Baking soda , Washing soda, plaster of paris, Bleaching powder.

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 SALTS:

Salts are the ionic compounds which consist of two parts, one part carrying a positive charge called ion or cation.
The other part carrying a negative charge called ion or anion.

Family of salts:

Classification of salts on the basis of Acids from which they are obtained:

• chloride salts:  sodium chloride, potassium chloride, calcium chloride etc.

• Nitrate salts:  sodium nitrate, potassium nitrate, calcium nitrate etc.

• Sulphate salts:  Sodium sulphate, potassium sulphate, calcium sulphate, magnesium sulphate etc.

• Carbonate salts:  sodium carbonate, potassium carbonate, calcium carbonate.

 COMMON SALT ( SODIUM CHLORIDE)

Chemical name of common salt is sodium chloride. Common salt is also known as  
"Table salt" or just salt.

Occurence & Extraction of common salt:

1. common salt from seawater:   seawater contains many salts dissolved in it, most of which is sodium chloride.

2. Common salt from underground:. Common salt is also found in the form of solid deposits in several parts of world. Due to presence of impurities, these large crystals are often brown in colour. This is called "Rock Salt".

Uses of common salt:

• Common salt is used in cooking food. It is essential for our diet.

• Common salt is used as preservative for a number of food materials such as pickles, meat, fish etc.

• Common salt is used to manufacture soap and in preparation of pottery glaze.

• Common salt is used to make freezing mixture by mixing with ice.

     CHEMICALS FROM COMMON SALT

SODIUM HYDROXIDE:

Sodium hydroxide is commonly known as 'caustic soda'. The chemical name formula of sodium hydroxide is " NaOH". It is strong base.

Preparation of sodium hydroxide:

Sodium hydroxide is prepared by electrolysis of an aqueous solution of sodium chloride called brine. The method is called Chlor- alkali process since the products of electrolysis are chlorine and sodium hydroxide. On passing electricity through the aqueous solution of sodium chloride it decomposes to form sodium hydroxide, chlorine and hydrogen.

    2Nacl +      2H2O      ➡   2NaOH +   Cl2+   H2


Uses of Sodium Hydroxide:

• It is used in the manufacture of soaps and detergents.
• It is used in the paper industry.
• It is used for degreasing metals.
• It is used in making of artificial fibres such as rayon etc.
• It is used in purifying bauxite ore from which aluminum is extracted.
• It is used in refining of petroleum.

BLEACHING POWDER 

Chemical name of bleaching powder is calcium oxychloride. It's formula is CaCl2
Though its actual composition is quite complex. It is also known as chloride of lime.

Preparation of bleaching powder:

The chlorine produced during the production of caustic soda is used for manufacture of bleaching powder.
It is produced by action of chlorine gas on dry slaked lime.

Ca(OH)2    +     Cl2     ➡       CaOCl2    +    H2O

Properties of Bleaching powder:

• Colour & State:  Bleaching powder is a yellowish- white powder.
• Solubility in water:  Bleaching powder is soluble in cold water. 
• Action on Air:  When Bleaching powder is exposed to air, it gives smell of chlorine. This is due to the reason that, carbon dioxide present in the air reacts with the Bleaching powder to liberate chlorine.

Uses of Bleaching powder:

• It is used for Bleaching cotton and linen in the textile industry, for Bleaching wood pulp in paper factories.
• It is used for Bleaching washed clothes in laundry.
• It is used for making wool un shrinkable
• It is used for disinfecting drinking water to make it free of germs as chlorine liberated by it can kill the germs.

BAKING SODA:

Chemical name of baking soda is sodium hydrogen carbonate. It's formula is NaCHO3
It is also known as sodium bicarbonate.
The main constituent of baking powder is baking soda .

Preparation of Baking soda:

Baking soda is manufactured on a large scale by reacting a cold and concentrated solution of sodium chloride with ammonia and carbon dioxide . This method is known as ammonia-soda process.

NaCl + H2O + CO2 + NH3    ➡    NH4Cl + NaHCO

Properties of Baking soda:

• colour & State:  Baking soda is a white crystalline solid.
• Action on Air:  Baking soda is stable in Air.
• Solubility in water:  Baking soda is sparingly soluble in water. The solution is basic in nature due to salt hydrolysis.
• Action of Acids:  Baking soda reacts with acids such as HCl etc.. to give out carbon dioxide brisk effervescence.
• Action of heat: When solid sodium hydrogen carbonate is heated or its aqueous solution is heated, it decomposes to give sodium carbonate with the evolution of carbon dioxide gas.

Uses of baking soda:

• In medicines as antacids.
• As additive in food and Drinks.
• In fire Extinguishers.

WASHING SODA:

Chemical name of washing soda is Sodium carbonate. It's formula is Na2CO3 .10H2O. That is , washing soda contains 10 molecules of water of crystallization.

Preparation of Washing soda:

Washing soda is obtained from sodium chloride as one of the starting material. The method consists of the following steps:
• Manufacture of sodium Hydrogen carbonate
• Thermal decomposition of sodium Hydrogen carbonate
• Recrystallization of sodium Hydrogen carbonate.
   Na2CO3    +   10H2O  ➡   NaCO3.10H2O

Properties of Washing soda:

• Colour and State.
• Solubility in Water.
• Action of Air.
• Action of Acids.
• Action of heat.

Uses of Washing soda:

• Washing soda is used as a cleansing agent for domestic purposes such as washing clothes.
• It is used in glass, soap and paper industries.
• It is used in  manufactured of sodium compounds such as borax.
• It is used for removing permanent hardness of water.

PLASTER OF PARIS

Chemical name of plaster of paris (POP) is calcium sulphate hemihydrate. It's molecular formula is CaSO4.1/2H2O.

Preparation of plaster of paris:

Plaster of paris is prepared from gypsum. Gypsum is calcium sulphate dihydrate, calcium sulphate containing 2 molecules of water of crystallization. Gypsum is heated to a temperature of 100°C in a kiln. At this temperature, it loses three-fourth of its water of crystallization and forms plaster of paris.
 
  CaSO4.2H2O  ➡  CaSO4. 1/2H2O  +  1 1/2H2O

Properties of plaster of paris:

• Colour & state:  It is white in powder.
• Reaction with water: when it is mixed with the water and is left for half an hour to one hour, it sets to a hard mass. This is due to rehydration of plaster of paris to gypsum.

Uses of plaster of paris:

• plaster of paris is used in hospitals for fixing broken bones and ligaments. A cast of wet plaster of paris is applied over the affected area to keep it immobile.
• It is helpful in making toys, casts for statues, decorative materials.
• It is used in making the surface smooth, 
For Ex. That of walls, ceiling before painting.






 

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