Classification of Materials

Question 1 What is the importance of oxygen gas dissolved in water? How is the carbon dioxide gas dissolved in water helpful to the plants which live in water?

Question 2 What is meant by hard material and soft materials? Give examples?

Question 3 What is meant by transparent material? Give 2 example?

Question 4 What is meant by translucent material? Give 2 example?

Question 5 What is meant by opaque material? Give example?

Question 6 Name 2 material which are heavier than water and two which are lighter than water?

Question 7 Name 2 materials which float on water and two which sink in water?

Question 8 Name two materials which are soluble in water?

Question 9 Name two materials which are insoluble in water?

Question 10 How will you show that steel and sponge differ from each other?

Question 11 How will you classify the materials on the basis  of properties?

Question 12 Define the word lusture? Give few examples of material having shiny lusture and dull appearance?

Question 13 What are hard and soft materials?

Question 14 Give an activity to show that wood floats on water?

Also Read NCERT Solutions for Chapter 4 Sorting Materials into Groups

 

Classification of materials

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

(1) Appearance

(2) Hardness or softness

(3) Solubility and insolubility in water

(4) Heaviness or lightness with respect to water

(5) Transparency, translucency or opaqueness

Classification of material on the basis of their appearance

On the basis of their appearance, all the materials are classified into two groups:

(1) Materials having lustre or Shiny appearance

(2) Material having no lustre or dull appearance

Those materials which have shiny appearance are said to have lustre.

For example: Metals like gold, silver, copper, aluminium, iron are the materials having shiny appearance

Some metals like iron, copper, aluminium often lose their shine and appear dull due to the action of air and moisture on their surface. We should look for lustre only on the freshly cut surface of such metals or after rubbing their surface with a sand paper.

Examples of material having lustre or shine are metals such as gold, silver, copper, aluminium and iron, metal alloys such as steel, stainless steel, brass and diamond.

Those materials which have dull appearance are said to have no lustre.

For example: paper, wood, chalk, cotton, plastic, rubber, cardboard etc.

 

Classification of material on the basis of hardness and softness

If we press a piece of iron nail with our hands, we will find that it cannot be compressed at all. A piece of iron cannot be cut, bend or scratched easily. Iron is a hard material.

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. Sponge is a soft materials.

All the materials can be divided into two groups on the basis of their hardness or softness:

(1) Hard materials

(2) Soft material

Those materials which cannot be easily compressed cut, moulded or scratched are called hard materials.

For example: Iron, steel, wood, stone, brick, glass, bone, teeth, diamond.

Those materials which can be easily compressed cut, moulded or scratched are called soft material.

For example: Sponge, cotton, wool, foam, rubber, candle wax, butter, chalk, clay, feathers, flour, skin etc.

Classification of materials on the basis of their solubility in water

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

(1) Materials which are soluble in water

(2) Materials which are insoluble in water

Activity 1

(1) Take a test tube and fill it half with water.

(2) Add half a spoon of sugar in it.

(3) Shake the test tube well and observe it.

(4) We will find that the sugar has disappeared in water or that the sugar soluble in water.

Sugar is a material which is soluble in water.

Some materials which are soluble in water are common salt, sugar, washing soda, potassium permanganate, copper sulphate, alum, milk, lemon juice, alcohol, glycerine etc.

Water containing a dissolved material in it is called sugar solution.

Water having sugar dissolved in it is called sugar solution.

Activity 2

(1) Take another test tube and fill it half with water.

(2) Add half a spoon of sand in it.

(3) Shake the test tube well and observe it.

(4) We will find that the sand settles down at the bottom of the test tube.

(5 ) Sand does not dissolve in water.

Sand is a material which is insoluble in water.

Materials which are insoluble in water are chalk powder, saw-dust, sulphur, glass, plastic, paper, floor, wax, mustard oil, groundnut oil, coconut oil, kerosene and petrol.

Activity 3

(1) Take a test tube and  fill it half with water. Add some glycerine to it.

(2) Shake the test-tube well.

(3) Allow it to stand for sometime and observe.

(4) Glycerine has completely mixed with water to form a single layer.

(5) Glycerine has dissolved in water or that glycerine is soluble in water or glycerine is miscible with water.

Materials which are soluble in water are use vinegar, alcohol, milk, lemon juice.

Activity 4

(1) Mustard oil is also a liquid.

(2) We take a test tube and fill it half with water. Add some mustard oil to it.

(3) Shake the test tube well. Allow it to show it to stand for few minutes and observe.

(4) 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.

(5) This shows that mustard oil does not mix up with water.

(6) Mustard oil is insoluble in water or mustard oil is immiscible with water.

Some other liquid material which are insoluble in water are groundnut oil, coconut oil, kerosene, petrol etc.

Some gases are soluble in water whereas other gases are insoluble in water. Oxygen gas dissolved in water. The plants and animals which live in water use the oxygen dissolved in water for respiration. Oxygen gas dissolved in water is very important for the survival of animals and plants that live in water.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. The gases which do not dissolve in water are nitrogen and methane.

Classification of material 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.

A substance which is heavier than water is said to have higher density than water where as 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

(2) Materials which are lighter than water

Activity

(1) We take a beaker and fill it about 2/3rd with water.

(2) let us drop an iron nail in this water. We will find that iron nail sinks in water and settles down at the bottom of the beaker.

(3) This shows that iron is a material which is heavier than water.

Materials which are heavier than water are iron, aluminium, copper, silver, gold, stone, glass, chalk, soil

All the materials which are heavier than water, sink in water.

Activity

(1) Take another beaker and fill it about two-third with water.

(2) Drop a small piece of wood in this water. The piece of wood starts floating on water.It does not sink in water. The piece of wood is a material which is lighter than water.

Examples of material which are lighter than water are wood, plastic, dry leaves, ice, oil, kerosene, petrol .

Materials which are lighter than water float on water.

Classification of material 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 .

Those material through which we can see clearly are called transparent material.

Transparent materials allow almost all the light to pass through them due to which the objects behind them can be seen clearly.

For example:  glass, air, polythene, groundnut oil, alcohol.

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 glass tumbler, test tube, beaker are transparent. Shopkeeper keep the sweets, biscuits toffees and chocolates in transparent containers made of glass or plastic so that customer can see these items easily.

The property of material due to which we cannot see through it clearly is called translucency.

Those material through which we cannot see clearly are called translucent material.

Translucent means semi-transparent.

Translucent materials allow only a small amount of light to pass through them due to which the object behind them cannot be seen clearly.

For example: Oiled paper, tissue paper, muddy water, clouds etc.

If we look at a burning candle through a piece of ground glass, we can see only a dim light of the candle. We can neither see the candle itself not the candle flame clearly through ground glass which are translucent materials.

The windows of bathroom in our homes are made of translucent material so that though some outside light may enter the bathroom but nothing is visible clearly from outside.

The property of material due to which we cannot see through it at all is called opaqueness.

Those material through which we cannot see at all, are called opaque material.

For example: cardboard, wood, bricks, metal, book etc.

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 does not allow the light of candle flame to pass through it and reach our eyes.

 

Other notes from Chapter 4 Classification of Objects Classification of Objects Materials Classification of Material