256 OXY-ACIDS AND SALTS OF THE NON-METALS
(6) Stir 5 grams of bleaching powder with 5 cc. of water.
It cannot be seen to dissolve at all. Add 1 cc. of the suspen-
sion to 100 cc. of water, and note that it imparts a cloudiness to
the whole so that it cannot yet be told whether any has dis-
solved. Pour the rest of the undiluted suspension into a
filter and collect the filtrate. To 1 cc. of the filtrate add a
few drops of QN HC1. The color and odor of chlorine are
perceived.
Bleaching powder is prepared by treating slaked lime, Ca(OH) 2 ,
with chlorine, and it is essentially a mixture of equivalent amounts
of calcium chloride, CaCU, and calcium hypochlonte, Ca(OCl)2.
The formula of the solid material is written CaOCU, indicating
the belief that it is not a mixture of two salts, but rather a mixed
salt in which each molecule contains a chloride and a hypochlonte
radical.
Calcium chloride and calcium hypochlonte are both extremely
soluble; but bleaching powder always contains a considerable
excess of calcium hydroxide which has not reacted with the
chlorine, and also a good deal of calcium carbonate. That hypo-
chlorite and chloride dissolve freely out of the bleaching powder is
shown by the action with hydrochloric acid.
2HC1 + Ca(OCl)Cl -»• CaCl 2 + H 2 O + Cl 2
(c) Soak a piece of colored cotton cloth in one-half of the
filtrate obtained in (6). Different colors bleach with varying
ease, but it is probable that this one will decolorize hardly
perceptibly. Remove the cloth with the solution still cling-
ing to it and immerse it in very dilute H2SO4 (1 cc. of 6N acid
to 50 cc. of water). The color now rapidly disappears.
Add 5 cc. of 6 N NaOH to the other half of the filtrate from
the bleaching powder suspension. A voluminous white preci-
pitate is formed. Soak another piece of cloth in this sus-
pension and note that it is not bleached at all.It is a well-known fact that dry chlorine does not bleach dry
cloth, but that chlorine water bleaches it easily. It is known that
chlorine hydrolyzes (see Preparation 36), and the bleaching is
attributed to the hypochlorous acid, which, on account of its
instability, is a strong oxidizing agent and oxidizes the colored
substance to a colorless one.