DIFFERENT BEHAVIOR OF OXIDES AND PEROXIDES 159
The brown residue is anhydrous cupric chloride in which the
oxygen of cupric oxide has been replaced by an equivalent amount
of chlorine.
CuO + 2HC1 -> H 2 O + CuCl 2
The primary valence of all the elements concerned in this re-
action has remained unchanged, the elements have simply "ex-
changed partners," the type of reaction being metathesis. This
instance is typical of the reaction of metal oxides with acids.
The oxygen is simply exchanged for an equivalent amount of acid
radical and the valence of the metal is not altered.
DIFFERENT BEHAVIOR OF OXIDES AND PEROXIDES
Hydrogen peroxide, H 2 O 2 , contains, for a given amount of hy-
drogen, twice as much oxygen as does water, and the additional
amount of oxygen is held in an unstable state of combination.
Pure hydrogen peroxide is explosive; in dilute solution it gives off
one-half its oxygen more or less rapidly but not explosively. In
pure solutions this decomposition proceeds so slowly that it is
practically imperceptible; but many substances act as cata-
lyzers for the reaction, notably platinum and manganese dioxide.
- To 10 cc. of a 3 per cent solution of hydrogen peroxide
in a test tube, add a pinch of powdered manganese dioxide.
Note that a vigorous effervescence ensues and that the
escaping gas will cause a glowing splinter to burst into flame.
- Test for Hydrogen Peroxide. To 2 cc. of 3 per cent
hydrogen peroxide solution add 18 cc. of water, thus making
the volume 20 cc. Mix thoroughly, pour about 15 cc. of the
solution into a test tube, and add 1 cc. of a solution of titanium
sulphate.* Note the characteristic yellow color. This is one
of the standard tests for hydrogen peroxide. Determine the
delicacy of the test by repeating it successively with smaller
and smaller amounts of hydrogen peroxide, as follows: take
2 cc. of the remainder of the diluted solution and dilute it to
20 cc. by adding 18 cc. of water. Test 15 cc. of this solution
by adding 1 cc. of titanium sulphate, and reserve 2 cc. for
further dilution. Proceed in this way with successive dilu-
- Prepared by fusing 1 part of titanium dioxide with 15 to 20 parts of po-
tassium bisulphate and dissolving the mass in 500 cc. of cold 6 N sulphuric
acid.
