In the borax bead test, which compound is formed?

In the borax bead test, which compound is formed?
  1. Orthoborate
  2. Metaborate
  3. Double oxide
  4. Tetraborate

Solution

In borax bead test the coloured Metaborates are formed by transition metal salts. $\begin{aligned} \mathrm{Na}_2 \mathrm{~B}_4 \mathrm{O}_7 \stackrel{\Delta}{\longrightarrow} & 2 \mathrm{NaBO}_2+\mathrm{B}_2 \mathrm{O}_3 \\ \text { Salt of } \mathrm{Co} \stackrel{\Delta}{\longrightarrow} & \mathrm{CoO}+\text { gas } \\ \mathrm{CoO}+\mathrm{B}_2 \mathrm{O}_3 \stackrel{\Delta}{\longrightarrow} & \mathrm{Co}\left(\mathrm{BO}_2\right)_2 \\ & \begin{array}{c} \text { cobalt metaborate } \\ \text { (blue colour) } \end{array} \end{aligned}$

Asked in: NEET 2002

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