ANHYDROUS STANNIC BROMIDE 275quietly. Continue the action until all the tin has disappeared
and the tin tetrachloride has been caught in the receiving flask.
Remove the neck of the retort from the condenser, and insert
instead a stopper with a tube leading to the bottles already used
for absorbing waste chlorine. Close the side arm of the receiving
flask and, with the condenser still in the same position, boil the tin
tetrachloride .until it is colorless (it contains a large amount of
dissolved chlorine and, on boiling, this reacts with the tin foil).
Change the position of the flask and condenser, and distil the tin
tetrachloride into the prepared container. During the distillation
this container should not be open to the air, but should be con-
nected by a tube to the absorbing bottles already used. When
the liquid is all distilled, seal the neck of the container at a blast
lamp, so that the preparation can be preserved out of contact
with the air.
QUESTIONS- What is the purpose of the wash bottles as arranged for the
chlorine gas? - Suggest how hydrated stannic chloride, SnCl4-5H 2 O, might
be made, starting with stannous chloride. - What happens if hydrated stannic chloride is heated? (Com-
pare aluminum chloride and bromide, Preparations 25 and 26.)
PREPARATION 45
ANHYDROUS STANNIC BROMIDE (TIN TETRABROMIDE), SnBr 4
(This preparation must be started at the beginning of the
laboratory period and must be completed the same day. Perform
under the hood.)
There are two series of compounds of tin and the halogens;
those related to stannous oxide, SnO, in which the metal has a
valence of 2 (stannous salts), and those related to stannic oxide,
SnO 2 , in which it has a valence of 4 (stannic salts). The com-
pounds with lower valence are usually prepared by the action of
the halogen acids on the metal. Stannous chloride, for example,
is formed when hydrochloric acid reacts with tin. Stannic salts,
on the other hand, are prepared by the reaction of tin and the free
halogen. In this preparation stannic bromide results from the
reaction of bromine and tin. The reaction between the two ele-