Detailed Classification of Materials with Examples

The study of acids and bases is an essential part of Chemistry Topics, as it examines their properties and reactions.

what is the basis of classification of materials?

The materials are classified on the basis of certain properties such as :

1. Appearance (Shiny or Dull)
2. Hardness or Softness
3. Solubility or Insolubility in water
4. Heaviness or Lightness with respect to water
5. Transparency, Translucency or Opaqueness

We will now discuss all these different methods for the classification of materials in detail, one by one.

1. Classification of Materials on the Basis of Their Appearance

If we look at a gold ornament, we find that it has a shiny appearance. In science, the shiny appearance is indicated by the term ‘lustre’. So, gold is said to have lustre (chamak). On the other hand, if we look at a piece of wood, it does not have a shiny appearance. Wood does not have lustre (chamak). Wood has a dull appearance. Thus, some materials have a shiny appearance whereas other materials do not have a shiny appearance. So, on the basis of their appearance, all the materials are classified into two groups :

1. Materials having lustre (or shiny appearance), and
2. Materials having no lustre (or dull appearance).

Those materials which have shiny appearance are said to have lustre. All the metals like gold, silver, copper, aluminium, and iron, etc., are the materials having shiny appearance (or lustre). Some metals (like iron, copper, and aluminium, etc.) often lose their shine and appear dull due to the action of air and moisture on their surface. So, we should look for lustre only on the freshly cut surface of such metals or after rubbing their surface with a sand paper. The examples of materials having lustre or shine are :

Metals (such as Gold, Silver, Copper, Aluminium and Iron), Metal alloys (such as Steel, Stainless steel, Brass, etc.) and Diamond. All the objects made of metals, their alloys and diamonds also have shiny appearance or lustre. For example, a steel spoon has lustre or shiny appearance. The objects made of cut-glass also have lustre or shiny appearance. Even a glass bowl has shine on its surface.

Those materials which have dull appearance are said to have no lustre (no shine). The examples of materials having dull appearance (without lustre or shine) are : Paper, Cardboard, Wood, Chalk, Cotton, Plastic, Rubber, and Sand. All the objects made from these materials will also have dull appearance.

We will now answer one question based on the appearance of materials.

Example Problem.
Find the odd one out from the following : Aluminium, Iron, Copper, Silver, Sand
Answer:
Aluminium, iron, copper and silver are all metals having a shiny appearance or lustre. On the other hand, sand is a material which has dull appearance having no shine or lustre. So, the odd one is sand.

2. Classification of Materials on the Basis of Hardness and Softness

If we press a piece of iron metal with our hands, we will find that it cannot be compressed at all. A piece of iron can also not be cut, bent or scratched easily. We say that iron is a hard material. In other words, iron has the property of hardness. On the other hand, if we press a piece of sponge between our hands, we will find that it can be compressed easily into a smaller size. A piece of sponge can also be cut, bent or scratched easily. We say that sponge is a soft material. In other words, sponge has the property of softness.
All the materials can be divided into two groups on the basis of their hardness or softness :

1. Hard materials, and
2. Soft materials.

Those materials which cannot be easily compressed, cut, bent (moulded) or scratched, are called hard materials. Some of the examples of hard materials are : Iron, Steel, Wood, Stone, Brick, Glass, Bones, Teeth, and Diamond. Diamond is the hardest natural material known.

Those materials which can be easily compressed, cut, bent (moulded), or scratched, are called soft materials. Some of the examples of soft materials are : Sponge, Cotton, Wool, Foam rubber, Candle wax, Butter, Chalk, Clay, Flour, Feathers, Skin and Tomato.

3. Classification of Materials on the Basis of Their Solubility in Water

Water dissolves a large number of materials but it cannot dissolve all the materials. Thus, some materials are soluble in water whereas other materials are insoluble in water. So, all the materials can be classified into two groups on the basis of their solubility:

1. Materials which are soluble in water, and
2. Materials which are insoluble in water.

We will understand this classification more clearly by performing some activities.

Activity 1
We take a test-tube and fill it half with water. Add half a spoon of sugar in it [see Figure (a)]. Shake the test-tube well and observe it. We will find that the sugar has disappeared into water [see Figure (b)]. We say that the sugar has dissolved in water or that the sugar is soluble in water. Please note that the sugar is still there in water but its particles have become so small and spread so uniformly in water that we cannot see them. From this

activity we conclude that sugar is a material which is soluble in water. Some more materials which are soluble in water are : Common salt, Washing soda, Potassium permanganate, Copper sulphate (Blue vitriol), Alum, Milk, Lemon juice, Glycerine and Alcohol. Water (or any other liquid) containing a dissolved material in it is called a solution. For example, water having sugar dissolved in it is called sugar solution, Water plays an important role in the functioning of our body beause it can dissolve a large number of substances.

We now take another test-tube and fill it half with water. Add half a spoon of sand in [see Figure (a)]. Shake the test-tube well and observe it. We will find that the sand settles down at the bottom of the test-tube Isee Figure (b)]. Sand does not dissolve in water. From this

activity we conclude that sand is a material which is insoluble in water. Some more materials which are insoluble in water are: Chalk powder, Saw-dust, Sulphur, Glass, Plastic, Paper, Flour, Wax, Mustard oil, Groundnut oil, Coconut oil, Kerosene, and Petrol.

Activity 2
We will now discuss the solubility of some liquid materials in water. Glycerine is a liquid material. We take a test-tube and fill it half with water. Add some glycerine to it. Shake the test-tube well. Allow it to stand for some time and observe. We will see that glycerine has completely mixed with water to form a single layer. We say that glycerine has dissolved in water or that glycerine is soluble in water. Please note that to tell that a liquid is soluble in water, we can also say that the liquid is miscible with water. So, in this case we can say that glycerine is miscible with water. Some more liquid materials which are soluble in water or miscible with water are : Milk, Lemon juice, Vinegar and Alcohol.

Mustard oil is also a liquid material. It is an edible oil (which can be used for cooking food). We take a test-tube and fill it half with water. Add some mustard oil to it. Shake the test-tube well. Allow it to stand for a few minutes and observe. We will see two separate layers of water and mustard oil in the test-tube. Water being heavier, forms the lower layer in the test-tube whereas mustard oil being lighter, forms the upper layer in the test-tube.

This shows that mustard oil does not mix up with water. We say that mustard oil is insoluble in water or mustard oil is immiscible with water. Groundnut oil, coconut oil, kerosene and petrol are some other liquid materials which are insoluble in water or immiscible with water. Please note that those liquids which do not mix with water can, however, mix among themselves. For example, groundnut oil can mix with coconut oil to form a single layer. Similarly, kerosene can mix with petrol to form a single layer.

We will now discuss the solubility of gases in water. Some gases dissolve in water whereas other
gases do not dissolve in water. In other words, some gases are soluble in water whereas other gases are insoluble in water. Oxygen gas dissolves in water. That is, oxygen gas is soluble in water. The plants and animals which live in water use the oxygen dissolved in water for respiration.

Thus, oxygen gas dissolved in water is very important for the survival of animals and plants that live in water. Carbon dioxide gas also dissolves in water. That is, carbon dioxide gas is also soluble in water. The plants which live in water use the carbon dioxide dissolved in water for the process of photosynthesis. There are, however, some gases which do not dissolve in water. The two examples of gases which do not dissolve in water breathing.
(or which are insoluble in water) are : nitrogen and methane (or marsh gas). Let us answer some questions now.

Example Problem 1.
Classify the following materials on the basis of their solubility or insolubility in water :
Milk, Flour, Washing soda, Copper sulphate, Chalk powder, Common salt, Sugar, Sand, Wax, Alcohol, Alum, Glass, Plastic, Kerosene, Potassium permanganate and Coconut oil
Answer:
We can classify all these materials into two groups on the basis of their solubility in water as follows:
Materials soluble in water : Materials insoluble In water
Milk : Flour
Washing soda : Chalk powder
Copper sulphate : Sand
Common salt : Wax
Sugar : Glass
Alcohol : Plastic
Alum : Kerosene
Potassium permanganate : Coconut oil

Example Problem 2.
Find the odd one out from the following :
Sugar, Salt, Sand, Copper sulphate
Answer:
Sugar, salt and copper sulphate are soluble in water but sand is insoluble in water. So, the odd one is sand.

4. Classification of Materials on the Basis of Their Heaviness or Lightness With Respect to Water

Some materials are heavier than water whereas other materials are lighter than water. In science, the heaviness or lightness of a material is indicated by the term ‘density’. A substance which is heavier than water is said to have higher density than water whereas a substance which is lighter than water is said to have lower density than water.

All the materials can be classified into two groups on the basis of their density:

1. Materials which are heavier than water, and
2. Materials which are lighter than water.

In order to find out whether a material is heavier than water or lighter than water, we put a piece of the material in a vessel containing water:

1. The material which sinks in water is heavier than water.
2. The material which floats on water is lighter than water.

Activity 3
We take a beaker and fill it about two-thirds with water. Let us drop an iron nail in this water. We will find that the iron nail sinks in water and settles down at the bottom of the beaker [see Figure (a)], This activity shows that iron is a material which is heavier than water. Some of the materials which are heavier than water are : Iron, Aluminium, Copper, Silver, Gold, Stone, Glass, Chalk and Soil. All the materials which are heavier than water, sink in water.

Let us now take another beaker and fill it about two-thirds with water. Drop a small piece of wood in this water. We will find that the piece of wood starts floating on water [see Figure 14(6)]. It does not sink in water. This activity shows that wood is a material which is lighter than water. Some of the examples of materials which are lighter than water are : Wood, Plastic, Saw-dust, Dry leaves, Ice, Oil (Groundnut oil, Mustard oil, Coconut oil, etc.), Kerosene and Petrol. All the materials which are lighter than water, float on water.

5. Classification of Materials on the Basis of Transparency, Translucency and Opaqueness

The property of a material due to which we can see through it clearly is called transparency ; the property of a material due to which we cannot see through it clearly is called translucency ; and the property of a material due to which we cannot see through it at all is called opaqueness.
All the materials can be divided into three groups on the basis of transparency, translucency and opaqueness :

1. Transparent materials,
2. Translucent materials, and
3. Opaque materials.

We will now discuss these three types of materials, one by one. Let us start with transparent materials.

Those materials through which we can see clearly are called transparent materials. For example, we can see clearly through a glass window, so glass is a transparent material. The transparent materials allow almost all the light to pass through them due to which the objects behind them can be seen clearly. Some of the examples of transparent materials are : Glass, Air, Water, Some plastics (like Polythene), Groundnut oil, Alcohol, etc. Transparent materials are called ‘pardarshi’ in Hindi.

We can see clearly through transparent materials. For example, if we look at a burning candle through a sheet of clear glass, we can see the candle and its flame clearly. This is because the transparent glass sheet allows all the light coming from the candle and its flame to pass through it and reach our eyes. The window-panes in our homes are usually made of transparent glass.

Our spectacle glasses are also transparent. The glass tumbler in our kitchen is also a transparent object. The test-tubes, beakers and flasks in the science laboratory are all transparent objects. The shopkeepers usually keep the sweets, biscuits, toffees and chocolates, etc., in transparent containers made of glass or plastic so that customers can see these items easily. If we look at a swimming pool filled with clean water, we can see its bottom clearly through water. This shows that water is a transparent material. We are all surrounded by air around us. Since we can see the things around us through air, so air is also a transparent material.

Those materials through which we cannot see clearly are called translucent materials. For example, we cannot see clearly through the ground glass window of our bathroom, so ground glass is a translucent material. Translucent means semi-transparent. The translucent materials allow only a small amount of light to pass through them due to which the objects behind them cannot be seen clearly. Some of the examples of translucent materials are : Ground glass, Butter paper (Tracing paper), Oiled paper, Tissue paper, Muddy water and Clouds. Translucent materials are called ‘ardhapardarshi’ in Hindi.

We cannot see clearly through a translucent material. For example, if we look at a burning candle through a piece of ground glass (or butter paper), we can see only a dim light of the candle. We can neither see the candle itself nor the candle flame clearly through the ground glass (or butter paper) which are translucent materials. The windows of bathrooms in our homes are made of translucent material called ground glass so that though some outside light may enter the bathroom but nothing is visible clearly from outside.

Activity 4
We can make a translucent material ourselves as follows:
Take a sheet of paper and look through it at a burning candle. We will not be able to see much candle light through this sheet of paper. Now, put 5 to 6 drops of coconut oil at its centre.

Spread and rub the oil on the paper with your fingers. This gives us an oiled paper. Let us now look at the burning candle through that part of paper on which oil has been rubbed. We will find that more light of the burning candle can be seen through the oiled paper (which is a translucent material). Please note that though we can see more candle light coming through the oiled paper but we cannot see the candle flame clearly.

Those materials through which we cannot see at all, are called opaque materials. For example, we cannot see through a sheet of cardboard, so cardboard is an opaque material. The opaque materials do not allow any light to pass through them due to which the objects kept behind them cannot be seen at all. Some of the examples of opaque materials are : Cardboard, Wood, Metals, Brick, Stone, and Book, etc. An opaque material is called ‘apardarshi’ in Hindi.

We cannot see anything through an opaque material. For example, if we look at a burning candle through a piece of cardboard held in front of our eyes, we cannot see anything at all. This is because cardboard (being opaque) does not allow the light of candle flame to pass through it and reach our eyes. We cannot tell what is kept in a wooden box, a cardboard carton or a metal container because all these objects are made of opaque materials. We can also not see behind a wall because it is made of opaque material called bricks.

Activity 5
Let us now find out whether the palm of our hand is transparent, translucent or opaque. This can be done as follows : Take a torch and cover its glass with the palm of your hand in a dark room. Switch on the light of the torch and observe the other side of the palm. We can see some faint, red light through our palm. Since the palm allows some light to pass through it, so it is a translucent material.