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An aqueous pink solution of cobalt(II) chloride changes to deep blue on the addition of an excess of HCl. This is because____________.

(i) [Co(H_{2}O)_{6}]^{2+} is transformed into [CoCl_{6}]^{4-}

(ii) [Co(H_{2}O)_{6}]^{2+} is transformed into [CoCl_{4}]^{2-}

(iii) tetrahedral complexes have smaller crystal field splitting than octahedral complexes.

(iv) tetrahedral complexes have larger crystal field splitting than octahedral complex.

Answers (1)

Option (ii) and (iii) are the correct answers.

Explanation: The transition of electrons from t2g to eg energy level gives an aqueous pink solution of cobalt (II) chloride in [Co(H_{2}O)_{6}]^{2+} complex and when excess HCl is added to the solution:

(i) [Co(H_{2}O)_{6}]^{2+} is transformed into [CoCl_{4}]^{2-}

(ii) Tetrahedral complexes have smaller crystal field splitting than octahedral complexes because \Delta _{r}=\frac{4}{9}\Delta _{0}

Hence, options (b) and (c) are correct.

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