Question

Cobalt (III) chloride forms several octahedral complexes with ammonia. Which of the following will not give a test for chloride ions with silver nitrate at ${{25}^{\circ }}C$?
(a)- $CoC{{l}_{3}}.5N{{H}_{3}}$
(b)- $CoC{{l}_{3}}.6N{{H}_{3}}$
(c)- $CoC{{l}_{3}}.3N{{H}_{3}}$
(d)- $CoC{{l}_{3}}.4N{{H}_{3}}$

Answer 1

If the compound is an octahedral complex then the central metal atom in the complex must be attached to 6 ligands by the coordinate bond. The ions outside the coordination bracket will take place in the reaction.

Complete answer:
In the coordination compound, we know that not all the ions or elements take place in the reaction, only the elements or ions that are outside the coordination bracket.
It is mentioned in the question that Cobalt (III) chloride forms several octahedral complexes with ammonia, which means that cobalt is the central metal atom, and ammonia and chloride ions are the ligands.
In $CoC{{l}_{3}}.5N{{H}_{3}}$, the central metal atom is cobalt and there are 5 ammonia ligands and 1 chloride ion in the coordination bracket. The remaining two chloride ions can take place in the reaction and form 2 moles of silver chloride when reacted with silver nitrate.
In $CoC{{l}_{3}}.6N{{H}_{3}}$, the central metal atom is cobalt and there are 6 ammonia ligands in the coordination bracket. The remaining three chloride ions can take place in the reaction and form 3 moles of silver chloride when reacted with silver nitrate.
In $CoC{{l}_{3}}.3N{{H}_{3}}$, the central metal atom is cobalt and there are 3 ammonia ligands and 3 chloride ion in the coordination bracket. There is no remaining ion in the complex to take place in a chemical reaction.
In $CoC{{l}_{3}}.4N{{H}_{3}}$, the central metal atom is cobalt and there are 4 ammonia ligands and 2 chloride ion in the coordination bracket. The remaining one chloride ions can take place in the reaction and form 1 mole of silver chloride when reacted with silver nitrate.

Therefore, the correct answer is an option (c)- $CoC{{l}_{3}}.3N{{H}_{3}}$.

Note:
If the compound is mentioned that it forms a square planar complex then the number of ligands must be 4 and if the compound is mentioned that it forms an octahedral complex then the number of ligands must be 6.