Borax is heated on a platinum loop with CoCO₃, forming a blue bead. On continued heating, the bead turns red. Which combination explains this?

Question

TestHub · Accepted Answer

Concept:

• Borax bead test redox chemistry

• Thermal transformations of cobalt oxides

• Coordination chemistry of boron

Solution:

• Blue bead → Co²⁺ in tetrahedral B₂O₃network

• Continued heating → partial oxidation/recoordination → red bead

• Involves both redox and coordination changes

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