Question

Arrange the following in order of increasing molar conductivity.

i) \[\ce{Mg[Cr(NH3) (Cl)5]}\]

ii) \[\ce{[Cr(NH3)5 Cl]3 [CoF6]2}\]

iii) \[\ce{[Cr(NH3)3 Cl3]}\]

Answer 1

These complexes can ionise in solution as:

i) \[\ce{Mg[Cr(NH3) (Cl)5] = Mg^2+ [Cr(NH3) (Cl)]^2-}\]

ii) \[\ce{[Cr(NH3)5 Cl]3 [CoF6]2 = [Cr(NH3)5Cl]^2+ + [CoF6]^3-}\]

iii) \[\ce{[Cr(NH3)3 Cl3]}\] = does not ionize

As the number of ions in the solution increases, their molar conductivity also increases.

Therefore, conductivity follows the order:

\[\ce{[Cr(NH3)3 Cl3] < [Cr(NH3)5Cl]3 [CoF6]2 < Mg[Cr(NH3)(Cl5)]}\]