SEPARATION OF MIXTURES
Many mixtures need to be separated in order to obtain the useful substances. This is because mixtures contain useful substances mixed with unwanted materials (impurities). The method used to separate mixture depends on the components of the mixture and their properties. Such properties are density, solubility, size, magnetic properties, sublimation, boiling and melting point
METHODS OF SEPARATING MIXTURE
The following are methods used to separate mixtures
(i) Decantation
(ii) Filtration
(iii) Evaporation
(iv) Distillation (v) Layer separation (vi) Sublimation
(vii) Chromatography (viii) Solvent extraction (ix) Winnowing (x) Magnetic separation (Magnetization)
(xi) Centrifugation (xii) Crystallization (xiii) Hand picking (x) Sieving
Principle for separation of mixtures are applied in fields like mining, agriculture and other large-scale industries. For example, decantation, filtration and sedimentation are widely used in purification of water for public consumption.
(1) DECANTATION
By definition: Decantation is the process of separating a heterogeneous mixture of a liquid and solid by pouring out the liquid only and leaving the solid at the bottom of the container
NB:
The process of some components of mixture settling at the bottom is called Sedimentation
Decantation can be used to separate
(i) Water from muddy water, water from mixture of water and sand etc
(ii) Rice and water, beans and water etc
Diagram to show separation of sand and water by decantation (sedimentation)
Separation Application of Decantation
(i) Water treatment systems (ii) Separate of components of blood
(2) FILTRATION
By definition: Filtration is the method of separate heterogeneous mixture of a solid and liquid by using porous filter eg filter paper
NB: (i) Solid that remains on a filter is called residue
(ii) Liquid that pass-through filter is called filtrate
Separation Application of Filtration
(i) Purification of water (ii) Extraction of juice from fruit (iii) Extraction of cream from milk
(3) EVAPORATION
Defn: Evaporation is a method of separating a solute from a liquid solution through heating.
In evaporation solvent is converted from liquid to gas and solute remains as residue.
Example: Mixture of water (solvent) and salt (solute), when heated water evaporates leaving sand behind as residue.
Diagram to show separation of salt and water by evaporation
Other examples of mixtures which can be separated by evaporation are (i) sea water (ii) sugar solution
Separation Application of Evaporation
Evaporation is used in extraction of common salt from sea water
(4) DISTILLATION
Definition: Distillation is a process of separating the components of a mixture by heating a liquid to a
suitable temperature until it forms vapour (gas) and then cooling it back to liquid.
In distillation process cooling process is done in the lie big condenser. The liquid formed after cooling the vapour is called distillate.
TYPES OF DISTILLATION
There are two types of distillation (i) Simple distillation (ii) Fractional distillation
(i) Simple distillation
Definition: Simple distillation is the process of obtaining single liquid from a suspension or a solution by boiling the mixture to form vapour and then condensing vapour back a liquid.
Diagram to show separation of water and muddy by simple distillation
Simple Distillation can be used to separate
(i) Distilling water from muddy water (ii) Distilling water from salt water
NB: Simple distillation is used to purify water which is used in schools, hospitals, industries etc.
QUESTIONS
- What role does the liebig condenser play?
2. If you do not have a liebig condenser, what will you use to carry out this simple distillation?
(ii) Fractional distillation
Definition: Fractional distillation is a method of separating homogeneous mixture of two or more liquids which have different boiling points by means of a fractionating column.
A mixture of water and ethanol is a good example in which ethanol boils at 78oC and water boils at 100oC. Ethanol boils. at 78oC and is distilled first leaving behind water which will boil at 100oC.
Diagram to show separation of ethanol and water by fractional distillation
The fractionating column separates the two liquids, the one with a lower boiling point moves to the upper part of the column and distils over. The liquid with the lower boiling point is collected first as a distillate. Each component collected is known as a fraction.
Fraction Distillation can be used
(i) Separation and purification of ethanol from mixture of ethanol and water
(ii) Separation of petroleum into its fractions (components) such as petro, diesel, kerosene
NB: In fractional distillation
(i) The liquids with lower boiling point is first collected as distillate
(ii) Each component collected is called fraction
Application of Distillation (Generally distillation is used in)
(i) Purification of water
(ii) Manufacture of alcohol
(iii) Separation of components of crude oil (petroleum) Eg petrol, diesel
5. LAYER SEPARATION
Definition: Layer separation is the process of separating immiscible liquids using a separating funnel
Immiscible liquids are liquids which do not mix up and form distinct layers when put together. Liquid with high density settles at the bottom while the liquid with low density remains at the top of the separating funnel.
Example of mixtures which can be separated by layer separation are
(i) Kerosene and water (ii) Cooking oil and water
Diagram to show separation of mixtures by layer separation method (eg separation of water and kerosene)
Water and kerosene
Separation Application of Layer separation
Recovery of liquids from contaminations
6. SUBLIMATION
MEANING: Sublimation is a process by which solid changes directly to gas on heating without passing into liquid state.
Diagram to show separation of iodine and sand
NB: (i) Solid that forms after the vapour cools is called sublimate
(ii) This method is used to separate mixture where one component sublimes
(iii) Iodine and ammonium chloride are few compounds can sublime
(iv) The reverse process of change from vapour to solid on cooling is called Deposition
Sublimation can be used to
(i) Separate iodine from mixture of sand and iodine
(ii)Separate ammonium chloride from mixture of salt and ammonium chloride
Separation Application of Sublimation is in Purification of substance.
7. CHROMATOGRAPHY
Definition: Chromatography is the process of separating mixtures using a moving solvent on a material
that absorbs the solvent.
It is a method which is used to separate coloured mixtures.
In chromatography a mixture is firstly dissolved in a fluid called mobile phase. This fluid carries the mixture through a stationary phase.
- The moving solvent is called mobile phase and may be a gas or liquid
- The mobile phase flows through the stationary phase and caries the components of the mixture with it
- The immobile substance is called stationary phase and is a material that absorbs solvent which can be either solid or liquid supported on a solid.
- Substance separated is called Analyte
TYPES OF CHROMATOGRAPHY
There are three types
(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
Uses of chromatography
Chromatography is used in
(i) Medicine (ii) Security (iii) Chemistry (iv) In industries (v) In biology (vi) In health
In medicine
Used as follows
(i) Used in Studying blood cells (ii) Used in detecting types of drugs in blood
In security
Used as follows
(i) Used to analyses blood in crime scenes (ii) Used in detecting different fibres
(iii) Used in drug testing.
In chemistry
Used as follows
(i) Used in test purity or composition of organic substances (ii) Used in separates mixture
In industries
(i) Used in testing quality of products
(ii) Used in purification of substances
(iii) Used in testing shelf-life of food substances
In biology
Use as follows
(i) Used in protein analysis
(ii) Used in plasma analysis
(iii) Used in enzyme analysis
Health and environment
Used as follows
(i) Used in testing for water pollution, soil pollution and air pollution
(ii) Used in testing for food contamination
8. SOLVENT EXTRACTION
MEANING: Solvent extraction is a process of separating component of a mixture using a solvent that
dissolves selected component
OR Solvent extraction is a method of separating one substance from one or more other
substances by using a solvent.
For example, extracting essential oils from plant seeds using a liquid that dissolves the oils.
NB: In solvent extraction, the following conditions should be considered when choosing a solvent.
(i) The chosen solvent should dissolve the component of interest
(ii) The solvent must not react with the component of interest
(iii) The solvent chosen should be easily separated from component of interest
(iv) It must not be toxic or corrosive
Separation Application of Solvent
(i) It is used to extract cooking oil from seeds or nuts eg oil from ground nuts, coconuts,
cotton seeds, sunflower etc
(ii) It is used to extract tea component from tea leaves using hot water during preparation
of tea.
9. MAGNETIZATION (MAGNETIC SEPARATION)
Meaning: 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. Eg a mixture of iron and sand, iron and sulphur etc
Diagram to show separation of iron and sand and salt (common salt)
10. Winnowing
Definition: Winnowing is a method used to separate a mixture of two or more solids with different densities.
This is mostly applied in purifying different grains to remove the unwanted materials.
Examples: (i) Maize and husks (ii) 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. Eg a sieve for maize flour
11. CENTRIFUGATION
A centrifuge is used to separate small amounts of suspension. Centrifugation is used with insoluble solids where the particles are very small and spread throughout the liquid. In centrifugation, test tubes containing suspensions are spun round very fast. The solid gets thrown to the bottom. Here, a huge centrifugal force acting on the particles due to the high speed spinning of the samples makes the particles to settle at the bottom
12. 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.
Defn. (1) Crystallization is a process of forming crystals from a super saturated solution when left to cool
(2) Crystallization point is a point at which crystals form.
Crystallization is used in sugar and salt industry to obtain sugar and salt crystals.
Eg 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 basins
13. HAND PICKING
Meaning: 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
REVISION QUESTIONS
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
(v Water and ethanol (vi) Iron and mud (vii) Water and flour (viii) Water and mud
(ix) Rice grains and husks
2. (a) In a tabular form, state 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:
(i) The heating of a salt solution (ii) The action of heat on ice
(iii) The burning of paper or wood in air (iv) The rusting of iron in air
(v) Fermentation of milk
(vi) The melting of a metal
4. Differentiate between a homogenous mixture and a heterogeneous mixture.
3. Write TRUE for statements that are correct and FALSE for statements that are not correct.
(i) Matter exists in three states namely, solid, liquid and gas. _________
(ii) A liquid has no fixed volume. ______________
(iii) A change in state from gas to solid is called sublimation. _________
(iv) In a physical change, a new substance is usually formed. __________
(v) Metals are shine and can be polished. ________
(vi) The components of a compound can be separated by physical means only. _______
(vii) The liquid state is one in which the particles are moving freely in all directions. ______
(viii) Condensation is the same as solidification. __________
(ix) Boiling occurs at one particular temperature. _____________
(x) Iodine sublimes when heated. ___________
4. (a) In the following diagram label letters P, Q and Z
(b) What is the name of the process of separating mixtures is represented by the diagram?
