REACTIONS OF OXIDATION AND REDUCTION 121PROBLEMS
Describe observable effects and write the fully ionized equa-
tion for the following cases, when the reagent (second formula)
is added (a) in limited amount, and (6) in excess.
- ZnSO 4 + NH 4 OH.
- CuCl solid + NH 4 OH.
- Ag2SO 4 + NH4OH.
- (Cu4NH 3 )S0 4 + HNO 3.
- (Ag-2NH 3 )C1 + HNO 3.
- AgNO 3 + KI.
- AgCl (solid) + NaCl (saturated solution, in very large
excess). - AgNO 3 + KCN.
- CuCl solid + KCN.
REACTIONS OF OXIDATION AND REDUCTION
Ionic Displacement. Electromotive Series. When a strip of
zinc is placed in a solution of copper sulphate, it is noticed that
a spongy deposit of copper metal soon appears on the surface of
the zinc, and that the solution loses its blue color. Then if the
solution is tested for the presence of copper and zinc ions by add-
ing ammonium sulphide, it is found that this reagent gives a white
precipitate. This test shows that copper ions are now absent
and that zinc ions are present because we know ammonium sul-
phide will precipitate black copper sulphide from a solution of
copper ions, and white zinc sulphide from a solution of zinc ions.
Since ordinary pieces of metal are not charged, it is obvious that
the reaction consists in a transfer of the positive charges of
the copper ions to the zinc atoms, or, more strictly, of negative
electrons from the zinc atoms to the copper ions:
Zn°->Zn+++ 20
SO 4 "" Cu++
1
Cu°
The small zero mark ° is not essential; it may be used when it is
desired to attract particular attention to the fact that the atom to
which it is attached is not electrically charged. Since the SO 4 ~~
ions take no part in the above reaction beyond balancing by their