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Sodium hydroxide

Chemistry Formulas

About Sodium hydroxide

Sodium hydroxide breaks down the proteins of the skin flesh to a pasty mass, therefore it is commonly known as caustic soda.In the manufacturing of sodium metal, soap, rayon, paper, dyes and drugs. For mercuring cotton to make cloth unshrinkable and reagent in lab. 

Sodium hydroxide (Caustic soda),NaOH

Preparation of  Sodium hydroxide

(a) Gossage process : Check this method in the following Pdf.

(b) Electrolytic method : Caustic soda is manufactured by the electrolysis of a concentrated solution of  At anode: Cl- discharged;  At cathode: Na+ discharged Caster – Kellner cell (Mercury cathode process) of preparation of Sodium hydroxide

1.This process is used to avoid reaction between NaOH and Cl2.

2.NaOH is obtained by the electrolysis of aqueous solution of NaCl (brine).

3.The cell has three compartments and involves following reactions.

Description:

1.Castner – Kellner cell is the most widely used mercury –cathode type cell.  

2.It consists of a large rectangular iron tank divided into three compartments by means of non-porous slate partitions.  These partitions do not touch the bottom of the cell.  

3.A layer of mercury at the bottom of the cell separates the three compartments from one another.  

4.The one end of the cell is pivoted, while the other rests on an eccentric (induction) wheel which gives a rocking motion to the whole cell keeping the mercury in circulation.  

5.The two outer compartments of the cell are fitted with fixed graphite anodes and are filled with saturated brine solution.  

6.The middle compartment is fitted with a series of iron rods acting as cathode and is filled with a dilute solution of caustic soda.  

7.Mercury layer acts as cathode in the two outer compartments and as anode in the middle compartment due to induction.

8.On passing electric current, brine solution is electrolysed in both the outer compartments. 

9.Chlorine is evolved at the anodes, while the sodium ions are discharged at the mercury layer and form sodium amalgam.  Here, H+ ions are not discharged at the cathode because of the high overpotential of hydrogen over mercury.

10.The sodium amalgam so produced flows to the middle compartment due to the rocking motion of the cell and reacts with water to form sodium hydroxide.

11.When the concentration of sodium hydroxide solution in the middle compartment is about 20%, it is drawn out, evaporated, fused and cast into sticks.

c)  Kellner – Solvay Cell method of prepartion of Sodium hydroxide

1.The cell has replaced Castner – Kellner cell to some extent.  Kellner – Solvay cell consists of a rectangular trough, at the base of which there is a thin layer of mercury which flows from one end to the other acting as cathode.  

2.A concentrated brine solution flows slowly through the cell in the same direction as the mercury and is maintained at a constant level.

3.The graphite anodes are suspended into the brine.  During electrolysis, Cl ions are oxidized at the anode and chlorine gas goes out of the cell, while sodium ions are reduced at the mercury cathode forming sodium amalgam.

4.The sodium amalgam leaves the cell on the left and flows into an iron tank where it is decomposed by calculated amount of water giving caustic soda, mercury and hydrogen.

Outer compartment – Brine solution is electrolysed ; Central compartment – 2%   solution and  

Properties of Sodium hydroxide 

White crystalline solid, highly soluble in water, It is only sparingly soluble in alcohol. The below given pdf consist of all the chemical properties of Sodium hydroxide.

i) It is a hygroscopic, deliquescent white solid which absorbs CO2 and moisture from the atmosphere. 2NaOH + CO2  Na2CO3 + H2O

ii) M.P = 3180C

iii) It is highly soluble in water and considerable amount of heat is evolved due to the formation of a number of hydrates.  e.g., NaOH. H2O (mp 6400C), NaOH 2H2O (mp 12.70C), NaOH, 7H2O (mp=?)

iv) It is soapy to touch, when it falls on skin, it decomposes the muscle proteins and makes a pulp.  (Therefore it is called caustic soda).

Uses of Sodium hydroxide

i) In the prepeartion of soap, paper, viscon ray on (artificial silk), organic dyestuffs, Na – metal and many other chemicals like sodalime.

ii) In the refining of petroleum and vegetable oils.  

iii) As a cleansing agent and in washing powder, for cleaning machines and metal sheets glassware in laboratory.

iv) In purification of bauxite for the extraction of ‘Aluminium’.

v) It used for mercerizing cotton.

vi) As an important reagent in laboratory.

vii) It used to absorb SO2 from the atmosphere near electrical generators.

viii) In reclaiming rubber.

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Find the pdf of chemical Properties of Sodium hydroxide

Sodium hydroxide

Sodium hydroxide

Sodium hydroxide

Sodium hydroxide

Sodium hydroxide

Sodium hydroxide

Sodium hydroxide

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