Final answer:
The dissociation constant (Kd) is the reciprocal of the formation constant (Kf) and for Co(NH3)6^2+ is calculated using the formula Kd = [Co^2+][6NH3] / [Co(NH3)6^2+]. This formula determines the ratio of the dissociated ions to the complex ion at equilibrium.
Step-by-step explanation:
The dissociation constant (Kd) for a complex ion is the reciprocal of the formation constant (Kf). The correct formula for calculating the dissociation constant using the formation constant of Co(NH₃)₆²⁺ is given by option (b), which is Kd = [Co²⁺][6NH₃] / [Co(NH₃)₆²⁺]. This means that the dissociation constant for any complex ion, such as Co(NH₃)₆²⁺, can be found by taking the inverse of the formation constant provided in a reference such as Appendix K or a similar source.
The formation constant is specific to the complex in question and can vary greatly between different complexes. To exemplify the use of the dissociation constant, when the complex ion is in equilibrium with its component ions, the equilibrium expression based on the dissociation constant Kd can help calculate the concentrations of the species involved at equilibrium. Therefore, when you are given the formation constant for a complex ion, you simply take its reciprocal to find the dissociation constant.