BARIUM OXIDE AND BARIUM HYDROXIDE 199
(Note 9 (6), page 15). These crystals are efflorescent, hence, as
soon as the paper package is unwrapped, place them in a 2-ounce
cork-stoppered bottle.
QUESTIONS
- Explain why strontium carbonate, which is less soluble in
pure water than strontium sulphate, should dissolve readily in
dilute acids, while the latter salt will dissolve scarcely any more
in acids than in pure water.
- If a small quantity of a solution of strontium chloride were
added to a solution containing equimolal quantities of sodium
carbonate and sodium sulphate, what would be the precipitate
formed?
PREPARATION 22
BARIUM OXIDE AND BARIUM HYDROXIDE FROM
BARIUM CARBONATE, Ba(OH) 2 -8H 2 O
The commercial method of preparing calcium oxide (quicklime)
consists in heating calcium carbonate (limestone) in lime kilns.
Barium oxide might be made from barium carbonate according
to the same principle, except for the fact that the temperature
required for the decomposition of barium carbonate is so high as
to make such a method almost impracticable. This greater
stability of the barium salt is an illustration of the fact that barium
oxide is even more strongly basic than calcium oxide. The reac-
tion, BaCO 3 ?± BaO + CO 2 , is reversible, and in common with
other reversible reactions it may be made to progress in one
direction or the other by suitably altering the concentration of
the substances present in the reacting system. Of the three
substances involved in this reaction the only one which can be
removed during the course of the reaction is the carbon dioxide.
It is, however, not enough to let it merely pass off as a gas, be-
cause to escape from the crucible it will have to push back the
atmosphere. The pressure of carbon dioxide in equilibrium with
barium carbonate at 1350° is seen from the table to be but one-
half an atmosphere, that is to say, barium carbonate will decompose
until the atmosphere in the crucible contains about 50 per cent of
carbon dioxide and then the decomposition will stop. However,
at high temperatures charcoal reacts with carbon dioxide to form
carbon monoxide
CO 2 + C ^ 2CO
