JEE Main · 2022 · Shift-IImediumPB11-027

When borax is heated with CoO on a platinum loop, blue coloured bead formed is largely due to

p-Block Elements (Class 11) · Class 11 · JEE Main Previous Year Question

Question

When borax is heated with CoO on a platinum loop, blue coloured bead formed is largely due to

Options
  1. a

    B2O3\mathrm{B_2O_3}

  2. b

    Co(BO2)2\mathrm{Co(BO_2)_2}

  3. c

    CoB4O7\mathrm{CoB_4O_7}

  4. d

    Co[B4O5(OH)4]\mathrm{Co[B_4O_5(OH)_4]}

Correct Answerb

Co(BO2)2\mathrm{Co(BO_2)_2}

Detailed Solution

Strategy: Identify the colored compound formed during the borax bead test with Cobalt.

Step 1: Reaction in the bead On heating Borax, it forms a glassy bead of \ceNaBO2\ce{NaBO2} and \ceB2O3\ce{B2O3}. \ceNa2B4O7Δ2NaBO2+B2O3\ce{Na2B4O7 \xrightarrow{\Delta} 2NaBO_2 + B_2O_3} Step 2: Bead color for Cobalt Cobalt oxide (\ceCoO)(\ce{CoO}) reacts with boric anhydride (\ceB2O3)(\ce{B2O3}) to form a blue metaborate: \ceCoO+B2O3Co(BO2)2\ce{CoO + B2O3 \to Co(BO2)_2}

Answer: (Option) [b] \ceCo(BO2)2\boxed{\text{Answer: (Option) [b] $\ce{Co(BO2)_2}$}}

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