Sodium hydroxide

Sodium hydroxide, also called caustic soda and lye, is an important chemical with the formula NaOH. It is a white solid made from sodium and hydroxide ions. It is very strong and can break down some materials, so it can be dangerous if not handled carefully.

This compound mixes easily with water and can absorb moisture and carbon dioxide from the air. It is often used in schools to show how acids and bases work, especially with hydrochloric acid and neutral water.

Sodium hydroxide is used in many everyday products and industries. It helps make paper, textiles, drinking water, soaps, detergents, and drain cleaners. It is very important in many different areas.

Properties

Sodium hydroxide is a white solid. It melts at 318 °C and boils at 1,388 °C. It mixes well with water and feels slippery on the skin because it turns skin oils into soap-like substances.

When sodium hydroxide dissolves in water, it releases heat, which can be dangerous. The solution is usually clear and has no smell. The thickness of the solution changes with temperature. It becomes thinner when it gets warmer. Sodium hydroxide can form different structures when mixed with water, depending on the temperature and amount used. These structures are called hydrates.

Production

Sodium hydroxide is made in factories. It is created as a solution and then turned into solid pieces or blocks. Chlorine gas is made during this process.

In 2022, about 83 million tons of sodium hydroxide were made around the world. In the United States, companies like Olin make a lot of it using special methods.

In the past, sodium hydroxide was made by mixing sodium carbonate with calcium hydroxide. Today, the chloralkali process is used instead.

Sodium hydroxide can also be made by mixing pure sodium metal with water. This creates hydrogen gas and heat. This method is mostly used for science demonstrations and not for making large amounts.

Uses

See also: Hydrodesulfurization

Sodium hydroxide is a strong base used in many industries. It helps make salts, detergents, and change acidity in chemical reactions. It is often used as a liquid because it is easier to handle.

Sodium hydroxide is used where we need to make things more basic or neutralize acids. For example, in oil drilling, it helps control mixtures and neutralize gases. It is also used to balance acidity in testing and clean up impurities from oil.

Other common uses of sodium hydroxide include:

• Making soaps and detergents. It is used for solid bar soaps, while potassium hydroxide is used for liquid soaps. Sodium hydroxide is more often used because it is cheaper.
• Clearing drains by breaking down fats and grease.
• Making artificial fibres like rayon.
• In making paper. About half of all sodium hydroxide made is used in this way.
• Purifying bauxite ore to make aluminium. This is called the Bayer process.
• Cleaning metals.
• In oil refining.
• Making dyes and bleaches.
• In water treatment plants to adjust acidity levels.

Chemical pulping

Main article: Pulp (paper)

Sodium hydroxide is used to make paper from wood. It helps separate the useful parts of wood from the parts we don’t want. It is important in later steps of making paper, where it helps clean the material.

Tissue digestion

Sodium hydroxide can be used to break down animal tissues. It is important to handle this chemical carefully because it can burn skin and eyes.

Dissolving amphoteric metals and compounds

Sodium hydroxide can dissolve certain metals like aluminium by reacting with them and water to produce hydrogen gas. This reaction is used in cleaning and finishing metal surfaces.

Esterification and transesterification reagent

Sodium hydroxide is used in making soap and biodiesel. It helps create the right conditions for these reactions.

Skincare ingredient

Sodium hydroxide is used in small amounts in some skin products to balance acidity levels.

Food preparation

Sodium hydroxide is used in food for cleaning fruits and vegetables, processing chocolate, making caramel color, and in making certain foods crisp. It is used in making pretzels, some Chinese foods, and olives softer.

Cleaning agent

Sodium hydroxide is used to clean industrial equipment and household drains. It breaks down grease and oils. It is important to handle it carefully because it can burn skin and eyes.

Relaxer

Sodium hydroxide is sometimes used in products to straighten hair, but it is mainly used by professionals because it can cause burns.

Paint stripper

Sodium hydroxide was once commonly used to remove paint from wood, but it can damage the wood and is less used today.

Water treatment

Sodium hydroxide is used to adjust the acidity of water to protect pipes and reduce the amount of harmful metals that can dissolve into drinking water.

Historical uses

Sodium hydroxide was once used to help detect carbon monoxide poisoning by changing the color of blood samples. Today, other methods are used.

In cement mixes, mortars, concrete, grouts

Sodium hydroxide is used in some cement mixes to help make them more even and easier to work with.

Safety

Like other strong acids and alkalis, even a few drops of sodium hydroxide can hurt living tissues. It may cause chemical burns or blindness if it touches the eyes. Solid sodium hydroxide can also be unsafe if there is moisture nearby. Always wear protective equipment, such as rubber gloves, safety clothing, and eye protection, when handling this chemical. If it gets on your skin, rinse it off with lots of water for at least ten to fifteen minutes.

When sodium hydroxide mixes with water or reacts with acids, it can create heat. This heat can burn the skin or start fires. It can also damage glass and react with metals like aluminium, making flammable hydrogen gas. Sodium hydroxide can affect fish and change water’s pH, but it usually does not harm the environment long-term because it becomes neutral quickly.

Storage

Sodium hydroxide must be stored carefully, especially when used in large amounts. It is often kept in small bottles for labs, medium containers for transport, or very large tanks for factories.

It should be stored in special airtight containers to stop it from absorbing moisture and carbon dioxide from the air. Common storage materials include polyethylene, carbon steel, polyvinyl chloride, stainless steel, and fiberglass reinforced plastic.

History

Sodium hydroxide was first made by people who made soap a long time ago. An old book from the late 1200s in Yemen described how to make it. The book explained how to mix water with a special kind of ash from saltwort plants and calcium oxide, which creates sodium hydroxide.

Later, in 1791, a French scientist named Nicolas Leblanc created a way to make a different chemical called sodium carbonate more easily. By the 1900s, scientists started using a process called the electrolysis of sodium chloride to make sodium hydroxide instead.