. Mark three areas on the base line, and on each mark put a drop of different plant  
extracts. Label the spots A, B, and C, and make sure there is space between the  
spots.  
4. Place the paper, baseline first, into a beaker containing acetone or ethanol and  
cover with a watch glass.  
5. When the acetone or ethanol has risen to the top of the paper, remove the paper  
from the beaker and place it in a dry beaker. Leave it to stand for about 30  
minutes.  
6. Mark the levels to which the pigments have risen for each spot.  
Questions  
1. What is the role of the acetone or ethanol in this experiment?  
2. Can the type and quality of paper influence the separation results? Explain  
Uses of chromatography  
The method of chromatography is used in many different ways, mostly for  
separation of components of mixture, identification and quantification of  
different chemical substances.  
Some of the areas in which chromatography are used are summarized below;  
AREA  
USES  
Medicine  
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Study blood cells.  
Detect types of drugs in blood  
Test for water pollution, soil pollution and air pollution.  
Testing for food contamination  
Analyse blood in crime scenes.  
Detect different fibres  
Health and  
environment  
Security  
Drug testing  
Industries  
Testing quality of products  
Testing shelf-life of food substances.  
Purification of substances  
Test purity or composition of organic substances  
Separate mixtures  
Chemistry  
Biology  
Protein analysis  
Enzyme analysis  
Plasma analysis  
8. SOLVENT EXTRACTION  
Solvent extraction is a process of separating components of a mixture using a  
solvent that dissolves selected components  
For example, extracting essential oils from plant seeds using a liquid that dissolves  
the oils.  
Note: In solvent extraction, the following conditions should be considered when  
choosing a solvent.  
(a) The chosen solvent should dissolve the component of interest  
(b) The solvent must not react with the component of interest  
(c) The solvent chosen should be easily separated from component of interest  
(d) It must not be toxic or corrosive  
Separation Application of Solvent  
(i) It is used to extract cooking oil from seeds or nuts. Example, oil from ground nuts,  
coconuts, cotton seeds, sunflower.  
(ii) It is used to extract tea component from tea leaves using hot water during  
preparation of tea.  
9. MAGNETIZATION (MAGNETIC SEPARATION)  
Magnetization is a process of separating iron (magnetic material) from a mixture  
where by magnetic material is attracted to magnet and leaves behind other  
components of mixture.  
This method is used to separate scrap iron from other metals. Example, a mixture of  
iron and sand, iron and sulphur.  
Figure: Separation of iron and sand and salt (common salt)  
10. Winnowing  
Winnowing is a method used to separate chaff from grain under the influence of  
wind. This is mostly applied in purifying different grains to remove the unwanted  
materials. Examples, Maize and husks, Rice and husks.  
11. Sieving  
Sieving is a method used to separate materials based on their particle size.  
It involves passing a mixture through a sieve, which is a mesh or perforated surface  
with openings of a specific size. Example, a sieve for maize flour.  
12. CENTRIFUGATION  
A centrifuge is a device used to separate small amounts of suspension.  
Centrifugation is a process of separating substances with different densities within  
a liquid or suspension using centrifugal force. It is used when the very small solid  
particles spread throughout the liquid.  
Mechanism of centrifugation process  
In centrifugation, test tubes containing suspensions are spun round very fast. The  
solid gets thrown to the bottom. Huge centrifugal force acting on the particles due to  
the high speed spinning of the samples makes the particles to settle at the bottom  
13. CRYSTALLIZATION  
Crystallization is a process of separating a pure solid substance from a solution by  
warming (boiling a solution in an open container). When allowed to cool the solid will  
be formed as crystals.  
This process involves evaporation but the speed of evaporation is much slower.  
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Crystallization is a process of forming crystals from a super saturated solution when  
left to cool.  
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Crystallization point is the temperature at which crystals form.  
Application of crystallization  
Used in sugar and salt industry to obtain sugar and salt crystals.  
Example, a method is used to extract salt from the sea. Salty sea water is placed in  
wide basins and put in the sun. Water evaporates off, leaving the salt crystals in  
basin.  
14. HAND PICKING  
Hand picking is a method used to separate a mixture of components which are  
large enough to be picked by hand.  
Example: (i) Oranges and Mangoes (ii) Rice and sand  
SIGNIFICANCE OF SEPARATING MIXTURES  
(i)  
Used in softening water. Example, Simple distillation  
Used in breweries. Example, Distillation process  
(ii)  
(iii)  
(iv)  
(v)  
Used in obtaining cooking oil from plants. Example, Solvent extraction.  
Used in refinery industries. Example, Fractional distillation  
Used in removing impurities from metal ores during extraction. Example,  
evaporation and distillation.  
(vi)  
Used in medical diagnosis. Example, Chromatography and centrifugation  
Used in security for crime detection. Example, chromatography  
(vii)  
(viii) Used in purification of water. Example, Filtration  
(ix)  
(x)  
Used in water treatment system. Example, Decantation  
Used in chemical analysis and tests. Example, Chromatography  
REVISION EXERCISE FIVE  
1. (a) Give any six (6) methods available for the separation of mixtures.  
(b) Name the process that can be used to separate the following substances:  
(i) Iodine and iron  
(ii) Salt and sugar  
(iii) Salt and sand  
(iv Kerosene and water  
(vi) Iron and mud  
(v Water and ethanol  
(vii) Water and flour  
(ix) Rice grains and husks  
(viii) Water and mud  
2. In a tabular form, give the differences between a physical and a chemical  
change.  
3. Indicate, giving examples in each case, which of the following can be described as  
physical or chemical changes:  
(a) The heating of a salt solution  
(c) The burning of paper or wood in air  
(e) Fermentation of milk  
(b) The action of heat on ice  
(d) The rusting of iron in air  
(f) The melting of a metal  
4. Differentiate between a homogenous mixture and a heterogeneous mixture.  
5. Briefly explain how you can differentiate a solution and a suspension by their  
appearance.  
6. What role does the knowledge on boiling point play in distillation process?  
7. What factors determine the choice of a specific separation method for a given  
mixture?  
8. How are the suspensions utilized in the food and beverage industry?  
9. Write TRUE for statements that are correct and FALSE for statements that are  
not correct.  
(a) Matter exists in three states namely, solid, liquid and gas.  
(b) A liquid has no fixed volume.  
(c) A change in state from gas to solid is called sublimation.  
(d) In a physical change, a new substance is usually formed.  
(e) Metals are shine and can be polished.  
(f) The components of a compound can be separated by physical means only.  
(g) The liquid state is one in which the particles are moving freely in all directions.  
(h) Condensation is the same as solidification.  
(i) Boiling occurs at one particular temperature.  
(j) Iodine sublimes when heated.  
10. Suppose you are given a mixture and you are asked to determine whether it is  
homogeneous or heterogeneous.  
(a) What could be your criteria for the analysis?  
(b) Make a description of how you will separate the;  
(i) homogeneous mixtures.  
(ii) heterogeneous mixtures.  
11. Provide examples of how chromatography is used in the analysis of  
pharamaceuticals.  
12. Describe the applications of solutions, suspensions and emulsions in daily life  
13. The time taken for sugar to dissolve in cold tea differs from that in hot tea.  
Explain.  
14. Why can the saturated sugar solution dissolve more sugar after being heated?  
15. Are the formations of homogeneous colourless solutions always physical  
changes? Explain your answer.  
16. Describe two examples where simple distillation is used in daily life.  
17. David bought some salt and sugar from the shop. On his way back home, he  
accidentally dropped them on the ground. Sugar, salt and sand were mixed  
together. He collected the mixture and took it to the school laboratory the next  
day to separate them from sand. Explain in detail the experimental methods he  
could use to obtain and recover salt and sugar separately.  
18. (a) In the following diagram label letters P, Q and Z  
(b) Give the name of the process represented by the diagram.  
(c) State the role of glass beads in the set-up.  
19. When clean water is mixed with dirty and contaminated sand forms muddy  
water. Muddy water can be separated by decantation, simple distillation or  
filtration methods. With reason for each you make, briefly explain which  
method is; (a) Best method (b) Better method (c) Good method  
20. Below is a diagram for separating a mixture of water and ethanol in the  
laboratory. However, the diagram has been drawn wrongly and some parts have  
been labeled incorrectly. Study the diagram carefully and then answer the  
subsequent questions.  
(a) With reasons, identify five (5) mistakes from the diagram above  
(b) Re-draw a well labeled diagram to represent the process of separating a  
mixture of water (with boiling point of 100 oC) and ethanol (with boiling  
point of 78.4 oC).  
(c) Give the meaning of the process represented by the diagram in (b) above.