NaOH — Sodium Hydroxide
Sodium hydroxide (NaOH), also known as caustic soda or lye, is a highly corrosive strong base used in chemical manufacturing, soap making, water treatment, and laboratory analysis.
Interactive 3D Molecular Structure — NaOH
Properties
| Chemical Formula | NaOH |
|---|---|
| Molecular Mass | 40.00 g/mol |
| Physical State | Solid (Crystalline or Flakes) |
| Melting Point | 318°C |
| Boiling Point | 1388°C |
| Density | 2.13 g/cm³ |
| pH | 13–14 (1 M solution) |
| Odor | Odorless |
| Color | White |
| Taste | Bitter and soapy (corrosive, not for tasting) |
| Polarity | Ionic |
| Type of Bond | Ionic (Na⁺ and OH⁻) |
Introduction to Sodium Hydroxide
Sodium hydroxide (NaOH), commonly called caustic soda or lye, is one of the most widely used industrial chemicals. It is a strong alkali that completely dissociates in water, producing hydroxide ions \(OH^-\) and making the solution highly basic. Sodium hydroxide appears as white, odorless flakes, pellets, or granules and is highly soluble in water, releasing significant heat during dissolution.
Because of its corrosive nature and strong reactivity, NaOH is employed in soap and detergent manufacturing, textile processing, petroleum refining, paper production, and chemical synthesis. It plays a vital role in neutralization reactions, acid-base titrations, and water treatment applications.
Structure and Bonding
The structure of sodium hydroxide is composed of ionic bonds between the sodium cation \(Na^+\) and the hydroxide anion \(OH^-\). In the solid state, NaOH forms a crystalline lattice stabilized by electrostatic attraction between positively and negatively charged ions. In aqueous solution, NaOH dissociates completely:
\(NaOH \rightarrow Na^+ + OH^-\)
The hydroxide ion is responsible for its strong alkalinity and ability to react vigorously with acids and amphoteric substances like aluminum and zinc. The ionic nature of NaOH makes it a good conductor of electricity in aqueous solutions, which is why it’s used in electrolysis processes.
Preparation of Sodium Hydroxide
Commercially, sodium hydroxide is prepared by the electrolysis of brine (aqueous sodium chloride solution) through the Chlor-Alkali Process. The reaction produces three important products: sodium hydroxide, chlorine gas, and hydrogen gas.
\(2NaCl + 2H_2O \xrightarrow{Electrolysis} 2NaOH + H_2 + Cl_2\)
During the process, brine is electrolyzed in a diaphragm, mercury, or membrane cell. The sodium ions migrate towards the cathode, where they combine with hydroxide ions formed from the reduction of water, producing NaOH. This process is central to the chemical industry due to the widespread applications of both sodium hydroxide and chlorine.
Physical and Chemical Properties
- Physical Appearance: White, crystalline, hygroscopic solid.
- Solubility: Highly soluble in water, ethanol, and methanol, producing a strongly exothermic dissolution.
- Reaction with Acids: Neutralizes acids to form salt and water (neutralization reaction).
- Reaction with Carbon Dioxide: Reacts with atmospheric CO₂ to form sodium carbonate.
- Reaction with Metals: Reacts with amphoteric metals like aluminum and zinc, releasing hydrogen gas.
\(NaOH + HCl \rightarrow NaCl + H_2O\)
\(2NaOH + CO_2 \rightarrow Na_2CO_3 + H_2O\)
\(2Al + 2NaOH + 6H_2O \rightarrow 2Na[Al(OH)_4] + 3H_2\)
Sodium hydroxide also absorbs moisture and carbon dioxide from the air, so it is stored in airtight containers.
Uses and Applications
- Soap and Detergent Industry: NaOH is a key ingredient in the saponification process, where fats or oils react with alkali to form soap and glycerol.
- Textile Industry: Used for mercerizing cotton, which enhances strength and luster of fabrics.
- Paper Industry: Involved in pulping and bleaching processes to remove lignin from wood.
- Petroleum Industry: Helps in refining petroleum products by neutralizing acidic impurities.
- Food Industry: Used for peeling fruits and vegetables, processing cocoa, and softening olives (under controlled conditions).
- Laboratory Applications: Commonly used in acid-base titrations and preparation of reagents.
- Water Treatment: Adjusts pH and removes heavy metal ions by precipitation.
\(Fat + NaOH \rightarrow Soap + Glycerol\)
Health and Safety Considerations
Sodium hydroxide is a highly corrosive and caustic substance. Direct contact with skin or eyes can cause severe burns and permanent damage. Inhalation of dust or mist can lead to respiratory irritation. It should be handled using protective gear such as gloves, goggles, and lab coats.
In case of contact, the affected area must be washed thoroughly with running water for at least 15 minutes. Sodium hydroxide should always be stored in tightly sealed, corrosion-resistant containers away from acids, organic compounds, and moisture to prevent hazardous reactions.
Despite its hazards, NaOH is safe when used responsibly under controlled conditions and remains indispensable in modern industry, chemistry, and environmental management.
Key Reactions of Sodium Hydroxide
Neutralization Reaction with Acids
As a strong base, sodium hydroxide reacts vigorously with acids to form salts and water. This type of reaction is exothermic:
\(NaOH + HCl \rightarrow NaCl + H_2O\)
This reaction forms the basis of acid-base titrations in laboratories and is fundamental to chemical manufacturing processes.
Reaction with Carbon Dioxide
Sodium hydroxide absorbs carbon dioxide from the air, forming sodium carbonate and water:
\(2NaOH + CO_2 \rightarrow Na_2CO_3 + H_2O\)
This reaction demonstrates NaOH's use as a CO₂ absorber in closed environments such as submarines and spacecraft.
Reaction with Aluminum
When sodium hydroxide reacts with aluminum in water, it forms sodium aluminate and releases hydrogen gas:
\(2Al + 2NaOH + 6H_2O \rightarrow 2Na[Al(OH)_4] + 3H_2\)
This reaction highlights NaOH’s ability to dissolve amphoteric metals and is used in aluminum processing industries.