Arrange the following complexes in order of their decreasing conductivity values?
A. [CoCl2(NH3)4]Cl
B. [CoCl(NH3)5]Cl2
C. [Co(NH3)6]Cl3
D. [CoCl3(NH3)3]
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → C, B, A, D
The molar conductivity of a complex salt depends on the number of ions it gives in solution. In a complex, the ligands inside the square bracket stay bound to the metal; only the ions outside the bracket are released.
Each of these complexes has cobalt(III) with coordination number 6. The more \( \ce{Cl^{-}} \) ions sit inside the bracket as ligands, the fewer are free:
(C) \( \ce{[Co(NH3)6]Cl3} \): gives \( \ce{[Co(NH3)6]^{3+}} \) + \( \ce{3Cl^{-}} \) = 4 ions
(B) \( \ce{[CoCl(NH3)5]Cl2} \): gives \( \ce{[CoCl(NH3)5]^{2+}} \) + \( \ce{2Cl^{-}} \) = 3 ions
(A) \( \ce{[CoCl2(NH3)4]Cl} \): gives \( \ce{[CoCl2(NH3)4]^{+}} \) + \( \ce{Cl^{-}} \) = 2 ions
(D) \( \ce{[CoCl3(NH3)3]} \): a neutral molecule, no ions, practically non-conducting
Shortcut: The neutral complex D must come last and the complex with no chloride ligand, C, first. Only Option (3) starts with C and ends with D.