[B4O5(OH)4]2− anion structure in borax.
Generally borax is described as Na2B4O7·10H2O, it contains [B4O5(OH)4]2− units so it is for the better formulated as Na2[B4O5(OH)4]·8H2O. In this structure, there are two sp2 hybridised boron atoms with triangular geometry and two boron atoms in tetrahedral geometry (sp3 hybridisation), with each carrying a formal charge of −1.
Borax (sodium borate) is a white crystalline solid, that occurs naturally as Tincal. It is a sodium salt of weak boric acid with general formula Na2B4O7.10H2O (IUPAC name Sodium tetraborate decahydrate). Borax is commonly used in laundry detergents and as an insecticide.
Preparation of Borax:
From Tincal: Tincal present in dried up lakes is taken out and boiled with water. The solution is filtered to remove insoluble impurities and then concentrated followed by cooling to get crystals of borax.
From mineral Colemanite: Fine powdered colemanite (Ca2B6O11) is boiled with washing soda solution (Sodium carbonate)
The solution is filtered to remove the precipitated calcium carbonate. It is then concentrated and cooled to get the crystals of borax. The mother liquor containing sodium metaborate is treated with current of CO2 gas which converts it into borax.
Pure Borax powder
From boric acid: In small amounts, borax can also be prepared from boric acid by neutralising with sodium carbonate. Upon concentrating and cooling the solution, crystals of borax (Na2B4O7.10H2O) separate out.
Borax bead test for the qualitative identification of many metals that produce characteristic colors
Properties:
It is a white crystalline solid, less soluble in cold water but more soluble in hot water.
Borax dissolves in water to give an alkaline solution.
Borax on prolonged heating forms a transparent liquid, which solidifies into glass like material known as borax bead which consists of sodium metaborate and boric anhydride.
The borax beads are used in laboratory to identify some metals in salts, through borax bead test. Nickel salts give brown colored bead, cobalt gives blue colored bead, while chromium salt gives green bead in flame with borax bead.
Borax in ceramics manufacture
Uses of borax:
- Used in manufacture of fused products such as glass, ceramics and enamel glazes.
- Used as flux for soldering.
- Used in manufacture of drugs, cosmetics and laundry detergents.
- Used as antiseptic soaps.
- Used in fertilizers as micronutrients
- Used in chemical laboratories to make buffers.
- It is also used as fungicide, fire retardant and in softening water.