The tetramminecopper(ii) ion, cu(nh3)4 2+, has a formation constant kf = 1.1 x 10^13. what is the minimum concentration of free ammonia in solution required to ensure that at least 99.9% of the dissolved copper(ii) ion is found in the form of its ammonia complex? (a) 9 x 10^–14 m (b) 9 x 10^–11 m (c) 8 x 10^–4 m (d) 3 x 10^–3 m.

the answer is d. show how you get to the solution

The correct answer is option D, that is, 3 × 10⁻³ M.  

The following is the equation that represent the equilibrium for the formation of tetramminecopper (II) ion:  

Kf = [Cu(NH₃)₄)] / [Cu] [NH₃]₄ Equation (i)

It is known that 99.9 % of copper is in the form of ammonia complex and 0.01 % of it is found in its free state, the reaction will be:  

[Cu(NH₃)₄] / [Cu] = 0.999 / 0.001

Substituting the equation (i) we get:  

1.1 × 10¹³ = 0.999 / (0.001) (NH₃)₄

After solving for ammonia we get:  

[NH₃] = (999 / 1.1 × 10¹³)1/4

[NH₃] = 3.08 × 10⁻³ M

the answer is true.