Assertion : Coloured cations can be identifie | vedclass

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Question

Borax $(Na_2B_4O_7)$ when heated at about $740\,^oC$, forms a glassy bead which gives
different colour beads with different cations. Hence, it is use

Vedclass · Accepted Answer

If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

Vedclass · Answer

Borax $(Na_2B_4O_7)$ when heated at about $740\,^oC$, forms a glassy bead which gives
different colour beads with different cations. Hence, it is used to identify cations in qualitative analysis. This test is called borax bead test.

$N{{a}_{2}}{{B}_{4}}{{O}_{7}}\,\xrightarrow{740\,{{\,}^{o}}C}\underbrace{\underset{\begin{smallmatrix} 
 \,\,\,	ext{sodium } \ 
 	ext{metaborate} 
\end{smallmatrix}}{\mathop{2NaB{{O}_{2}}}}\,\,+\,\,\underset{\begin{smallmatrix} 
 	ext{ boric} \ 
 anhydride 
\end{smallmatrix}}{\mathop{{{B}_{2}}{{O}_{3}}}}\,}_{	ext{glassy bead}}$

Assertion : Coloured cations can be identified by borax bead test.

Reason : Transparent bead $(NaBO_2 + B_2O_3)$ forms coloured bead with coloured cation.

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