Question

When concentrated hcl is added to an aqueous solution of cocl2, its colour changes from reddish pink to deep blue. Which complex ion gives blue colour in this reaction?

Answer 1

If an aqueous solution contains both cobalt(II) and chloride ions, the blue ion CoCl42- forms

Answer 2

When concentrated hcl is added to an aqueous solution of cocl2, its colour changes from reddish pink to deep blue. complex ion [cocl4]2-gives blue colour in this reaction.

Aqueous solution of cobalt hexa hydrate is pink in colour due to its octahedral geometry. When conc Hcl is added to it the geometry is changed to tetra chloro cobalt as it assumes tetrahedral geometry. For this tetrahedral geometry the colour is deep blue.