Chemical Formula of Borax

Borax having formula Na2B4O7 and commonly known as sodium tetraborate decahydrate is the chemical of born and broadly uses in medicine, pest control like boric acid powder, and enamel preparation. Borax has ten units of hydrated water molecules and properties to the formation of the bead crystals structure with a definite chemical color test.

Na2B4O7, 10H2O
or Na2[B4O5(OH)4], 8H2O

Chemical Structure of Borax

Chemical formula, uses and bead test color of borax

It has two tetrahedral structure of BO4 and two planner structure of BO3 units. Each BO4 shares two oxygen with two BO3 and one oxygen with the second BO4. The fourth oxygen forms the chemical bond to the boron of BO4 unit and hydrogen.

The born in planner BO3 unit is SP2 hybridized but the tetrahedral BO4 unit is SP3 hybridized with an additional electron from sodium. These hybrid orbital overlap with suitable orbitals of oxygen.

Preparation of Na2B4O7

Boiling the mineral colemanite with Na2CO3 solution uses for the preparation of Na2B4O7. The produced CaCO3 filtered out and concentration filtrate deposits crystals of borax.

2CaO,3B2O3+2Na2CO3=Na2B4O7+2CaCO3+2NaBO2

Another liquor containing NaBO2 again converted to borax by passing CO2.

NaBO2 + CO2 = Na2B4O7 + Na2CO3

Borax also obtained by heating the boric acid solution with NaCO3 and specific heat. It can be crystalline by cooling the solution.

4H3BO3 + Na2CO3 → Na2B4O7 + 6H2O + CO2↑

Physical Properties of Borax

  1. The physical properties of borax and boric acid are very much similar and forming a crystalline solid with soluble in water mainly hot water.
  2. At normal temperature, it contains ten molecule crystal water but at 62oC it contains five molecule crystal water.

Chemical Properties of Borax

An aqueous solution shows alkaline properties due to hydrolysis to NaOH and H3BO3. Since boric acid is a weak acid and tritiated against a strong acid using methyl orange (pH scale 3.1 to 4.4)

Na2B4O7 +2HCl + 5H2O = 2NaCl + 4H3BO3

Color of Borax Bead Test

On heating borax first swells due to losing of hydrating water. Anhydrous borax on further heating produced metaborate and boron trioxide.

Na2B4O7, 10H2O → 2NaBO2 + B2O3 + 10H2O

But the fusion with metal oxides forms the bead of metal borates having characteristic glossy color. Thus this bead test formula uses for the quantitative chemical analysis of metals, known as the borax bead test.

  1. When borax fusion with metal salts heated in oxidizing flame forms ic-metaborate with a characteristic glossy color.
  2. But when fusion with metal salts heated in reducing flame forms us-metaborate with a characteristic glossy color.
Metal compound Color of the bead
Oxidizing flame Reducing flame
Copper Green, blue Dull red
Iron Yellow Dark green
Cobalt Dark blue Dark blue
Nickel Brown colorless
Chromium Green Green

Reaction with Copper Sulfate

CuSO4, 5H2O + Heat → CuSO4 + 5H2O

2CuSO4 → 2CuO + 2SO2 + O2

Fusion this metal oxide with the borax bead in an oxidizing flame forms blue cupric metaborate but in reducing flame forms dull red cuprous metaborate.

CuO + B2O3 → Cu(BO2)2
2Cu(BO2)2 + C → Cu2(BO2) + CO + B2O3

Uses of Borax Powder

  1. Na2B4O7 is extensively used in the manufacture of optical and hard glasses.
  2. Borax used as an antiseptic in medicine and manufacturing of enamel and pest control like boric acid.
  3. Due to the low solubility of calcium and magnesium borates, it used as a water softener.
  4. Borax powder uses for preparation of glaze to pottery, stiffening candle-wicks, and laundering.