For the reaction given below : CoCl_3 . x NH_3 + AgNO_3 (aq) \to If two equivalents of AgCl precipitate out, then the value of x will be \underline\hspace2cm .

D and F Block Elements PYQ — JEE Main 2022 · 29 Jun · Shift 2 · Q20 with Solution

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Correct answer: 5

We are given a cobalt(III) ammine chloride complex of the form $CoCl_3\cdot xNH_3$ and it is treated with aqueous $AgNO_3$ .
$AgNO_3$ precipitates only those chloride ions which are present as ionisable chloride ions outside the coordination sphere: $Ag^+ + Cl^- \to AgCl\downarrow$
Since two equivalents of $AgCl$ are obtained, there must be two chloride ions outside the coordination sphere.
Total number of chloride ions in $CoCl_3\cdot xNH_3$ is 3.
If 2 are outside, then 1 chloride ion must be inside the coordination sphere.
Cobalt(III) generally has coordination number 6 in such ammine complexes. So the coordination sphere must contain:
- 1 coordinated $Cl^-$
- $x$ coordinated $NH_3$
Therefore, $x + 1 = 6$
Solving: $x = 5$
Hence the complex is: $[Co(NH_3)_5Cl]Cl_2$ which indeed gives 2 moles of $AgCl$ with $AgNO_3$ .

Therefore, the required value is: $\boxed{5}$