Question

Assertion: On cooling in a freezing mixture, colour of the mixture turns to pink from deep blue for a reaction.
$CO\left(H_{2}O{)}_6{}^{2+}\right(aq)+4C{l}^{⊝}(aq)\rightleftharpoons CoC{l}_4{}^{2-}(aq)+6H_{2}O(l)$
(Pink) (Blue)
Reason: The reaction is endothermic in forward reaction, so on cooling the reaction, deep blue colour appears.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct
• E. Both Assertion and Reason are incorrect

Answer 1

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

The reaction $\left[Co\right(H_{2}O{)}_6{]}^{2+}\left(aq\right)+4C{l}^{–}\left(aq\right)\rightleftharpoons \left[CoC{l}_4{]}^{2–}\right(aq)+6H_{2}O(l)$ is endothermic. The shift of octahedral to tetrahedral coordination cause the colour change from pink to blue color that occurs when the second chloride ion enters the coordination sphere. Therefore, in accordance with Le Chatelier’s principle, when the temperature is raised, the position of the equilibrium will move to the right, forming more of the blue complex ion at the expense of the pink species. And when mixture freezes it supports backward reaction forming more pink complex.