Question

Which colored bead is formed in borax bead test to detect $C{u}^{2+}$?

• A. Blue bead
• B. Red bead
• C. Green bead
• D. Black bead

Answer 1

The correct option is A Blue bead

Borax on strong heating loses its water of crystallization and then shrinks forming a glassy bead of sodium metaborate $\left(NaB{O}_2\right)$ and boric anhydride $\left(B_2{O}_3\right)$ as shown in reaction given below:
$N{a}_2{B}_4{O}_7.10H_{2}O\to N{a}_2{B}_4{O}_7+10H_{2}O$
$N{a}_2{B}_4{O}_7\to 2NaB{O}_2+B_2{O}_3$
$CuO+B_2{O}_3\to Cu(B{O}_2{)}_2\text{blue bead}$
Hence, correct option is a.