Separation techniques

There are many different physical methods used to separate a wide variety of mixtures. The physical methods are as follows;

Types of separation techniques

1. Sieving: 

It is a method of separating solid particles of different sizes. This method can found in mining and garri production

2. Decantation: 

Source: www.en.wikipedia.org 

It is a method that is used to separate a mixture of liquid and denser solid particles which separate into two two distinct layers on standing. Decantation is an inaccurate method of separation but saves time.

3. Filtration: 

Source: www.brainly.in 

it has to do with the separation of insoluble particles from liquids through the pores of the filter paper. During filtration, the liquid portion passes through the filter paper, while the solid material remains on the filter paper. E.g separation of chalk dust in water.

4. Evaporation: 

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It is the process of vapourisation of a liquid at all temperatures. With the high heat of the Bunsen flame, evaporation may be difficult to control, as solution may spatter and the solid may decompose. Evaporation is used in salt making industries.

5. Distillation: 

Source: www.123rf.com 

it used to recover a solvent from a solution. In other words, it is a process of vaporizing a liquid and then condensing the vapour. Distillation can be used to purify liquids and in gin distilleries.

6. Fractional distillation:

 Source: www.energyeducation.ca 

it used to separate a mixture of two or more mixed liquids with close boiling points into its component fractions. Fractional distillation can be used to recover important fractions from petroleum such as natural gases, petrol, kerosene, gas oil, heavy oil and bitumen.

7. Crystallization: 

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crystallization is used to separate salts which decompose easily on heating from their solutions. The salt crystals gotten from it are pure and they contain water of crystallization.e.g copper (II) tetraoxosulphate (VI) pentahydrate CuSO₄. 5H₂O etc. This method is used in the manufacture of drugs and sugar where purity of the product is important

8. Sublimation: 

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The vapours of certain substances, when cooled, condense directly to become solid. These solids, when heated, also change directly to the gaseous state without going through the liquid state.

9. Precipitation: 

Source: www.commons.wikimedia.org 

is a process that involves the mixing of two different solutions which react to produce one soluble compound and an insoluble substance called the precipitate, e.g when a solution of sodium chloride, is added to a solution of silver trioxonitrate (v), a soluble sodium trioxonitrate (v) and an insoluble silver chloride are formed. NaCL_(aq)+AgNO_3(aq) > AgCL_(s)+NaNO_3(aq)

10. Chromatography: 

Source: www.en.wikipedia.org 

It is a means of separation and analysis that utilizes fractional separation. It is based on the principle that if a fluid containing a number of substances is allowed to pass through an absorbing medium, the different substances in the fluid may travel at different rates and be separated. Two advantages of chromatography are; (i) it can be performed with very small masses of the material and (ii) the substances are not destroyed in the process.

11. Separating funnel method: 

Source: www.goodscience.com.au 

it is used to separate two or more liquids which cannot mix together to form a single liquid.

12. Magnetic separation: 

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magnetic substances are separated from non-magnetic particles in a mixture by a magnet. This method is used in the steel industry and also to remove magnetic impurities from Tin ore.

Note: that impurities lower the boiling point of a substance and raise its boiling point.

Properties of pure substances

(I) melting point and boiling point: the melting point and the boiling point of a given pure substance is fixed at a particular temperature and can be determined.

(II) density: the density of a substance is a physical property. Every pure substance has its definite density.

Past questions

1.Sugar is separated from its impurities by? (Jamb 2005) 

A. Distillation

B. Evaporation

C. Precipitation

D. Crystallization

Answer: D

2. A mixture of petrol and water can be separated through? (Jamb 2007)

A. The use of filter paper

B. The use of a separating funnel

C. Centrifugation

D. Distillation

Answer: B

Solution: mixture of petrol and water can be separated through the separating funnel because they do not mix together to form a single liquid.

3. Chlorophyll obtained from green leaves of plants can be shown to be composed of more than one coloured component by the technique of ? (Jamb 2008)

A. Crystallization

B. Hydrolysis

C. Chromatography

D. Sublimation

Answer: C

4. A mixture of sugar and sulphur can be separated by? (Jamb 2009)

A. Dissolution in water, evaporation and filtration

B. Filtration, evaporation and dissolution in water

C. Dissolution in water, filtration and evaporation

D. Evaporation, dissolution in water and filtration

Answer: C

Solution: this is as a result that sulphur is insoluble in water and sugar on the other hand is soluble in water.

5. In which of the following separation methods does chemical reaction occur?

(a) Chromatography (b) sublimation (c) precipitation (d) distillation

Answer: C

6. Pure solvent is obtained by ?

(a) Evaporation (b) extraction (c) condensation (d) distillation

Answer: D

7. The constituents of leaf pigment can be separated by ? 

(a)Chromatography (b) filtration (c) fractional crystallization (d) fractional distillation

Answer: A

8. When a solid substance changes directly to a gas on heating without passing through the liquid state, the substance is said to have undergone?

(a)Crystallization (b) evaporation (c) melting (d) sublimation

Answer: D