BoraxSome p-Block ElementsNEET ChemistryNEET 2025Borax StructureBorax PropertiesBorax Bead Test
Borax Structure & Properties: NEET Cheat Sheet
Some p-Block Elements·2 min read·NEET 2026
What NEET Asks
Questions often focus on the correct structural formula of hydrated borax.
Reactions of borax upon heating and with acids are frequently tested.
Properties like the nature of its aqueous solution (alkaline) and the borax bead test are important.
Key Points
Borax, Na₂B₄O₇·10H₂O, is correctly formulated as Na₂[B₄O₅(OH)₄]·8H₂O, indicating 8 water molecules of crystallization and 2 coordinated as hydroxyl groups.
The anion [B₄O₅(OH)₄]²⁻ is a tetranuclear unit comprising two trigonal planar BO₃ units and two tetrahedral BO₄ units.
It contains four B-O-B bridging linkages.
Borax is a white crystalline solid, sparingly soluble in cold water but readily soluble in hot water.
Its aqueous solution is alkaline due to hydrolysis.
On heating, it loses water, swells, forms a transparent glassy bead (sodium metaborate and boric anhydride).
Students often use Na₂B₄O₇·10H₂O as the structural formula instead of Na₂[B₄O₅(OH)₄]·8H₂O, leading to incorrect calculations of B-O bonds or coordination numbers.
Don't confuse the anhydrous borax (Na₂B₄O₇) with the glassy mixture (NaBO₂ + B₂O₃) formed on strong heating.
Misinterpreting the alkaline nature of borax solution, forgetting it's due to the strong base (NaOH) formed upon hydrolysis.
Rapid Revision
Remember borax is Na₂[B₄O₅(OH)₄]·8H₂O with 2 trigonal and 2 tetrahedral boron atoms. Its aqueous solution is alkaline due to hydrolysis. Strong heating yields a glassy mixture of sodium metaborate and boric anhydride, crucial for the borax bead test.
Frequently Asked Questions
What is the correct structural formula of borax?▾
The correct structural formula for hydrated borax is `Na₂[B₄O₅(OH)₄]·8H₂O`. It shows that 8 water molecules are molecules of crystallization, and 2 H₂O molecules are involved in forming hydroxyl groups on the boron atoms within the anion.
Why is borax solution alkaline in water?▾
Borax solution is alkaline because when it dissolves in water, it undergoes hydrolysis. It reacts with water to form a strong base, sodium hydroxide (NaOH), and a weak acid, orthoboric acid (H₃BO₃). The presence of the strong base makes the solution alkaline.
What happens when borax is strongly heated?▾
Upon strong heating, borax first loses its water of crystallization and swells up. Further heating converts it into a transparent glassy bead, which is a mixture of sodium metaborate (NaBO₂) and boric anhydride (B₂O₃). This glassy bead is used in the borax bead test.
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