Sodium Hydroxide : Prepaeation , Physical & Chemical reaction , assay , storage , and uses.

 

 Sodium Hydroxide

           [NaOH]


Sodium Hydroxide contains not less than 97 % of total alkali calculated as sodium hydroxide and not more than 2.5 % of sodium carbonate.

Preparation

When milk of lime is added to hot sodium carbonate solution 20% sodium hydroxide and precipitate of calcium carbonate obtained the reaction is reversible.

Na₂CO₃ + Ca(OH)₂ → 2NaOH + CaCO₃↓

  The precipitated calcium carbonate is separated the clear liquid containing Sodium Hydroxide is evaporated and the molten product is converted into sticks , pellets or masses.


Electrolytic method

Sodium Hydroxide is manufactured by the electrolysis of sodium chloride for the purpose of Mercury diaphragm celk, known as castner - kellner cell, is used . It consists of a large rectangular through with a layer of Mercury at the bottom sodium is electrolysed from a concentrated brine solution with a graphite anode and a Mercury cathode to produce a dilute sodium amalgam . the amalgam reacts with water to form a dilute hydroxide solution in cathode compartment in pure form .
Hydrogen and chlorine are the useful by product at the anode .

At cathode
Na+    →    Na
   2Na  +  2H₂O →  2NaOH  +  H₂

At anode
 Cl−   →  Cl
    Cl  +  Cl  →  Cl₂

Sodium hydroxide solution is removed periodically and water added. the concentrated solution is evaporated to get fused sodium hydroxide.

Physical property

* it is a white solid highly deliquescent and had tendency for atmospheric carbon dioxide. 

*It is very soluble in water springly in alcohol , corrosive nature.

* it has melting point 318° .

* it is hard and brittle and shows are crystalline fracture.

Chemical Property

* Sodium Hydroxide is a strong alkali. it changes the colour of indicator and neutralize all acids or acid oxides producing salts.

NaOH  +  HCl  →  NaCl  +  H₂O

Sodium Hydroxide is highly ionized in solution making it one of the strongest base available.

* ammonium Salts decomposed with sodium hydroxide and form ammonia.

NH₄Cl  +  NaOH  →  NaCl  +  NH₃↑  +  H₂O


Chemical incompatibility

Sodium Hydroxide is a strong base which can be assayed by titrimetry. The procedure involved titrating a solution containing a weighed sample of NaOH with 1N sulphuric acid two endpoints are determined.

Pharmaceutical uses

* it is used in pharmaceutical laboratory for example titration.

* it is due to the manufacture of fabric paper and soap.

* it is used to neutralized acid.

* it is used as treating water .

*A 2.5% solution in glycerol is used as a cuticle solvent and to remove warts.

* Ad escharotic preparation of sodium hydroxide and calcium oxide known as London paste is used for adjusting the pH of solution .

*NaOH solution are used to neutralize acid and make Sodium salt to treat cellulose in making viscose Ryon and cellophane .


Storage condition


It is stored in a well closed container because it absorb moisture and carbon dioxide.








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