devarshi-dt-logo

Question:

When concentrated HCl is added to an aqueous solution of CoCl2, its color changes from reddish pink to deep blue. Which complex ion gives color in this reaction?

[CoCl6]3−

[CoCl4]2−

[CoCl6]4−

[Co(H2O)6]2+

Solution:

When concentrated HCl is added to an aqueous solution of CoCl2, its color changes from reddish pink to deep blue. Co(II) is oxidized to Co(III). This indicates the formation of [CoCl4]2−. CoCl2 + HCl → [CoCl4]2−.