CALCULATE THE SOLUBILITY OF CuBr in 0.69 M NH3

Answer 1

...CuBr(s) + 4NH3 ==> Cu(NH3)4^2+ + Br^-
I....solid....0.69.....0............0
C....solid.....-4x.....x............x
E....solic....0.69-x...x............x

What we usually do is to say that this reaction goes essentially to completion since Kf for the complex is such a large number of 1.1E13 (you should look this up in your text/notes and use what it shows). So we redo the above ICE chart but work backwards (from right to left an start with 0.69 M for the complex.
---------------------------------
I.....0.......0......0.172....0.172
C.....x.......4x..... -x........-x
E.....x.......4x.....0.172-x..0.172-x

Substitute E line into K expression and solve for x.