194 ALKALI AND ALKALINE EARTH METALS
the solution into the evaporating dish and evaporate it to dryness
on the steam bath (see Note 6 (6), page 12). Pulverize the dry
salt and put it in a 2-ounce cork-stoppered bottle.
QUESTIONS
- What products would be formed if bromine were added to
a solution of sodium hydroxide instead of ammonium hydroxide
(a) if the solution were kept cold? (6) if it were heated?
- Add about 10 drops of bromine to 10 cc. of a cold 3.ZV
sodium hydroxide solution. Add this gradually to a solution
of ammonium hydroxide, made by diluting 1 cc. of the 6 N reagent
with 10 cc. of water. Determine what gas is given off.
- What fraction of the entire amount of ammonium ion used is
lost through formation of nitrogen gas when ammonium bromide
is made by the action of bromine on ammonium hydroxide?
- Why cannot hydrobromic acid be prepared from potassium
bromide by a method analogous to that used in the preparation of
hydrochloric acid?
PREPARATION 20
STRONTIUM HYDROXIDE FROM STRONTIUM SULPHATE,
Sr(OH) 2 -8H 2 O
One of the most important sources of strontium is the mineral
celestite, SrSO*. By reduction with charcoal this can be con-
verted into strontium sulphide,
SrSO 4 + 4C = SrS + 4CO
and the strontium sulphide, by treatment with copper oxide and
water, can be made to yield strontium hydroxide,
SrS + CuO + H 2 O = Sr(OH) 2 + CuS
Copper oxide is, in the ordinary sense, insoluble; nevertheless, in
contact with water it does yield to an infinitesimal extent the ions
of cupric hydroxide.
CuO + H 2 O ^± Cu(OH) 2 ^ Cu++ + 2OH"
Since copper sulphide is a far more insoluble substance than
copper oxide, it follows that the few Cu++ ions from the latter
unite with the S~~ ions from the strontium sulphide to form
copper sulphide, which precipitates continuously, while the
