Question

How many moles of NH₃ must be added to 1 litre of 0.1 M AgNO₃ solution to reduce Ag⁺ concentration to 2 × 10^–7 M. K_d [Ag(NH₃)₂]⁺ = 7.2 × 10^–8.

Answer 1

[NH₃] = 0.189 M 

It is the concentration of free NH₃. 

[NH₃]_total = [NH₃]_free + [NH₃]_complexed = 0.189 + 2 × 0.1 = 0.389 M