Question

If ${\text{AgN}}{{\text{O}}_{\text{3}}}$ solution is added in excess to 1 M solution of ${\text{CoC}}{{\text{l}}_{\text{3}}}{\text{.XN}}{{\text{H}}_{\text{3}}}$, one mole of ${\text{AgCl}}$ is formed. What is the value of x?

Answer 1

Hint: This question requires knowledge of coordination chemistry and the oxidation state of atoms. When one mole of silver nitrate reacts with one mole chloride, one mole silver chloride is formed. Only the chloride ions which are not in the complex will react. The total number of ligands in a complex is 6.

Complete Step by step Solution:
Silver nitrate solution reacts with chloride anions present in the medium to form a curdy white precipitate of silver chloride, ${\text{AgCl}}$. The oxidation state of the cobalt cation in the given complex can be either $\left( { + 2} \right)$ or $\left( { + 3} \right)$. If the oxidation state is $\left( { + 2} \right)$, then the number of ammonia ions required to satisfy the secondary sphere would be while one chloride anion would satisfy the secondary sphere. Hence under these conditions, the number of chloride anions satisfying the primary valence is two which reacts with silver nitrate to form two moles of silver chloride. Hence this is not possible.
If the value of ‘X’ is 4, then there will be two chloride anions satisfying the secondary valance while only one chloride anion will satisfy the primary valance. This chloride anion will further react with the silver nitrate solution to form the precipitate of silver chloride.

Hence, the correct answer of the value of x is four.

Notes: There are two valances of a metal ion, the primary valence and the secondary valence. The primary valence satisfies the cationic charge of the metal ion in the complex while the secondary valence is the extra number electrons that are donated by the ligands to satisfy the coordination sphere of the metal.