Caustic Soda

Sodium hydroxide (NaOH), also known as lye and caustic soda, is an inorganic compound. It is a white solid and highly caustic metallic base and alkali of sodium which is available in pellets, flakes, granules, and as prepared solutions at different concentrations. Sodium hydroxide forms an approximately 50% (by mass) saturated solution with water.

Sodium hydroxide is soluble in water, ethanol, and methanol. This alkali is deliquescent and readily absorbs moisture and carbon dioxide in air.

Sodium hydroxide is used in many industries, mostly as a strong chemical base in the manufacture of pulp and paper, textiles, drinking water, soaps and detergents and as a drain cleaner. Worldwide production in 2004 was approximately 60 million tonnes, while demand was 51 million tonnes.

Parameter Value

CAS Number


Chemical formula


Molar mass

39.9971 g mol−1


White, waxy, opaque crystals




2.13 g/cm3

Melting point

318 °C (604 °F; 591 K)

Boiling point

1,388 °C (2,530 °F; 1,661 K)

Solubility in water

418 g/L (0 °C)
1110 g/L (20 °C)
3370 g/L (100 °C)


soluble in glycerol
negligible in ammonia
insoluble in ether

Solubility in methanol

238 g/L

Solubility in ethanol

<<139 g/L

Vapor pressure

<2.4 kPa (at 20 °C)

Basicity (pKb)

−0.93[5](NaOH(aq) = Na+ + OH–)

Magnetic susceptibility (χ)

−16.0·10−6 cm3/mol

Refractive index (nD)


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