Question

The conductivity of a solution of complex with formula CoCl₃(NH₃)₄ corresponds to 1 : 1 electrolyte, then the primary valency of central metal ion is ______.

Answer 1

Correct Answer: 3

To determine the primary valency of the central metal ion in the complex CoCl₃(NH₃)₄ that behaves as a 1:1 electrolyte, we first need to explore the possible dissociation of the complex in solution. The conductivity data suggests the formation of one positive central metal ion and one negatively charged complex ion. Therefore, the complex is likely to dissociate as:

CoCl₃(NH₃)₄ → [Co(NH₃)₄Cl]⁺ + 2Cl^-

This indicates there are 2 chloride ions acting as counter ions outside the coordination sphere. This behavior matches that of a 1:1 electrolyte as only one ion contributes to the overall conductivity apart from the complex.

The primary valency (oxidation state) of cobalt in the complex can be calculated as:

• Let the oxidation state of Co be x.
• Each NH₃ ligand is neutral.
• Each chloride ion (Cl^-) contributes a charge of -1.

The charge balance equation based on the species generated is:

x + 0(NH₃) - 2(Cl^-) = +1 (due to the overall charge of the complex ion [Co(NH₃)₄Cl]⁺)

Solving for x gives: x - 2 = +1, hence x = +3.

Therefore, the primary valency of the central metal ion, cobalt, is 3.

Checking against the provided range (3,3), we confirm the computed value of 3 is indeed within the specified range.