Caustic soda or sodium hydroxide is a white solid substance with the chemical formula of NaOH and it is resulted from the process of electrolysis of sodium chloride soluble in the electrolytic vessels. It is called caustic soda because it is highly corrosive in nature. It is available in many forms in the industry, and the most common forms are caustic soda flakes and caustic soda pearls. Pure Caustic soda is a colorless crystalline solid that melts at 318 °C without decomposition. It is highly soluble in water, with a lower solubility in polar solvents such as ethanol and methanol.

Similar to the hydration of sulfuric acid, dissolution of caustic soda flakes in water is a highly exothermic reaction where a large amount of heat is released, posing a threat to safety through the possibility of splashing. The resulting solution is usually colorless and odorless. As with other alkaline solutions, it feels slippery with skin contact due to the process of saponification that occurs between NaOH and natural skin oils.

Caustic soda is industrially produced as a 50% solution by variations of the electrolytic chloralkali process. Chlorine gas is also produced in this process. Solid sodium hydroxide is obtained from this solution by the evaporation of water. Solid sodium hydroxide is most commonly sold as flakes, pills, and cast blocks.

Caustic Soda Flakes - Purity-97-2
Caustic Soda Flakes – Purity-97-2
Characteristic Unit Normal Range
(Grade A)
Test Method
Purity as NaOH Wt % 97± 2 JIS K 1200
Carbonates as Na2CO3 Wt % 1 Max JIS K 1200
Chlorides as NaCL Wt % 0.06 Max ASTM E 291
Sulfates as Na2SO4 Wt % 0.01 Max ASTM E 291
Silicates as SiO2 Wt % 0.02 Max IS 252
Aluminum as Al2O3 Wt- ppm 20 Max ISO 10566
Iron as Fe2O3 Wt- ppm 30 Max ASTM E 291
Insoluble in Water Wt% 0.1 Max BSI 6075
Arsenic as AS2O3 Wt- ppm 2 Max IS 9831

Caustic Soda Flakes - Purity-98
Caustic Soda Flakes – Purity-98
Characteristic Unit Test Result
Purity as NaOH %w/w 98 Min
Carbonates as Na2CO3 %w/w 1 Max
Chlorides as NaCL ppm 100
Irons as Fe2O3 ppm 8
Hg ND*
Insoluble Materials %w/w <0.1
Heavy(As,Pb,Hg) ND*

Caustic Soda Flakes - Purity-99.05
Caustic Soda Flakes – Purity-99.05
Characteristic Unit Test Result Accepting Limit Test Method
Purity as NaOH Wt % 99.05 97 Min JIS K 1200
Carbonates as Na2CO3 Wt % 0.24 1 Max JIS K 1200
Chlorides as NaCL Wt % 0.02 0.06 Max ASTM E 291
Sulfates as Na2SO4 Wt % 0.0045 0.01 Max ASTM E 291
Silicates as SiO2 Wt % 0.005 0.02 Max IS 252
Aluminum as Al2O3 mg/Kg <20 20 Max ISO 10566
Heavy Metals as Pb mg/Kg <20 20 Max ISIRI – 364
Iron as Fe2O3 mg/Kg 9.98 30 Max ASTM E 291
Insoluble in Water W% 0.03 0.1 Max BSI 6075
Copper as Cu mg/Kg <2 2 Max ISIRI – 364
Manganese as Mn mg/Kg <1 1 Max ISIRI – 364


  • Bulk
  • Flexi Tank
  • Drum

Properties of Caustic Soda 

Caustic soda is divided into three forms:

  • Liquid NaOH (produced by dissolution of solid sodium hydroxide in water)
  • Flake caustic soda (flaked forms)
  • Solid caustic soda (granular or powdered forms)

In pure form, caustic soda is a waxy and white solid product, which is the most typical of the strong alkalis and a very important industrial chemical as a strong base. Although there is no danger of exploding or igniting, it reacts with various acids (such as hydrochloric acid). It is highly hygroscopic and deliquescent, absorbs not only the moisture to form an aqueous solution, but also carbon dioxide or sulfur dioxide in the air.

Properties of Caustic Soda are listed below:

  • Molecular formula: NaOH
  • Molecular weight: 40.00
  • Specific gravity: 1.48 (45% concentration) 1.50 (50% concentration)
  • Melting point: 9℃ (45% concentration)
  • Boiling point: 136~137℃ (45% concentration)
  • Vapor pressure: 3.24 mmHg (20℃, 45% concentration)

Today there are generally three regular ways to produce Caustic soda:

  • Membrane cell process
  • Diaphragm cell process
  • Mercury cell process

Application of Caustic Soda 

Industries application which Caustic Soda is used:

  • Chemical industry
  • Pulp and Paper industry
  • Detergent and soap industries
  • Aluminum industries
  • Petroleum and natural gas extraction
  • Plastic industry
  • Pesticides
  • Industrial solvents
  • Water treatment
  • Food industry
  • Leather and textiles industries
  • Paint industry
  • Other applications such as: domestic bleaches; flame-retardants; refrigerants; insulation; computer chips; hospital disinfectants, pharmaceuticals, alcohol, and sanitation industries; neutralization and battery making among the others.

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