JEE Main · 2023 · 29 Jan 2023 · Shift 1 · p-Block Elements

During the borax bead test with

CuSO_{4}

, a blue green colour of the bead was observed in oxidising flame due to the formation of

(A) $Cu_{3} B_{2}$
(B)Cu
(C) $Cu (BO_{2})_{2}$ ✓ Correct
(D)CuO

Answer: (C)

Solution

In the borax bead test the borax fuses to a clear glass of sodium metaborate and boric anhydride. A trace of copper sulphate on heating loses

S O_{3}

to give cupric oxide, which dissolves in the hot bead and combines with boric anhydride,

CuO + B_{2} O_{3} \to Cu (B O_{2})_{2}

. The blue-green colour seen in the oxidising flame is due to this copper metaborate,

Cu (B O_{2})_{2}

JEE Main · 2023 · 29 Jan 2023 · Shift 1 · Single correct option

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