Material and Separation of Substances

All objects around us are made of one or more materials. These materials may be glass, metal, plastics, wood, cotton, paper, mud or soil. 

Objects around us are made up of a large variety of materials. A given material could be used to make a large number of objects. It is also possible that an object could be made of a single material or of many different types of materials.

Different types of materials have different properties.

Properties Of Material: 

We choose a material to make an object depending on its properties, and the purpose for which the object is to be used.

Appearance:

Materials that have such lustre are usually metals. Iron, copper, aluminium and gold are examples of metals. Some metals often lose their shine and appear dull, because of the action of air and moisture on them.

Hardness: 

Materials which can be compressed or scratched easily are called soft while some other materials which are difficult to compress are called hard. For example, cotton or sponge is soft while iron is hard.

Soluble or Insoluble:

• Those substances which get completely disappeared or dissolved in water, are said to be soluble in water.
• Other substances do not mix with water and do not disappear even after we stir for a long time. These substances are insoluble in water.
• Water plays an important role in the functioning of our body because it can dissolve a large number of substances.
• Some liquids get completely mixed with water. Some others do not mix with water and form a separate layer when kept aside for some time.
• Some gases are soluble in water whereas others are not. oxygen gas dissolved in water is very important for the survival of animals and plants that live in water.

Transparency: 

• Those substances or materials, through which things can be seen, are called transparent. Glass, water, air and some plastics are examples of transparent materials.
• On the other hand, there are some materials through which you are not able to see. These materials are called opaque.Wood, cardboard and metals, are examples of 
  opaque  materials. 
• The materials through which objects can be seen, but not clearly, are known as translucent.

Method of Separation:

Handpicking, winnowing, sieving, sedimentation, decantation and filtration are some of the methods of separating substances from their mixtures.

1. Hand Picking:

The method of handpicking can be used for separating slightly larger sized impurities like the pieces of dirt, stone, and husk from wheat, rice or pulses. The quantity of such impurities is  usually not very large.

2. Threshing:

The process that is used to separate grain from stalks etc. is threshing. In this process, the stalks are beaten to free the grain seeds.

Sometimes, threshing is done with the help of bullocks. Machines are also used to thresh large quantities of grain.

3. Winnowing:

Winnowing is used to separate heavier and lighter components of a mixture by wind or by blowing air.

This method is commonly used by farmers to separate lighter husk particles from heavier seeds of grain. The separated husk is used for many purposes such as fodder for cattle.

4. Sieving:

Sieving is used when components of a mixture have different sizes.

5. Sedimentation, Decantation and Filtration:

When the heavier component in a mixture settles after water is added to it, the process is called sedimentation. When the water (along with the dust) is removed, the process is called decantation.

The same principle is used for separating a mixture of two liquids that do not mix with each other.

Pouring the tea through a strainer is an example of filtration. Fruit and vegetable juices are usually filtered before drinking to separate the seeds and solid particles of pulp. The method of filtration is also used in the process of preparing cottage cheese (paneer) in our homes.

6. Evaporation:

The process of conversion of water into its vapour is called evaporation. The process of evaporation takes place continuously wherever water is present.

we can use the process of evaporation, to separate a mixture of water and salt.

Where do you think, salt comes from?

Sea water contains many salts mixed in it. One of these salts is the common salt. When sea water is allowed to stand in shallow pits, water gets heated by sunlight and slowly turns into water vapour, through evaporation. In a few days, the water evaporates completely leaving behind the solid salts. Common salt is then obtained from this mixture of salts by further purification.

Notes:

• The process of conversion of water vapour into its liquid form is called condensation.
• Difference in the size of particles in a mixture is utilised to separate them by the process of sieving and filtration.
• Filtration can be used to separate components of a mixture of an insoluble solid and a liquid.

Solution and Saturation of solution:

A solution is prepared by dissolving a substance in a liquid. A solution is said to be saturated if it cannot dissolve more of the substance in it.

More of a substance can be dissolved in a solution by heating it. Water dissolves different amount of soluble substances in it.

Changes around us:

Many changes are taking place around us on their own. In the fields, the crops change from time to time. Sometimes, leaves fall from trees, change colour and dry out. The flowers bloom and then wither away. Our nails grow, our hair grows, we grow taller and our weight increases as we grow. These all are examples of changes which keep happening around us.

Some changes can be reversed and some cannot be reversed. 

A change may occur by heating a substance or by mixing it with some other.

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