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