Sodium Hydroxide

Last Updated: April 28, 2024

Sodium Hydroxide

Sodium hydroxide, also known as lye or caustic soda, is a powerful base commonly used in various industries and everyday products. This white, solid compound is highly soluble in water, producing heat upon dissolution. It plays a crucial role in manufacturing paper, soap, and detergents, and is also used in water treatment processes to help neutralize acids and control water acidity. Despite its many uses, sodium hydroxide must be handled with care due to its ability to cause severe burns upon contact with skin, necessitating safety precautions during use. This compound’s versatility makes it a staple in both industrial applications and household cleaning tasks, highlighting its importance in science and industry.

What is Sodium Hydroxide?

Sodium hydroxide is commonly known as lye or caustic soda and it is a highly versatile and powerful base widely used in various industries. It is a chemical compound with the formula NaOH and appears as a white, odorless solid that readily absorbs moisture from the air. This strong base is essential in the production of paper, textiles, soaps, and detergents. In chemistry, bases like sodium hydroxide are substances that can accept hydrogen ions and neutralize acids, which makes them fundamental in processes requiring pH regulation. Its ability to react with fats and oils helps in creating cleaning agents and also in processing some foods. Despite its usefulness, it must be handled with care due to its corrosive nature, which can cause severe burns upon contact with skin.

Chemical Names and Formulas

Hill FormulaHNaO
NameSodium hydroxide
Alternate NamesAetznatron, Ascarite, Caustic Soda, Collo-Grillrein, Collo-Tapetta, Lye, Soda Lye, Sodium Hydrate, White Caustic

Structure of Sodium Hydroxide


Sodium hydroxide, also known as NaOH, has a simple yet fundamental chemical structure in the world of chemistry. It is composed of sodium ions (Na⁺) and hydroxide ions (OH⁻) held together by ionic bonds. In its solid state, sodium hydroxide forms a crystalline structure, which means the ions are arranged in a specific and orderly pattern. This arrangement allows it to dissolve readily in water, where the sodium and hydroxide ions separate and move freely. This dissociation is crucial for its function as a base, enabling it to react with acids and other substances effectively. Its ionic nature and strong base properties make it essential for a wide range of industrial and laboratory applications.

Preparation of Sodium Hydroxide

Sodium hydroxide, commonly known as lye, can be produced using several methods, but one of the most common and efficient is through the electrolysis of salt water, a process known as the chloralkali process. This method involves passing an electric current through a solution of sodium chloride (common table salt dissolved in water). The chemical reaction that occurs breaks down the salt into its components.

The chemical equation for this process is:

2 NaCl(aq) + 2 H₂O(l) → 2 NaOH(aq) + Cl₂(g) + H₂(g)

In this reaction, chlorine gas (Cl₂) is released at one electrode (anode), and hydrogen gas (H₂) is released at the other electrode (cathode), while sodium hydroxide remains in solution. This method not only produces sodium hydroxide but also valuable chlorine and hydrogen gases, which are used in various industrial applications. This electrolytic approach is favored for its efficiency and ability to produce high-purity sodium hydroxide, crucial for its many uses in industries ranging from manufacturing to cleaning products.

Physical Properties of Sodium Hydroxide

AppearanceWhite, odorless, crystalline solid
SolubilityHighly soluble in water, forms a heat-generating solution
Melting Point318°C (604°F)
Boiling Point1,388°C (2,530°F)
Density2.13 g/cm³ at 20°C (68°F)
pHVery high, typically around 14 when in solution
Thermal StabilityStable up to its melting point but decomposes upon heating above

Chemical Properties of Sodium Hydroxide

Reactivity with Acids

  • Sodium hydroxide is a strong base, meaning it reacts vigorously with acids to form water and a salt. This type of reaction is known as a neutralization reaction. The below equation shows how sodium hydroxide reacts with hydrochloric acid to produce sodium chloride (table salt) and water.
  • Equation: NaOH (aq) + HCl (aq) → NaCl (aq) + H₂O (l)

Reaction with Aluminum

  • Sodium hydroxide reacts with aluminum and water to produce hydrogen gas. This reaction is often used to demonstrate the production of hydrogen. The hydrogen gas produced can be tested by its pop sound when a lit splint is introduced.
  • Equation: 2 Al (s) + 2 NaOH (aq) + 6 H₂O (l) → 2 NaAl(OH)₄ (aq) + 3 H₂ (g)

Saponification Reaction

  • One of the well-known reactions of sodium hydroxide is saponification, where it reacts with fats or oils to form soap. This process involves breaking down the ester bonds in fats to form glycerol and soap (sodium salts of fatty acids).
  • Equation: Fat + NaOH → Glycerol + Sodium Salt of Fatty Acid (Soap)

Ability to Absorb Carbon Dioxide

  • Sodium hydroxide can absorb carbon dioxide from the air, forming sodium carbonate.This property is useful in carbon dioxide scrubbing processes used in industries and breathing apparatus.
  • Equation: 2 NaOH(s) + CO₂(g) → Na₂CO₃(s) + H₂O(l)

Sodium Hydroxide (NaOH) Chemical Compound Information

Chemical Identifiers

CAS registry number1310-73-2
PubChem compound ID14798
SMILES identifier[OH-].[Na+]
InChI identifierInChI=1/Na.H2O/h;1H2/q+1;/p-1/fNa.HO/h;1h/qm;-1
MDL numberMFCD00132264

NFPA Label

NFPA health rating4
NFPA fire rating0
NFPA reactivity rating4

Uses of Sodium Hydroxide


Soap and Detergent Manufacturing

Sodium hydroxide is critical in the production of soaps and detergents. It reacts with fats and oils in a process called saponification to create soap. This reaction transforms triglycerides into glycerol and fatty acid salts, which are the cleansing agents in soaps and detergents.

Paper Industry

In the papermaking process, sodium hydroxide is used to separate cellulose fibers from lignin, the ‘glue’ that holds the wood fibers together. This chemical is essential for breaking down wood into pulp, leading to the production of smoother, higher-quality paper.

Water Treatment

Sodium hydroxide plays a crucial role in water treatment facilities. It is used to adjust the pH level of water, making it more alkaline to facilitate the removal of impurities and heavy metals through precipitation.

Food Processing

In the food industry, sodium hydroxide is used in the cleaning and sanitation process of equipment. It’s also employed in the pretreatment of certain foods, like olives, which are soaked in a lye solution to soften them and reduce bitterness.

Chemical Manufacturing

As a reagent, sodium hydroxide is instrumental in various chemical reactions. It is used to produce an array of chemicals, including solvents, plastics, synthetic fibers, and bleach.

Side Effects of Potassium Hydroxide

  • Skin Irritation: Direct contact with sodium hydroxide can cause severe skin irritation or burns. Even a diluted solution can irritate the skin, leading to redness, pain, and in severe cases, chemical burns.
  • Eye Damage: Sodium hydroxide is extremely hazardous to the eyes. Exposure can result in redness, severe pain, blurred vision, or even permanent eye damage including blindness, depending on the concentration and duration of exposure.
  • Respiratory Issues: Inhalation of sodium hydroxide dust or mist can lead to respiratory difficulties. It can irritate the mucous membranes in the respiratory tract, causing coughing, wheezing, and shortness of breath.
  • Ingestion Hazards: Accidental ingestion of sodium hydroxide can be extremely dangerous. It can cause severe burns in the mouth, throat, esophagus, and stomach, leading to difficulty swallowing, chest pain, and in severe cases, perforation of the gastrointestinal tract.
  • Systemic Effects: Beyond its immediate burn potential, prolonged exposure to sodium hydroxide can lead to systemic health issues such as hair loss, low blood pressure, and in severe cases, shock.


Is Sodium Hydroxide Harmful to Humans?

Yes, sodium hydroxide can be very harmful, causing severe skin burns, eye damage, and respiratory issues if mishandled.

Is Sodium Hydroxide Same as Baking Soda?

No, sodium hydroxide (NaOH) and baking soda are different compounds with distinct chemical properties and uses.

What Are the Risks of Sodium Hydroxide?

The risks include severe burns, respiratory problems, eye injuries, and systemic effects if ingested or improperly handled.

Is Sodium Hydroxide Just Salt Water?

No, sodium hydroxide is a strong alkaline compound, not just salt water, which typically refers to a solution of sodium chloride (table salt) in water.

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