Question

In aqueous solution the Hg 2 ion forms a complex with four ammonia molecules. Write the formation constant expression for the equilibrium between the hydrated metal ion and the aqueous complex. Under that, write the balanced chemical equation for the first step in the formation of the complex.

Answer 1

Answer:

Kf = [[Hg(NH₃)₄]²⁺] / [Hg²⁺] [NH₃]⁴

Last step: [Hg(NH₃)₃]²⁺ + NH₃(aq) ⇄ [Hg(NH₃)₄]²⁺(aq)  

Explanation:

When the Hg²⁺ ion is in presence of ammonia molecules in an aqueous solution, the tetrahydrated complex is formed, following the equilibriums:

Hg²⁺(aq) + NH₃(aq) ⇄ [Hg(NH₃)]²⁺(aq)               K₁

[Hg(NH₃)]²⁺ + NH₃(aq) ⇄ [Hg(NH₃)₂]²⁺(aq)         K₂

[Hg(NH₃)₂]²⁺ + NH₃(aq) ⇄ [Hg(NH₃)₃]²⁺(aq)        K₃

[Hg(NH₃)₃]²⁺ + NH₃(aq) ⇄ [Hg(NH₃)₄]²⁺(aq)       K₄ → Last step.

Global reaction is:

Hg²⁺(aq) + 4 NH₃(aq) ⇄ [Hg(NH₃)₄]²⁺(aq)

And Kf is defined as:

Kf = [[Hg(NH₃)₄]²⁺] / [Hg²⁺] [NH₃]⁴