Chemical Formula of Borax Powder
Borax, powder wrote as sodium tetra-borate decahydrate having chemical formula Na2B4O7, 10H2O, or Na2[B4O5(OH)4], 8H2O widely uses in old civilization to prepare glazes and hard glasses. Borax is an important chemical compound of element boron isolated in the nineteenth century by Davy, Gay-Lussc and Thenard. Heating of borax crystals first swells due to losing the hydrated water. On further heating anhydrous borax gives meta-borate and boron trioxide and the physical properties are very similar to boric acid and obtained on heating boric acid solution with sodium carbonate. Borax is an important chemical structure of boron widely uses in pesticide or insecticide for pest control, antiseptics in medicine, cleaner solution or water softener, and enamel preparation.
Borax Crystal Structure
It has two tetrahedral units of BO4 and two planners units of BO3. Each BO4 structure shares two oxygen with two BO3 units and one oxygen with the second BO4 unit. The fourth oxygen bonding with BO4 unit of boron and hydrogen atom. Therefore, the 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 the oxygen atom.
Preparation of Sodium tetra-borate decahydrate
Boiling the mineral colemanite with an alkaline solution of sodium carbonate uses for the preparation of sodium tetra-borate decahydrate. The produced calcium carbonate filtered out and concentration filtrate deposits as the crystals of borax.
Another solution containing NaBO2 again uses for the conversation of borax by passing carbon dioxide.
NaBO2 + CO2 = Na2B4O7 + Na2CO3
Borax also obtained by heating the boric acid solution with sodium carbonate and heat. It can be crystalline by cooling the solution.
4H3BO3 + Na2CO3 → Na2B4O7 + 6H2O + CO2↑
Properties of Na2B4O7, 10H2O
- The base properties of boron compounds like borax and boric acid are very much similar and forming a crystalline solid with soluble in liquid mainly hot water.
- At normal temperature, the borax structure contains ten molecules of hydrated water but at 62°C, it contains five molecules of hydrating water.
Properties of Borax Solution
Na2B4O7 +2HCl + 5H2O = 2NaCl + 4H3BO3
Color of Borax Bead Test
When we heating borax first swells due to losing of hydrating water. 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.
- When fusion with metal salts heated in oxidation flame forms ic-metaborate with a characteristic glossy color.
- But when fusion with metal salts heated in reduction flame forms us-metaborate with a characteristic glossy color.
|Metal compound||Color of the bead|
|Oxidizing flame||Reducing flame|
|Copper||Green, blue||Dull red|
|Cobalt||Dark blue||Dark blue|
Borax Bead Test of Copper
CuSO4, 5H2O + Heat → CuSO4 + 5H2O
2CuSO4 → 2CuO + 2SO2 + O2
Fusion this metal oxide 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
- Sodium tetra-borate decahydrate is extensively used in the manufacture of optical and hard glasses.
- Borax used as a cleaner, antiseptic in medicine, and manufacturing of enamel and pest control like boric acid.
- Due to the low solubility of calcium and magnesium borates, borax used as a cleaner or water softener.
- Borax powder uses for preparation of glaze to pottery, stiffening candle-wicks, and laundering.