Silica gel contains [ CoCl 4 ] 2 − as an indicator. When activated, silica gel becomes dark blue while upon absorption of moisture, its colour changes to pale pink. This is because :

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Silica gel contains [ CoCl 4 ​ ] 2 − as an indicator. When activated, silica gel becomes dark blue while upon absorption of moisture, its colour changes to pale pink. This is because :

TestHub · Accepted Answer

The dark blue [ CoCl 4 ​ ] 2 − complex is tetrahedral. Upon absorbing moisture, water ligands replace chloride, forming the pale pink [ Co ( H 2 ​ O ) 6 ​ ] 2 + complex. This changes the coordination number of Co(II) from 4 to 6, altering the crystal field splitting and thus the color.

Chemistry - Coordination Chemistry Question with Solution | TestHub

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