Synthetic Inorganic Chemistry

COMPLEX IONS 119

If the two sets of ionic equations are now put together it is

seen that 2NH 4 + and 2OH ~ have been left and these will combine

to form 2NH4OH, which will cancel. Thus the net result becomes:

Cu++ SO 4 ~~

4NH 4 OH ;=± 4NH 3 + 4H 2 O

Cu-4NH 3 ++

the resulting solution containing ionized (Cu4NH 3 )S0 4 and only-
enough excess of ammonia to prevent the dissociation of this
ammonia te.
It is interesting to note that, if freshly precipitated and thor-
oughly washed Cu(OH) 2 is treated with ammonia, a similar deep
blue solution is obtained, but in this case the negative ions are
hydroxyl instead of sulphate. Ammonio-copper hydroxide is
very soluble and very highly ionized, and the solution compares
in basic strength with one of sodium hydroxide.
It is most interesting that the addition of ammonia to the simple
ions of several of the heavy metals produces similar effects. The
base-forming character of the metals seems thereby to be greatly
strengthened. The following list gives the metals which possess
this property to a marked degree and also the formulas of their
ammonio ions:

copper (ous) Cu-2NH 3 + colorless

silver

zinc

cadmium

nickel

cobalt

(ic)

(ous)

Cu-4NH 3 ++

Ag-2NH 3 +

Zn-4NH 3 ++

Cd-4NH 3 ++

Ni-4NH 3 ++

Co-4NH 3 ++

deep blue
colorless
colorless
colorless
blue
red
(ic) Co-6NH 3 +++ brownish yellow
Aluminum, iron, tin, lead, and some other metals do not have
the power of forming such ammonio compounds.
Complex Negative Ions. When an equivalent amount of sodium
cyanide is added to a solution of silver nitrate, quantitative pre-
cipitation of silver cyanide takes place

Ag+ N(V

CN" Na+

1

AgCNj