METATHESIS 107dition after the reaction as they were in the beginning, and it is
exactly this fact which is emphasized by this manner of writing
the equation, for these ions simply appear beside the oppositely
charged ions with which they were originally paired and nothing
happens to them. They are placed adjacent to each other, show-
ing that after the changes have taken place they are capable of
balancing each other electrically.
The arrow is indicative of the real reaction, and the formulas
of the components which do change are placed in the line of the
arrow and constitute the equation Ag+ + Cl~ —» AgCl, which, for
convenience, was arranged in a vertical line.
Experiments have shown that any ionized silver salt, e.g.,
Ag 2 SO 4 , AgC2H 3 O 2 , AgC10 3 , may be substituted for AgN0 3 , and
any ionized chloride may be substituted for the NaCl, and the same
results will be obtained. The union of Ag+ and Cl ~ ions to form
insoluble AgCl is in no wise affected by the other ions with which
these ions are at the outset in electrical balance. These other
ions will simply remain in the solution unless they, too, are the
ions of some insoluble salt, for example, BaSO4 or an undissociated
molecule like H 2 O.
The above principles do not apply solely to silver salts and chlo-
rides, but to all solutions. Reference to the table of solubilities
on page 364 will inform one whether or not a precipitate will be
formed when any two solutions of electrolytes are mixed together.
PROBLEMS
Divide a good-sized sheet of paper into two columns; in the
left-hand column describe the observable effects of bringing
together the substances noted in the cases below; in the right-hand
column write the equation in the fully ionized intersecting form,
following Rules 1 to 8, inclusive, on page 104. In the following,
unless otherwise specified, the formula stands for the substance
in a fairly dilute solution. The table of solubilities in the Ap-
pendix should be consulted.
- AgNO 3 + NaCl.
- AgCl (solid) + Nal.
- BaCl 2 + Na 2 CO 3.
- Pb(NO 3 ) 2 + H 2 SO 4.
- PbSO 4 (solid) + Na 2 S.