JEE Main 2015 · 11 Apr · Shift 1 · Chemistry Q48

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ChemistrySingle correct+4 / -1Question 48 of 90

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

\ce{[CoCl6]^4-}

\ce{[CoCl6]^3-}

\ce{[CoCl4]^2-}

\ce{[Co(H2O)6]^2+}

Answer and worked solution

Official answer: C

Excess $\ce{Cl-}$ converts pink octahedral $\ce{[Co(H2O)6]^2+}$ into blue tetrahedral $\ce{[CoCl4]^2-}$ .

Topics:Magnetic properties and colour Crystal field theory

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JEE Main 2015 · 11 Apr · Shift 1, Chemistry question 48