140 NON-METALLIC ELEMENTS IN BINARY COMPOUNDSin air the peroxide, Na 2 O2, is formed. It is difficult to limit the
access of oxygen to burning sodium so as to obtain the ordinary
oxide, Na 2 O.
In the following preparation crude barium peroxide is treated
with hydrochloric acid to obtain a solution of hydrogen peroxide.
Crude barium peroxide invariably contains a little iron which
appears in the solution as FeCl3. The iron, however, is completely
precipitated as the insoluble hydroxide if an excess of barium
peroxide is used. The peroxide hydrolyzes, making the solution
basic.
BaO 2 + 2H 2 O ^ Ba(0H) 2 + H 2 O 2
2FeCl 3 + 3Ba(OH) 2 -> 2Fe(OH) 3 1 + 3BaCl 2
Pure barium peroxide hydrate BaO 2 -8H 2 O is precipitated when
barium hydroxide is added to a hydrogen peroxide solution.
Hydrogen peroxide is not a stable substance; its solution de-
composes slowly in any event into oxygen and water. This de-
composition is greatly hastened by suspended solid matter and by
hydroxyl ions; in the following preparation one should work to
minimize the amount of this decomposition.
After removal of impurities by filtration, a solution of barium
hydroxide is added whereby pure, crystalline barium peroxide
hydrate BaO 2 -8H 2 O is precipitated.
Hydrogen peroxide may be regarded as a weak acid. It is
excessively weak, the extent of its ionization being comparable
with that of water itself. Yet its acid character is manifest from
the way it reacts with barium hydroxide:
Ba(OH) 2 + H 2 O 2 -» BaO 2 1 + 2H 2 O
Were the barium peroxide soluble this reaction would shortly
come to equilibrium, but since the barium peroxide is very in-
soluble, the reaction is fairly complete. Sodium peroxide is
soluble, and it hydrolyzes very extensively, as would be expected
of the salt of so weak an acid; this is equivalent to the statement
that the neutralization of sodium hydroxide by hydrogen peroxide
is very incomplete.
Materials: 6N HC1, 67 cc.
barium hydroxide, Ba(OH) 2 -8H 2 O, 63 grams =
0.2 F.W.
crude BaO 2 40 grams,
ice.