Select the correct increasing order of conductivity of the given complexes in their solution
(A) $[Co(NH_3)_6]Cl_3$
(B) $[Cr(NH_3)_5Cl] Cl_2$
(C) $[Co(NH_3)_4Cl_2] Cl$
(D) $[Co(NH_3)_3Cl_3]$
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (D), (C), (B), (A)
The electrical conductivity of coordination compounds in aqueous solution depends on the number of ions produced per formula unit (i.e., the degree of ionization). The complexes dissociate as follows:
- (D) [Co(NH₃)₃Cl₃]: Neutral complex (all Cl⁻ inside coordination sphere) → no ions → non-conducting.
- (C) [Co(NH₃)₄Cl₂]Cl: Dissociates into [Co(NH₃)₄Cl₂]⁺ + Cl⁻ → 2 ions → 1:1 electrolyte.
- (B) [Cr(NH₃)₅Cl]Cl₂: Dissociates into [Cr(NH₃)₅Cl]²⁺ + 2Cl⁻ → 3 ions → 1:2 electrolyte.
- (A) [Co(NH₃)₆]Cl₃: Dissociates into [Co(NH₃)₆]³⁺ + 3Cl⁻ → 4 ions → 1:3 electrolyte.
Increasing order of conductivity:
No ions < 2 ions < 3 ions < 4 ions → (D) < (C) < (B) < (A)
This is a standard concept in coordination chemistry (van’t Hoff factor and molar conductance increase with more ions). All these are +3 metal complexes with chloride ligands outside the sphere determining ionization.
Thus, the correct option is (D), (C), (B), (A).