Pure substances are those substances that are made up of only one kind of particles. More precisely, they are composed of only one type of atoms or molecules.
There are two types of pure substances:-
Element: They consist of linking one or more same atoms. For example, hydrogen atoms, oxygen atoms and iron, etc.
Compound: When different atoms or molecules are linked together, then they form a compound. For example, carbon dioxide, sodium chloride and water, etc.
When unwanted components are added to the food items then they are called adulteration, like small stones in rice(Figure 1).
Figure 1: Separation of small pieces of stones from rice.
The formation of any substance by mixing one or more substances is called a mixture. Moreover, the mixed substances possess unique property. Some examples are
Milk is composed of a mixture of water and cream
Water, carbon dioxide and sugar are mixed to form an aerated drink
The mixture of water, dead organic matter and broken rocks, and minerals create soil
The mixture contains different substances called its components that can be present in ratios.
Properties of Mixtures
The components ratio in a mixture cannot be fixed.
The components can be separated by simple methods of separation. For example, separating stones from rice by hand.
The melting and boiling point of mixtures is not fixed.
Types of Mixtures
There are two types of mixtures:-
i. Homogeneous mixture: In a mixture, the components are evenly distributed. Some examples of homogeneous mixture are the dissolution of salt in the water, alloys(made up of copper steel and bronze), and pure air
ii. Heterogeneous mixture: These mixtures do not have evenly distributed components. Some examples are fruit salad and chocolate chip cookies, etc(Figure 4).
Figure 4: Heterogeneous mixture of dry fruits.
SEPARATION OF SUBSTANCES FROM MIXTURES
The following purposes for separating components from mixtures are:-
To remove impurities or harmful components: The impurities affect health. Therefore, they need to be removed. For example, purifying river water for drinking, removing stones and other impurities from rice and pulses.
To obtain useful components: The distillation of petroleum to obtain useful components like petrol, kerosene, diesel and white petroleum jelly.
To obtain pure components: The separation of pure metals from their natural forms is called ores.
METHODS OF SEPARATION
Separation is a method of separating one substance from a mixture of two or more substances.
Separation of Solids from Other Solids
Separation solids from the mixture of solids can be performed by the following methods:-
It is a method of separation by using hands. The following purposes where handpicking is applicable are:-
i. When components are visible to the naked eye.
ii. The shape, size and colour of the components are different from the useful materials.
iii. The size of the components is large.
Some examples of handpicking methods are small stones, broken grains are separated from rice, wheat and pulses.
The process of separating grains from the harvested stalk is called threshing. It can be performed by the following ways(Figure 6):-
i. Beating the dry stalks on the hard surface by hands.
ii. Threshing machines are also used to separate dried grains.
iii. Crushing the stalks by animals like bullocks.
For example, threshing is used to separate the grains from the stalks of harvested rice and wheat crops.
Figure 6: Threshing process.
The process of separating grains from the husk is called winnowing. In this method, the mixture of grains and husk drops from a height, then the wind carried the husk away from the grains, as grains are heavier than the husk, they form a heap near the performer. Some examples of winnowing method are separation of sand from the powdered dry leaves(Figure 7).
Figure 7: Winnowing method.
The process of separating the components according to their size is called sieving. A sieve is composed of a net or mesh. The size of the pores on the net or mesh depends on the size of the wanted materials(Figure 8).
The most common example of sieving method is the separation of bran from the wheat flour.
Figure 8: Sieving method.
5. Magnetic Separation:
The process of separating magnetic properties possessing materials from substances is called magnetic separation. In a mixture, one component is attracted to the magnet while the other one is not. For example, the separation of iron from the sand by a magnet(Figure 9).
Figure 9: Magnetic separation method.
Separation of Solids from Liquids
In this separation, the method is dependent on the solubility of the substance. Separating insoluble solids from liquids
Such particles that are not soluble in the water can be separated by the following methods:-
1. Sedimentation and Decantation:
Sedimentation is the process of separating insoluble materials from liquid. The insoluble components settle down at the bottom of the liquid forms sediment, and the liquid above the sediment is called supernatant.
Afterwards, the supernatant is carefully removed out of the container without disturbing the sediment is called decantation. For example, separation of fine particles from the muddy water can be done by this method(Figure 10).
Figure 10: Sedimentation and decantation method:
The separation of insoluble components from the mixture using a filter is called filtration. The fine particles that are stored on the filter paper or funnel are called a residue, while the pure liquid that passes through the funnel into a container is called the filtrate(Figure 11).
Figure 11: Filtration.
Separating soluble from their solutions
The separation of soluble solids from the mixture as follows:-
1. Evaporation: The process of separating the soluble materials from the solution by heating it is called evaporation. For example, the formation of the common salt from the seawater by evaporation occurs naturally(Figure 12).
2. Condensation: The process of converting the water vapours into the water by cooling is called condensation. Raining is a good example of this process(Figure 12).
Figure 12: Evaporation and Condensation. Also Read