Synthetic Inorganic Chemistry

CHAPTER X

ELEMENTS OF GROUP V OF THE

PERIODIC SYSTEM

In this group, as in Groups III and IV, the difference in prop-
erties between the elements of Families A and B is not so striking
as in Groups I and II (or as in Groups VI and VII), and the
whole group is considered under the same heading. It is also true
that the elements of Family A, that is, vanadium, columbium, and
tantalum, are of comparatively infrequent occurrence, and are
given no attention in this course. On the other hand all the ele-
ments of Family B are of frequent occurrence
and considerable importance.
The characteristic valence of the group is 5,
corresponding to the oxide M 2 OB, but the ele-
ments likewise exhibit a valence of 3 in the
oxide M2O3. It is noteworthy that the valence
is nearly always either 3 or 5.
D It is true in this group, as well as in Group
IV, that the acid-forming properties are most
marked in the elements of low atomic weight
(nitric acid is one of the strongest acids), and
decrease with increasing atomic weight, whereas
the base-forming properties are most strongly
developed with the elements of high atomic
weight.

PREPARATION 52

ORTHO-PHOSPHORIC ACID, H3PO4

Pure phosphoric acid is prepared commer-

cially by burning phosphorus in air to form

phosphorus pentoxide and then treating this

compound with water. On a laboratory scale it is more convenient

to oxidize the phosphorus with a solution of nitric acid.

The solution first obtained by the action of dilute nitric acid

298

FIG. 25