Subject: Inorganic Chemistry · Chapter: Coordination Chemistry · Topic: Crystal Field Theory · Exam: CSIR-NET 2013 · Marks: 2 · Difficulty: Medium
Silica gel contains $\left[\mathrm{Co}\left(\mathrm{Cl}_{4}\right)\right]^{2-}$ as an indicator. When activated, silica gel becomes dark blue while upon absorption of moisture, its colour changes to pale pink This is because,
(a)Co (II) changes its coordination from tetrahedral to octahedral.
(b)Co (II) changes its oxidation state to Co(III)
(c)Tetrahedral crystal field splitting is NOT equal to octahedral crystal field splitting
(d)Co(II) forms kinetically labile while Co(III) forms kinetically inert complexes.