Explain why `0.1M NH_(3)` solution:
a. Will precipitate `Fe(OH)_(2)` from `0.1M` soluton `Fe^(2+)`.
b. Will not precipitate `Mg(OH)_(2)` from a solution which is `0.2 M` in `overset(o+)NH_(4)` and `0.01M` in `Mg^(2+)`.
c. Will not precipitate `AgOH` from a solution which is `0.01M` in `Ag^(o+)`.

Explanation

a. `NH_(3)` provides sufficient `overset(Θ)OH` to excess `K_(sp)` of `Fe(OH)_(2)`.
b. `overset(o+)NH_(4)` makes a buffer solution, which limits `[overset(Θ)OH]` to such a level insufficient to cause precipitation of `Mg(OH)_(2)`.
c. `NH_(3)` forms `Ag(NH_(3))_(2)^(o+)` complex ion, which is soluble.