Sodium Hydroxide, also known as lye or caustic soda, is an inorganic compound with the chemical formula NaOH. It is a highly caustic metallic base and alkali salt that forms a strongly alkaline solution in water. Caustic soda occurs as a deliquescent white solid that readily absorbs moisture from air to form a strongly alkaline solution.

Physical and Chemical Properties

Caustic soda has a molecular formula of NaOH and a relative molecular mass of 40.00 g/mol. It exists as odorless white crystals or as white opaque pellets at room temperature. Caustic soda is very soluble in water and forms a highly alkaline caustic soda solution that turns red litmus blue. The saturated aqueous solution of caustic soda is referred to as lye and has pH of approximately 13.15. Caustic soda is stable in dry air but absorbs moisture and carbon dioxide when exposed to humid air, forming a white precipitate layer on its surface. It has a melting point of 318°C and decomposes when heated to higher temperatures. Caustic soda reacts vigorously with many acids, generating heat and evolving hydrogen gas.

Production of Caustic soda

The Sodium Hydroxide  main industrial production method for caustic soda involves the electrolysis of a concentrated sodium chloride solution. In this process, known as the chloralkali process, sodium chloride (NaCl) solution is electrolyzed in a cell containing a diaphragm and electrodes. Oxygen gas is produced and removed at the anode while chlorine gas is generated at the cathode. Caustic soda is then produced as an aqueous solution at the cathode. Some caustic soda is also produced from the reaction of soda ash (sodium carbonate) with calcium hydroxide in the Mannheim process.

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