Question

Colourless salt $\left(X\right)\underset{}{\overset{\Delta }{\to }}\left(Y\right)\underset{}{\overset{{Cu}^{2+}/\Delta }{\to }}$ coloured bead $\left(Z\right)$. $\left(X\right)$ can be:

• A. borax
• B. microcosmic salt
• C. both $A$ and $B$
• D. none of these

Answer 1

Answer: (C)

both $A$ and $B$

In oxidising flame, copper forms copper meta borate which is blue in colour.
$N{a}_2{B}_4{O}_7+CuS{O}_4\to 2NaB{O}_2+Cu(B{O}_2{)}_2+S{O}_3$
(Blue)
While in a reducing flame, copper meta borate is reduced to metallic copper, which is red and opaque.
$2Cu(B{O}_2{)}_3+4NaB{O}_2+2C\underset{}{\overset{\Delta }{\to }}2Cu+2N{a}_2{B}_4{O}_7+2CO$
(Red opaque)
$B_2{O}_3+CuS{O}_4\to Cu(B{O}_2{)}_2+S{O}_3$
(Blue)
$\left(X\right)$ can be borax or microcosmic salt.