Sodium Hydroxide


Sodium Hydroxide is an inorganic compound with the chemical formula NaOCl. This powerful base is a simple ionic compound of sodium with a hydroxide ion – a negatively charged combination of single oxygen and hydrogen atoms. Also known as L-Y-E and caustic soda it is the strongest alkali you are likely to come across in everyday use.

Looking back into the origins of the word ‘lye’ the oldest name for sodium hydroxide, it comes from an old English word meaning ‘wash stuff’. The term ‘lye’ was commonly used as a term for strong soap from the 13th century onwards. Sodium hydroxide is extremely corrosive and needs to be handled with care.

The ancient Egyptians and the Babylonians used this compound long before it was identified.

They would manufacture of a weak solution by percolating vegetable ashes with water. At the time, they had no clue what they were using and it was only later that a clear identification of the nature of the substance was made when Humphrey Davy discovered the element sodium, which he produced by electrolysing molten sodium hydroxide in 1807.

In more modern times, Sodium Hydroxide, a very corrosive chemical, is used to manufacture soaps, rayon, paper, explosives, dyestuffs, and petroleum products and as a bleaching agent in the textile, detergents, and paper and pulp industries. In the home, sodium hydroxide is often used to unblock drains. It interacts with fats (that usually cause the blockage) and converts them into a soluble material. The same process is used in industrial cleaning, where a hot sodium hydroxide solution is used to degrease machinery and storage tanks.

Sodium Hydroxide itself is a white solid when stored at room temperature and has a waxy consistency.

When produced, it is usually as pellets or flakes. Because is it hygroscopic (meaning it absorbs water and carbon dioxide from the air), it needs to be stored in airtight containers. Its hygroscopic nature also means that when it is dissolved intentionally in water it dissolves very easily but does give off a fair amount of heat as it dissolves.

Sodium hydroxide is a highly caustic base and alkali that decomposes proteins at ordinary ambient temperatures and may cause severe chemical burns. It forms a series of hydrates NaOH·nH. The monohydrate NaOH·H 2O crystallises from water solutions between 12.3 and 61.8 °C.
The commercially available “sodium hydroxide” is often this monohydrate, and published data may refer to it instead of the anhydrous compound.

Most sodium hydroxide is produced by electrolysing sodium chloride solution, giving off chlorine and hydrogen and leaving sodium hydroxide in solution. The world consumes 50 to 60 million tonnes of the compound every year.