Sorting materials into group (part -4) class 6


Sorting materials into group

Q.14. How can we classify materials on the basis of hardness or softness?
Ans.14. Materials which are difficult to get compressed, cut, bent (moulded)  or scratched are called hard materials. For example: Iron, Steel, Wood, Stone, Brick, Glass, Bones, Teeth, Diamond etc.

Materials which can be compressed, cut, bent (moulded) or scratched easily are called soft materials. For example: Sponge, cotton, wool, Foam rubber, candle wax, butter, chalk, clay, flour, feathers, skin, tomato etc.

Q.15. How can we classify materials on the basis of their solubility in water?
Ans.15. Those substances which get mixed with water and disappear are said to be soluble in water. For example: Vinegar, Milk, lemon juice, alcohol, common salt, copper sulphate, baking powder, sugar etc.

Those substances which do not mix with water and do not disappear even after we stir for a long time. These substances are insoluble in water. For example: Chalk powder, glass, plastic, oil, flour, saw dust, sand, wax etc. 

Q.16. What is the importance of solubility of oxygen and carbon dioxide gases in water?
Ans.16. The importance of solubility of oxygen and carbon dioxide gases in water is as follows:
  • Oxygen gas is soluble in water. The plants and animals which live in water use the oxygen dissolved in water for respiration.
  • 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.  
Q.17. Name two gases which are insoluble in water?
Ans.17.  Examples of gases which do not dissolve in water (or which are insoluble in water) are: nitrogen and methane. 

Q.18. Why do some materials float while other sink in water?
Ans.18. Density means mass per unit volume. Materials float or sink in water due to the difference in densities with respect to water.

 The materials which have higher density than water (heavier than water), they sink in water. For example: Iron, aluminium, copper, silver, gold, stone, glass, chalk, soil etc.

The materials which have lower density than water (lighter than water), they float on water. For example: Ice, wood, plastic, sponges, balloons, oil, thermocol, wax etc.
Q.19. How can we classify materials on the basis of their transparency?
Ans.19. On the basis of their transparency, the materials can be classified as transparent, translucent and opaque materials.
Transparent materials
•   Those substances or materials, through which things can be seen clearly, are called transparent.
•      Light can pass through them easily.

•      For example: Clear glass, clean water, some plastics, air etc.

Translucent materials
•    Those substances or materials, through which things can not be seen clearly but partially, are called translucent.
•      Light can pass through them partially.
•      For example: Ground glass, clouds, butter paper, oiled paper, some plastics etc.

Opaque materials
•      Those substances or materials, through which things can not be seen at all, are called Opaque.
•      Light can not pass through them at all.   
•      For example: Wall, wood, cardboard, meta, some plastics etc.

Q.20. Classify A, B and C on the basis of transparency.
               
Ans.20. A is Opaque as through it we can not be seen at all.
              B is Translucent as through it we can not see clearly but can see partially.
              C is Transparent as through it we can see clearly.
              

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