Sodium borate - Na2[B4O5(OH)4].8H2O

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What is Sodium borate?

Na2[B4O5(OH)4]·8H2O is an important boron compound and a salt of boric acid with the chemical name Sodium borate. It is also called Borax or Disodium tetraborate, or Sodium tetraborate. It was first discovered in the 8th century AD in the dry lake beds in Tibet. It was imported through the Silk Road to the Arabian Peninsula.

Borax in its powder is soft colourless to white coloured crystals. It is completely soluble in water and ethylene glycol. It moderately dissolves in methanol, and diethylene glycol and is slightly soluble in acetone. As temperature increases, its solubility in water increases significantly. It is mostly used as a component in detergents, enamel glazes, and cosmetics. It is widely used in making buffer solutions, as an antifungal compound, as a fire retardant, as a flux in metallurgy, as a texturing agent in cooking, and as an insecticide.

Properties of Sodium borate – Na2[B4O5(OH)4]·8H2O

Na2[B4O5(OH)4]·8H2O Sodium borate
Molecular weight of Na2[B4O5(OH)4]·8H2O 201.22 g/mol (anhydrate)
Density of Sodium borate 1.73 g/dm3
Boiling point of Sodium borate 1,575 °C
Melting Point of Sodium borate 743 °C

Structure of Sodium Borate
Sodium borate structure

Na2[B4O5(OH)4]·8H2O Uses (Sodium borate)

        • Sodium borate is used in food industry as a food additive.
        • Used as a fire retardant.
        • Used to prevent wood rot in boats.
        • Used as a curing agent for snake skins.
        • Used in swimming pools to control the pH.
        • Used as an ingredient in vitamin supplements.
        • Used in laundry cleaning products.
        • Used in household cleaning products.
        • Used in borax method.
        • Used in forge welding by blacksmiths.

Sodium borate Reactions

Sodium tetraborate can be converted to boric acid by reacting with hydrochloric acid(HCl). The reaction is as follows:

Na2B4O7·10H2O + 2 HCl → 4 B(OH)3 + 2 NaCl + 5 H2O

The decahydrate obtained is sufficiently stable and is used as a standard for acid base titrimetry.

When Sodium borate is added to a flame, it gives off a yellow green colour. Due to this reason it is not used in fireworks as it liberates yellow coloured sodium.

Health hazards

Over-exposure to borax dust causes respiratory irritation. Swallowing may cause gastrointestinal distress which includes nausea, diarrhoea, abdominal pain, and persistent vomiting. When it affects the human brain and vascular system it results in dullness and headache. Overexposure to boric acid also causes developmental and reproductive health issues.

Learn more about the Structure, physical and chemical properties of Na2[B4O5(OH)4]·8H2O from the experts at BYJU’S.

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