Coordination Compounds 2 Question 50
####52. Addition of excess aqueous ammonia to a pink coloured aqueous solution of $M Cl _2 \cdot 6 H _2 O(X)$ and $NH _4 Cl$ gives an octahedral complex $Y$ in the presence of air. In aqueous solution, complex $Y$ behaves as $1: 3$ electrolyte. The reaction of $X$ with excess $HCl$ at room temperature results in the formation of a blue colured complex $Z$. The calculated spin only magnetic moment of $X$ and $Z$ is 3.87 B.M., whersas it is zero for complex $Y$.
Among the following options, which statement(s) is (are) correct?
(2017 Adv.)
(a) The hybridisation of the central metal ion in $Y$ is $d^{2} s p^{3}$
(b) Addition of silver nitrate to $Y$ given only two equivalents of silver chloride
(c) When $X$ and $Y$ are in equilibrium at $0^{\circ} C$, the colour of the solution is pink
(d) $Z$ is a tetrahedral complex
Assertion and Reason
Read the following questions and answer as per the direction given below:
(a) Statement I is true; Statement II is true; Statement II is the correct explanation of Statement I.
(b) Statement I is true; Statement II is true; Statement II is not the correct explanation of Statement I.
(c) Statement I is true; Statement II is false.
(d) Statement I is false; Statement II is true.
Show Answer
Answer:
Correct Answer: 52. (c)
Solution:
- $\left.\left.\underset{\text { Pink }(X)}{\left[Co\left(H _2 O\right) _6\right.}\right] _{Cl _2} \xrightarrow[O _2 \text { (Air) }]{\text { Excess } NH _4 OH / NH _4 Cl} \underset{Y}{Co\left(NH _3\right) _6}\right] Cl _3$
$$ \underset{X}{\left[Co\left(H _2 O\right) _6\right]^{2+}}+\underset{\text { (Excess) }}{4 Cl^{-}} \longrightarrow \underset{\text { blue Z }}{\left[CoCl _4\right]^{2-}} $$
(a) Since $NH _3$ is moderately strong ligand, hybridisation of cobalt in $Y$ is $d^{2} s p^{3}$.
(b) Cobalt is $s p^{3}$-hybridised in $\left[CoCl _4\right]^{2-}$.
(c) $\left[Co\left(NH _3\right) _6\right] Cl _3+3 AgNO _3($ aq $) \longrightarrow 3 AgCl \downarrow$
(d) $\left.\left[CoCl _4\right]^{2-}+6 H _2 O \rightleftharpoons \underset{\text { Blue }}{\left[Co\left(H _2 O\right) _6\right.}\right]^{2+}+4 Cl^{-} ; \Delta H<0$
