Borax is a sodium salt of tetraboric acid. It is obtained from colemanite ore by boiling its solution with sodium carbonate.
Borax is normally formulated as Na2B4O7.10H2O. But it contains, tetranuclear units [B4O5. (OH)4]2-. This form is known as prismatic form. Borax also exists two other forms namely, jeweller or octahderal borax (Na2B4O7.5H2O) and borax glass (Na2B4O7).
Borax is basic in nature and its solution in hot-water is alkaline as it dissociates into boric acid and sodium hydroxide.
Na2B4O7 + 7H2O → 4H3BO3 + 2NaOH
On heating it forms a transparent borax beads.
Borax reacts with acids to form sparingly soluble boric acid.
Na2B4O7 + 2HCl + 7H2O → 4H3BO3 + 2NaCl
Na2B4O7 + H2SO4 + 5H2O → 4H3BO3 + 2Na2SO4
When treated with ammonium chloride it forms boron nitride.
Na2B4O7 + 2NH4Cl → 2NaCl + 2BN + B2O3 + 4H2O
· Borax is used for the identification of coloured metal ions
· In the manufacture optical and borosilicate glass, enamels and glazes for pottery
· It is also used as a flux in metallurgy and also acts as a preservative
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