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Question: Answered & Verified by Expert
Assertion : Aq. solution of $\mathrm{CoCl}_2$ is pink in colour. It turns blue in presence of conc. $\mathrm{HCl}$. Reason : It is due to the formation of $\left[\mathrm{CoCl}_4\right]^{2-}$.
ChemistryCoordination CompoundsAIIMSAIIMS 2013
Options:
  • A If both assertion and reason are true and reason is the correct explanation of assertion.
  • B If both assertion and reason are true but reason is not the correct explanation of assertion.
  • C If assertion is true but reason is false.
  • D If both assertion and reason are false.
Solution:
1671 Upvotes Verified Answer
The correct answer is: If both assertion and reason are true and reason is the correct explanation of assertion.
$\left[\mathrm{Co}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}+4 \mathrm{Cl}^{-} \rightleftharpoons\left[\mathrm{CoCl}_4\right]^{2-}+6 \mathrm{H}_2 \mathrm{O}$
Pink
Blue
According to Le Chatelier's principle, on adding conc. $\mathrm{HCl}$, the equilibrium shifts in forward direction giving blue colour. And when this blue colour is diluted, equilibrium shifts in backward direction leading to pink colour.

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