316 ELEMENTS OF GROUP V
excess of 6N HNO 3 (10-15 cc.) and note that red gases are
evolved in each case.
(a) A clear solution results. Evaporate this until excess
of volatile nitric acid is expelled, but do not exceed a tem-
perature of 180°. A sirupy liquid is left which dissolves in
water to give an acid solution.
(6) A clear solution is left. Evaporate this carefully to
dryness. A white solid is left which dissolves in water to give
an acid solution.
(c) The metal disappears and a white powdery solid re-
mains in the liquid. This solid is insoluble in nitric acid or
water.
(d) A clear solution results out of which, after concentrat-
ing and cooling, clear crystals of a salt separate. These crys-
tals dissolve in a little water acidified with HN0 3 to give a
clear solution, but a white precipitate is formed if the solution
is diluted with a large amount of water.Phosphorus, arsenic, and antimony are oxidized by nitric acid to
hydrated forms of the pentoxides, giving respectively: phosphoric
acid, H3PO4, which is very soluble in water and a fairly strong acid;
arsenic acid, H3ASO4, which can be dehydrated to the oxide AS2O6
which will dissolve in water again to form the acid; meta-anti-
monic acid, which is a very weak and insoluble acid. Bismuth is
oxidized only to the trivalent condition; Bi 2 O3 is basic and forms
the salt Bi(NO 3 )3 with the excess of HN0 3. This salt hydrolyzes
very easily to an insoluble salt, and with a large amount of water it
hydrolyzes completely to Bi(0H) 3.
- Sulphides and Thio-Salts. Pass hydrogen sulphide
into hot dilute solutions of arsenic, antimony, and bismuth
trichlorides in separate test tubes. Note that yellow, orange,
and black precipitates respectively are formed. Let the
precipitates settle to the bottom of the tubes, pour off the
liquid, and treat the solid with sodium polysulphide (Na 2 S
solution in which sulphur is dissolved) in each case. The
yellow and orange precipitates dissolve; the black one does
not. To the two solutions add 6N HC1 in excess and note
that yellow and orange precipitates respectively are again
thrown out.