Borax

Borax, also known as sodium borate, sodium tetraborate, or disodium tetraborate decahydrate, is a naturally occurring mineral and an important boron compound with the chemical formula Na₂B₄O₇·10H₂O. It has been used for centuries in a variety of applications ranging from household cleaning and glassmaking to metallurgy, agriculture, and medicine. In modern chemistry and industry, borax serves as a versatile compound due to its cleansing, buffering, antiseptic, and fluxing properties.

Occurrence and Natural Sources

Borax occurs naturally as evaporite deposits in arid regions where seasonal lakes repeatedly evaporate, leaving behind borate minerals. It is commonly found in:

• Dry lake beds and salt flats in regions such as California (notably in Death Valley), Turkey, Tibet, and Chile.
• Mineral form, borax appears as soft, colourless or white crystalline deposits, often with a pearly lustre.

The most important commercial source of borax is the mineral tincal, a hydrated form of sodium borate. It is mined, refined, and crystallised for use in various industries.

Chemical Composition and Structure

• Chemical formula: Na₂B₄O₇·10H₂O
• Molecular weight: 381.37 g/mol
• Appearance: White crystalline solid
• Solubility: Soluble in water; insoluble in alcohol
• Melting point: Around 75°C (loses water of crystallisation on heating)

When heated, borax loses its water molecules and forms anhydrous sodium tetraborate (Na₂B₄O₇), which is used in glass and ceramic manufacturing.
Thermal decomposition:
Na₂B₄O₇\cdotp10H₂O → Na₂B₄O₇ + 10H₂O↑\text{Na₂B₄O₇·10H₂O → Na₂B₄O₇ + 10H₂O↑}Na₂B₄O₇\cdotp10H₂O → Na₂B₄O₇ + 10H₂O↑
When further heated, the anhydrous salt fuses into a glassy substance called borax bead, used in qualitative inorganic analysis for detecting metal ions.

Historical Background

Borax has been known since ancient times. It was traded along the Silk Route from Tibet to the Middle East and Europe. Ancient Egyptians used it in the mummification process, as a flux for goldsmithing, and as a cleaning agent. In the 19th century, it gained prominence due to its use in metallurgy and glassmaking, particularly through large-scale mining in California’s Death Valley and Nevada.

Preparation and Manufacture

Commercially, borax is produced from boron-containing minerals and solutions through the following steps:

1. Extraction: Borate ores such as tincal (Na₂B₄O₇·10H₂O) or kernite (Na₂B₄O₇·4H₂O) are mined.
2. Dissolution: The ore is dissolved in hot water to form a borate solution.
3. Crystallisation: On cooling, borax crystallises as Na₂B₄O₇·10H₂O.
4. Purification: The crystals are filtered, washed, and dried for commercial use.

Chemical Properties

Borax exhibits several useful chemical behaviours:

• Alkalinity: It has mild basic properties (pH ≈ 9.3 in aqueous solution).
• Hydrolysis: In water, borax partially hydrolyses to form boric acid and sodium hydroxide.

  Na2B4O7+7H2O→4H3BO3+2NaOHNa₂B₄O₇ + 7H₂O → 4H₃BO₃ + 2NaOHNa2​B4​O7​+7H2​O→4H3​BO3​+2NaOH

• Buffering Action: It acts as a buffer solution with boric acid, maintaining stable pH in chemical and biological systems.
• Glass Formation: On heating with metal oxides, it forms borates that dissolve metal impurities, a property used in fluxing.

Uses and Applications

Borax has a wide range of applications across industries, domestic life, and laboratories:
1. Household and Cleaning Uses:

• Serves as a natural cleaner, deodoriser, and laundry booster.
• Used in detergents and soaps to soften hard water and enhance cleansing efficiency.
• Effective for removing stains, mould, and mildew due to its mild alkalinity.

2. Industrial Uses:

• Glass and Ceramics: Acts as a flux to lower the melting point of silica, improving the transparency and strength of glass. Essential in borosilicate glass production.
• Metallurgy: Used as a fluxing agent in soldering, welding, and refining precious metals such as gold and silver.
• Textiles and Paper: Functions as a pH stabiliser and flame retardant.
• Chemical Manufacturing: Used in the production of boric acid, enamels, fertilisers, and cosmetics.

3. Laboratory Applications:

• Employed in the borax bead test to detect metal cations. When heated with metal oxides, borax forms coloured glassy beads, each colour characteristic of the metal present.
  • Example: Cobalt → Blue bead, Chromium → Green bead, Iron → Yellowish brown bead.
• Acts as a buffering agent in biochemical experiments.

4. Agricultural Uses:

• Provides boron micronutrients to plants, essential for cell wall formation and reproductive development.
• Used in small quantities as fertiliser additives to correct boron deficiency in soils.

5. Medical and Cosmetic Uses:

• Traditionally used as an antiseptic and anti-fungal agent in lotions and mouthwashes (though largely replaced by safer compounds today).
• A component in some toothpastes, skincare products, and eye washes due to its mild disinfectant properties.

6. Polymer and Slime Production:

• In chemistry education, borax is a key ingredient in making polymer slime, where it reacts with polyvinyl alcohol (PVA) to form cross-linked, elastic gels.

Environmental and Safety Aspects

Although borax is a naturally occurring mineral, it should be handled with care:

• Health Hazards: Prolonged exposure or ingestion may cause irritation to skin, eyes, or respiratory tract. It can be toxic in large doses.
• Environmental Impact: Boron compounds can accumulate in soil and water, potentially affecting plant and aquatic life if used excessively.
• Regulation: In some countries, borax is regulated as a potentially hazardous substance in household and cosmetic products.

Safe handling involves using gloves, eye protection, and avoiding direct inhalation or ingestion.

Related Compounds

Borax belongs to the family of borates, which includes related compounds such as:

• Boric Acid (H₃BO₃): Used as an antiseptic, insecticide, and flame retardant.
• Kernite (Na₂B₄O₇·4H₂O): Another natural source of boron.
• Colemanite (Ca₂B₆O₁₁·5H₂O): Used in glass and ceramic industries.

Historical and Economic Importance

Borax played a major role in the expansion of the chemical and glass industries during the 19th and 20th centuries. The “20 Mule Team Borax” of Death Valley, California, became a famous symbol of American industrial development. Today, borax remains a cornerstone in boron mining economies such as Turkey and the United States.