Question
Explain borax bead test.
✓
Answer
$i.$ Borax bead test is used to detect coloured transition metal ions.
$ii.$ On heating, borax loses water molecules and swells up. On further heating, it melts and forms a transparent liquid, which solidifies into a glass like material known as borax bead.
$iii.$ The borax bead consists of sodium metaborate and boric anhydride, which reacts with metals salts to form coloured bead.
e.g. When borax is heated in a Bunsen burner flame with $\ce{CoO}$ on a loop of platinum wire, a blue coloured $\ce{Co(BO_2)_2}$ bead is formed.
$\underset{\text { Cobalt oxide }}{ \ce{CoO} }+\underset{\begin{array}{c}\text { Boric } \\ \text { anhydride }\end{array}}{ \ce{B_2O_3}} \longrightarrow \underset{\begin{array}{c}\text { Cobalt } \\ \text { metaborate } \\ \text { (Blue bead) }\end{array}}{ \ce{Co} \left( \ce{BO} _2\right)_2}$
$ii.$ On heating, borax loses water molecules and swells up. On further heating, it melts and forms a transparent liquid, which solidifies into a glass like material known as borax bead.
$iii.$ The borax bead consists of sodium metaborate and boric anhydride, which reacts with metals salts to form coloured bead.
e.g. When borax is heated in a Bunsen burner flame with $\ce{CoO}$ on a loop of platinum wire, a blue coloured $\ce{Co(BO_2)_2}$ bead is formed.
$\underset{\text { Cobalt oxide }}{ \ce{CoO} }+\underset{\begin{array}{c}\text { Boric } \\ \text { anhydride }\end{array}}{ \ce{B_2O_3}} \longrightarrow \underset{\begin{array}{c}\text { Cobalt } \\ \text { metaborate } \\ \text { (Blue bead) }\end{array}}{ \ce{Co} \left( \ce{BO} _2\right)_2}$
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