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In aqueous solution the Co 3 ion forms a complex with six 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.

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Answer:

Kf = [[Co(NH₃)₆]³⁺] / [Co³⁺] [NH₃]⁶

Last step: [Cu(NH₃)₅]³⁺ + NH₃(aq) ⇄ [Co(NH₃)₆]³⁺(aq)

Explanation:

When the Co³⁺ ion is in presence of ammonia molecules in an aqueous solution, the hexahydrated complex is formed, following the equilibriums:

Co³⁺(aq) + NH₃(aq) ⇄ [Co(NH₃)]³⁺(aq)               K₁

[Co(NH₃)]³⁺ + NH₃(aq) ⇄ [Co(NH₃)₂]³⁺(aq)         K₂

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

[Co(NH₃)₃]³⁺ + NH₃(aq) ⇄ [Co(NH₃)₄]³⁺(aq)        K₄

[Co(NH₃)₄]³⁺ + NH₃(aq) ⇄ [Co(NH₃)₅]³⁺(aq)        K₅

[Cu(NH₃)₅]³⁺ + NH₃(aq) ⇄ [Co(NH₃)₆]³⁺(aq)       K₆ → Last step

Global reaction:

Co³⁺(aq) + 6 NH₃(aq) ⇄ [Co(NH₃)₆]³⁺(aq)

Based in the global reaction, Kf is defined as:

Kf = [[Co(NH₃)₆]³⁺] / [Co³⁺] [NH₃]⁶

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