312 ELEMENTS OF GROUP VWhat secondary reaction accounts for the formation of the precipi-
tate if its formula is Sb 2 S 5?- Actually the precipitate is a mixture of Sb 2 S 6 and Sb 2 O 5 or an
oxysulphide. Write an equation for the change of Sb 2 S 6 to Sb 2 OB
in the presence of NaOH solution, and show that Na 2 S ought to
repress the change to the oxide. - What general principle is illustrated in the fact that Sb 2 S3
dissolves much less readily than Sb 2 S 5 in Na 2 S solution?
PREPARATION 58
ANTIMONY PENTASULPHIDE, Sb 2 S 6
This compound cannot be prepared directly from the trisulphide
and sulphur, because it is decomposed at a temperature below that
at which the latter substances would react. As has just been seen,
however, the higher sulpho-salt of antimony can be readily pre-
pared in the wet way; and this, on decomposition with a dilute
acid, yields antimony pentasulphide. This substance is used in
vulcanizing rubber and produces a red colored product.
Materials: sodium sulphantimonate, Na 3 SbS4-9H 2 O, from pre-
ceding preparation, 48 grams = 0.1 F.W.
6N H 2 SO 4 , 108 cc.
Apparatus: 2-liter common bottle.
5-inch funnel.
Procedure: Dissolve the sodium sulphantimonate obtained in
the last preparation, and dilute with 1 liter of cold water. Add the
sulphuric acid and 350 cc. of water to the large common bottle.
To this add slowly, and with constant stirring, the solution pre-
pared above. Fill the bottle with water and stir thoroughly. Let
the precipitate settle, draw off the liquid, and wash by decantation
until the wash water no longer gives the test for a sulphate with
barium chloride. After the last washing let the solid settle for
some time, draw off as much as possible of the clear liquid, and
transfer the sludge to a large plain filter (Note 4 (c), page 7; do
not omit to reenforce the point of the filter) to drain for 12 hours
or longer. Without removing the pasty antimony sulphide,
open out the filter on paper towels, and leave it on a shelf above
the steam table where the temperature does not rise above 50°.
When the product is completely dry, detach the hardened lumps