Preparation and properties of some important compounds - sodium carbonate, sodium chloride, sodium hydroxide and sodium hydrogen carbonate;

Sodium carbonate (Na2CO3)

Sodium carbonate exists as anhydrous (Na2CO3) and also as hydrated salt. The decahydrated salt (Na2CO3.10H2O) is known as washing soda while the anhydrous salt is called soda ash.

Occurrence

Large deposits of this salt occur in Owens lake in California and Lake Magadi in British East Africa. It occurs native as Na2CO3.NaHCO3.H2O in Egypt.

During hot weather, soda is also collected from a large number of alkaline lakes.

Manufacture of Sodium Carbonate

Ammonia-soda process (or Solvay process)

This process is the most popularly used method. As Ernest Solvay, the Belgian chemical engineer, devised it in 1864 it is known as Solvay process.

Raw materials

The raw materials for this process are common salt, ammonia and limestone (for supplying CO2 and quicklime).

Principle

When carbon dioxide is passed into a concentrated solution of brine saturated with ammonia, ammonium bicarbonate is produced,


The ammonium bicarbonate then reacts with common salt forming sodium bicarbonate,

Sodium bicarbonate being slightly soluble (in presence of sodium ions) gets precipitated. The precipitated sodium bicarbonate is removed by filtration and changed into sodium carbonate by heating.

The mother liquor remaining after the precipitation of sodium bicarbonate contains ammonium chloride. This is used to regenerate ammonia (one of the raw materials) by steam heating with milk of lime.


Lime is obtained by heating limestone.


Ammonia and carbon dioxide liberated are utilized in making the whole process cyclic and continuous. The only by-product in the process is calcium chloride.

Sodium chloride (NaCl)

Sodium chloride (NaCl) or common salt is an ionic crystal consisting of equal numbers of sodium and chlorine atoms and is an essential component in the human diet, being found in blood sweat and tears.
Occurrence
Sodium chloride is abundant and can be found naturally occurring. It can be found in the mineral halite (pure rock salt) as well as in mixed evaporates in salt lakes.
Sea water also contains 2.7% by weight salt and constitutes 80% of the dissolved minerals in sea water.
Production
Sodium chloride is mined or obtained from brine, when water is added to salt deposits.
Alternatively, it is obtained from sea water. This is commonly known as sea salt and constitutes most table salt. It also contains some impurities.

Sodium chloride:
• Has a cubic crystalline structure
• Is clear when pure, although may also appear white, grey or brownish, depending upon purity
• Is soluble in water
• Is slightly soluble in other liquids
• Is odourless
• Has a characteristic taste
• Molten sodium chloride is an electrical conductor

Symbol NaCl

Atomic Weight 58.44
Eutectic Composition 23.31% NaCl
Melting Point 801°C
Boiling Point 1465°C
Density 2.17g/cm3
Refractive Index 1.5442
Mohs Hardness 2.5
Co-Efficient of Thermal Expansion @ 0°C 40x10-6
Solubility g/100g H2O at 0°C 35.7


Sodium chloride is used for:
• Windows for analytical instruments
• De-icing
• Food and cooking
• High power lasers
• To produce chlorine and sodium
• Historically it has been used as a form of currency


Sodium hydroxide

sodium hydroxide chemical compound, NaOH, is a white crystalline substance that readily absorbs carbon dioxide and moisture from the air.
It is very soluble in water, alcohol, and glycerin.

It is a caustic and a strong base
It is commonly known as caustic soda, lye, or sodium hydrate.
The principal method for its manufacture is electrolytic dissociation of sodium chloride; chlorine gas is a coproduct.
Small amounts of sodium hydroxide are produced by the soda-lime process in which a concentrated solution of sodium carbonate (soda) is reacted with calcium hydroxide (slaked lime); calcium carbonate precipitates, leaving a sodium hydroxide solution.
The major use of sodium hydroxide is as a chemical and in the manufacture of other chemicals; because it is inexpensive, it is widely used wherever a strong base is needed.
It is also used in producing rayon and other textiles, in making paper, in etching aluminum, in making soaps and detergents, and in a wide variety of other uses.

Sodium Bicarbonate NaHCO-3

Sodium Bicarbonate, commonly called baking soda, is a white odourless, crystalline solid, completely soluble in water but slightly soluble in ethanol. It is the mildest of all sodium alkalis.

It is prepared from purified sodium carbonate or sodium hydroxide solution with passing carbon dioxide which is bubbled into the solution of pure carbonate, and the bicarbonate precipitates out to be dried as the bicarbonate is less soluble than the carbonate.

Sodium bicarbonate is also made as an intermediate product in the Solvay process (described above)which is to make sodium carbonate from calcium carbonate by treating sodium chloride with ammonia and carbon dioxide.

The major use of sodium bicarbonate is in baking powders.
Sodium Bicarbonate plays an important role in the products of many diverse industries with functions of releasing CO2 when heated above about 50 C or when reacted with a weak acid makes sodium bicarbonate a key ingredient in food leavening as well as in the manufacture of effervescent salts and beverages.
It can react as an acid or a base in water treatment.
In health and beauty applications, mild abrasivity and ability to reduce odors chemically by neutralizing the acid by-products of bacteria are utilized.
It is also used in treating wool and silk, fire extinguishers, pharmacy, leather, oredressing, metallurgy, in cleaning preparations and industrial & chemical processe.

Uses

food & food processing, beverages , pharmaceuticals , animal foodstuffs , household cleaning products , rubber & plastics foam blowing , fire extinguishers & explosion suppression , effluent & water treatment, flue gas treatment , oil drilling , industrial & chemical processes