When concentrated HCl is added to aqueous solution of CoCl _2, its colour changes from reddish pink to deep blue. Which complex ion gives blue colour in reaction?

JEE Main 2015 Chemistry question

When concentrated HCl is added to aqueous solution of , its colour changes from reddish pink to deep blue. Which complex ion gives blue colour in reaction?

(1)
(2)
(3)
(4)Correct

Answer: (4)

Solution

In dilute aqueous solution cobalt(II) exists as the octahedral hexaaqua ion , which is pink. Adding concentrated HCl floods the solution with chloride, and because is both bulkier and a weaker-field ligand than water, the complex rearranges to the

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Question ID VK-115368