Given that the following equilibria are simultaneously established in a single l

Question

Given that the following equilibria are simultaneously established in a single large test tube:

Ni2+ (aq) + 2 OH- (aq) = Ni(OH)2 (s) (green precipitate)

Ni2+ (aq) + 6 NH3 (aq) = Ni(NH3)6 2+ (aq) (blue solution)

A. How would each of the equilibrium be affected if NH3 were added to the test tube? Be sure to explain your answer in terms of shifting equilibria.

B. What happened to the precipitate? The solution?

C. How would each of the equilibria be affected if HCl (which reacts with NH3 and OH-) were added to the mixture? Be sure to explain your answer in terms of shifting equilibria

D. Explain what happened. What would you observe (color)?

Explanation / Answer

Ni2+ (aq) + 2 OH- (aq) = Ni(OH)2 (s) (green precipitate)

Ni2+ (aq) + 6 NH3 (aq) = Ni(NH3)6 2+ (aq) (blue solution)

A)

Nickel water complex is green while Ni-NH3 complex is blue.

If we add ammonia equilibrium system will shift in Forward direction (blue).

B)

Ni(OH)2(green) in precipitate reacted with NH3 to give Ni(NH3)6 2+, which is blue in color.

C)

If HCl is added to the above mixture, it will remove all NH3 bonded to Ni and equilibrium will shift backward direction.

D)

HCl removes NH3 and Ni(OH)2 forms again. Color of the solution is green again.

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