What is Sodium Hydroxide?

by Lucy Bell-Young

Also known as caustic soda or lye, sodium hydroxide is a diverse chemical compound that is used in the manufacture of everyday products like soaps, detergents and paper. It was even used by a famous serial killer to help destroy the evidence…


Sodium hydroxide is an inorganic, white solid that is strongly alkaline. As an ionic compound, it is comprised of sodium cations (Na+) and hydroxide anions (OH-). It has a range of chemical properties:

  • Its chemical formula NaOH shows the presence of sodium and hydroxide ions
  • Pure sodium hydroxide appears as a colourless crystalline solid
  • Melts at 318°C without decomposition
  • Undergoes saponification when it comes into contact with skin
  • A deliquescent compound as it readily absorbs moisture from the air
  • Highly soluble in water but has lower solubility in polar solvents like ethanol and methanol
  • Insoluble in non-polar solvents like ether
  • Has a highly exothermic reaction when dissolved in water
  • Decomposes proteins at room temperature
  • Can cause severe burns due to it being a caustic base

Different Forms

Sodium hydroxide is available in many different forms. It can be sold as sodium hydroxide pearl, flakes, pellets and even cast blocks. When supplied in bulk, it most commonly appears as an aqueous solution because this is cheaper to produce and handle.

Whatever form it is in, sodium hydroxide still has the ability to cause severe burns so safety precautions must always be taken when handling this compound.

Sodium hydroxide forms several different hydrates, all of which have varying ranges of temperature and concentration. Some of the known hydrates of sodium hydroxide include:

  • Heptahydrate (NaOH.7H2O): this contains seven water molecules
  • Pentahydrate (NaOH.5H2O): this contains five water molecules
  • Dihydrate (NaOH.2H2O): this contains two water molecules
  • Monohydrate (NaOH.H2O): this only contains one water molecule

Of these hydrates, only monohydrate has a stable melting point. It is also the most widely available hydrate. In fact, if you buy the commercially labelled ‘sodium hydroxide,’ you are most likely buying this monohydrate form.

Sodium hydroxide: a soap bubble on a girl's palm
When sodium hydroxide comes into contact with skin, it feels slippery. This is because it undergoes saponification when it reacts with natural oils. Saponification is a process that produces soap. It is important to note that sodium hydroxide should not be handled in this way, however, because it can cause chemical burns.


Sodium hydroxide can be produced using several different methods. Most popular is the electrolytic chloralkali process, where sodium hydroxide is produced as a 50% solution. When the solution is evaporated, solid sodium hydroxide can be obtained.

What Are the Uses of Sodium Hydroxide?

As a popular strong base, sodium hydroxide has a wide range of uses across many different industries. It is commonly used as a pH regulator because it can neutralise acids.

It also reacts with weak acids, like hydrogen sulphide, on a given substrate to produce sodium salts, which can be easily removed. This process is called caustic washing, and it is used to remove sulphurous impurities from things like crude oil. But NaOH is much more than a pH regulator.

Soaps and Detergents

Another very common use for sodium hydroxide is in the manufacture of soap and cleaning products, including detergents and drain cleaners. When producing soap, it is used as an esterification reagent, and chlorine bleach can also be made from a mixture of sodium hydroxide and chlorine.

In drain cleaners, sodium hydroxide is able to convert fats and grease into soap via saponification. The soap is then easily removed by water. Its ability to effectively dissolve fat and grease deposits makes sodium hydroxide an excellent stainless steel and glass cleaner.

As an industrial cleaning agent, it is often referred to as ‘caustic.’ When used in this way, sodium hydroxide is added to water and then heated. It is then used to clean special equipment as well as storage tanks and water discharge pipes.

Chemical Pulping

In the paper-making process, NaOH is used in the pulping of wood. To do this, a mixture of sodium hydroxide and sodium sulphide is used to treat wood, dissolving any unwanted material in order to obtain pure cellulose. This is then used as the basis of the paper.

Sodium hydroxide is also used to regenerate fibres in paper so that it can be recycled. NaOH can separate any ink from the paper fibres, allowing the paper to be recycled and reused.

Food Processing

The main use of sodium hydroxide in the food industry is in the chemical peeling of fruits and vegetables like tomatoes. This is mainly done to prepare the foods for canning.

NaOH is also used to help brown German pretzels, which are soaked in a solution of cold of sodium hydroxide before baking. This gives the pretzels their signature crunch we all know and love. Even bagels are soaked in a lye solution before being baked because it contributes to their shiny surface.

Food grade lye-water, ‘lye’ being another term for sodium hydroxide, is commonly used in Chinese food. It is what gives moon cakes their crunch and also why Chinese noodles often appear yellow, although many people mistake this for the presence of egg.

Other Uses

There are a variety of applications that sodium hydroxide is well-suited towards:

  • In the energy sector, it is used in fuel cell production
  • In pharmaceuticals, it is used in a range of medicines, from simple pain-relievers to anticoagulants and treatments that reduce cholesterol
  • In water treatment facilities it helps to control the acidity of the water
  • In aluminium ore processing it helps to extract alumina from minerals
  • It is an esterification and transesterification reagent in the manufacture of products like soap and biodiesel
  • It is used in tissue digestion as it can break the bonds in the flesh, turning the body into liquid. This is mainly used to decompose roadkill but serial killers have also used this method to dispose of their victims
Polished glass wall reflecting city
Sodium hydroxide is a brilliant glass cleaner because of its ability to dissolve through fat and grease

At ReAgent, we have a huge variety of sodium hydroxide products available to buy. Whether you need it in pearl form or as a specific concentration, we’ve got the solution that’s right for you – and they’re all backed by a 100% quality guarantee so you can buy with confidence.


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