A) metal borates
B) metal metaborates
C) metal phosphates
D) metal tetraborates
Correct Answer: B
Solution :
Borax is widely used in qualitative analysis, since it gives coloured beads with transition metal salts. The chemistry of the borax bead test is as follows : \[N{{a}_{2}}{{B}_{4}}{{O}_{7}}.10{{H}_{2}}O\xrightarrow{Heat}\] \[N{{a}_{2}}{{B}_{4}}{{O}_{7}}+10{{H}_{2}}O\] \[N{{a}_{2}}{{B}_{4}}{{O}_{7}}\xrightarrow{{{740}^{o}}}\underset{\underbrace{\text{sod}\text{.}\,\text{metaborate}\,\text{boric}\,\text{anhydride}}_{\text{Glassy}\,\text{bead}}}{\mathop{2NaB{{O}_{2}}+{{B}_{2}}{{O}_{3}}}}\,\] \[CuS{{O}_{4}}+{{B}_{2}}{{O}_{3}}\xrightarrow{{}}\underset{\text{copper}\,\text{metaborate}}{\mathop{CuO.{{B}_{2}}{{O}_{3}}}}\,+S{{O}_{3}}\] Thus coloured beads are formed due to the formation of metal metaborates.
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