Grade-8 (Science) :Some useful Chemicals

              Unit :-15   Some Useful Chemicals

1.)Water :

Water: A substance composed of the chemical elements hydrogen and oxygen is called water .It is found  in gaseous, liquid, and solid states. It is one of the most plentiful and essential of compounds.  it has the important ability to dissolve many other substances

Physical properties of water

i)It is a colourless, odourless and tasteless liquid

ii).It is an excellent solvent.

iii)The boiling point of water is 100⁰C and freezing of water is 0⁰C .

iv)At 4⁰C water has maximum density and minimum volume .Chemical properties of water

1)Amphoteric nature:

Water can act as both acid and base, which means that it is amphoteric  in nature.

2. 2)Reaction with alkali metal :When water  react with alkali metal  oxide and hydrogen gas is obtained

Uses of water : It is used for following purpose :

1)Domestic uses of water: It is used for drinking, bathing, cooking food and washing dishes, clothes, fruits, vegetables and brushing teeth.

2.)Water use for agriculture :. It  is used for gardening, farming and fisheries

3)Industrial uses of water: It is e used for creating or to cool the equipment ,washing, cooling, processing, transporting, diluting or fabricating of a product.

Types of water :There are two types of water

1.)Soft water : The water which gives lather easily with soap is called soft water .

For example :Rain water ,distilled water etc.

2.)Hard water :The water which does not produce lather easily with soap is called hard water . For example :Underground water ,water of stream, river etc.

Causes of hardness of water :Hardness of water caused by presence of following soluble salts i.e.

 i)Calcium bicarbonate            i)Temporary  hardness

  ii)Magnesium                               

 

 iii)Calcium chloride

iv) Magnesium chloride              ii)Permanent

 v)Calcium sulphate                hardness

  vi) Magnesium sulphate

Types of hardness of water :There are two types of hardness of water :i)Temporary hardness of water :The hard water caused by the presence of soluble salts i.e. Calcium bicarbonate , and Magnesium bicarbonate is called temporary hardness of water .

ii)Permanent hardness of water :The hardness of water caused by the presence of soluble salt i.e. Calcium carbonate ,Magnesium carbonate ,Calcium chloride and Magnesium carbonate is called permanent hardness of water .

Methods of removal of temporary hardness of water :Temporary hardness of water can be removed by following two methods :

i)By boiling :The temporary hardness of water can be removed by boiling of water because due to boiling soluble  bicarbonate salts are converted into insoluble carbonates which can be removed later by filtration

 ii)By using lime water :Temporary hardness of water can be removed by treating with calculated amount of lime ,because due to lime water soluble bicarbonate salts are converted into insoluble carbonates ,which can be removed by later filtration .This process is known as clark’s method.

Methods of removal of Permanents hardness of water: Permanents hardness of water can be removed by following two methods :

i)By adding washing soda(Sodium Carbonate): Permanent hardness of water can be removed by adding washing soda because it convert soluble chloride and sulphate of Magnesium and Calcium salts into insoluble form which can be removed later by filtration .

ii)By Permutit Method : Permutit is the trade name for an artificially prepared sodium zeolite or sodium aluminium orthosilicate obtained by fusing together sodium carbonate silica and alumina It possesses the higher quality of reactivity with calcium and magnesium ions forming insoluble calcium or magnesium zeolites

Calcium and Magnesium Zeolites being insoluble remains in the tower and soft water free from calcium and magnesium salts is above the permutit .

    

    Advantages of hard water :

i)It contains minerals i.e. calcium and iron that help to maintains strongest of teeth and bones of our body.

ii)Hard water has a better flavor than that of soft water due presence of minerals .

Disadvantages of hard water :

i)Hard water consumes more soap due to less lather .

ii)Hard water is not fit for washing white clothes .

 

2.)Sodium carbonate :It is commonly known as washing soda .It molecular formula is Na₂(CO₃).

Properties :It is white crystalline solid .

ii)It is an alkali .

uses

:i)It is used for manufacturing glass, soap.

ii)It is used for softening hard water .

iii)It is used for making paper ,paints etc.

iv)It is also used for making detergent .

 

3.)Sodium bicarbonate :It is commonly known as  eating soda. It is prepared by passing carbon dioxide through saturated solution of sodium carbonate. Its molecular formula is Na₂(HCO₃).

Properties :

i)it is white solid substance.

ii) It is alkaline in nature .

iii)It is soluble in water .

Uses :

i)It is used in soft drink .

ii)It is used for making medicine .

iii)it is used in fire extinguisher .

 

4.)Glycerol :It is commonly known as Glycerine Its molecular formula is C₃H₅(OH)₃ .

Properties :

i)It is colourless ,and viscous liquid .

ii)It is sweet in taste .

Uses :

i)it is used as sweetening agent .

ii)It is used for making Cosmetic materials .

iii)It is used for treatment of skin and leap cracking .