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 conductivity of a solution of a complex depends on the number of ions it gives. Ligands inside the coordination sphere stay bound to the metal; only the counter ions outside the square brackets are set free:
(A) \( \ce{[Co(NH3)6]Cl3 -> [Co(NH3)6]^3+ + 3Cl-} \): 1 + 3 = 4 ions.
(B) \( \ce{[Cr(NH3)5Cl]Cl2 -> [Cr(NH3)5Cl]^2+ + 2Cl-} \): 1 + 2 = 3 ions.
(C) \( \ce{[Co(NH3)4Cl2]Cl -> [Co(NH3)4Cl2]+ + Cl-} \): 1 + 1 = 2 ions.
(D) \( \ce{[Co(NH3)3Cl3]} \): all three chlorides are inside the coordination sphere; it does not ionise, 0 ions (non-electrolyte).
In increasing order of conductivity:
\( \displaystyle \ce{[Co(NH3)3Cl3]} \lt \ce{[Co(NH3)4Cl2]Cl} \lt \ce{[Cr(NH3)5Cl]Cl2} \lt \ce{[Co(NH3)6]Cl3} \)
Shortcut: The non-electrolyte (D) must come first; only Option (3) starts with (D).