SODIUM HYPOCHLORITE. 115
and the latter being a much stronger oxidizing agent than sodium hypochlo-
rite, or the hypochlorite ion, it oxidizes chlorite and hypochlorite ions into
chorate ions:
2 HC10 + CIO" = C1O 3 - + 2 HC1,
3 HC10 + Cl- = C1O 3 - + 3 HC1.
Heating accelerates these reactions.
The raw materials necessary for these experiments can be prepared more
conveniently by the electrolysis of alkali chloride solution than by purely
chemical means. At the anode, chlorine is the primary product; sodium is
the primary product at the cathode, but it immediately decomposes water
to give sodium hydroxide and hydrogen. The products formed at the elec-
trodes react together in the manner shown above when they are allowed to
mix by diffusion.
The process as outlined above is, however, interfered with somewhat by
the progress of certain secondary reactions. First, the hydrogen produced
at the cathode reduces the hypochlorite, and to some extent the chlorate,
to chloride. Since only the discharged hydrogen atoms, which have not
yet combined to form molecules, cause the reduction, it is advantageous
to restrict the formation of hydrogen to as small an area as possible; by
this means the formation and escape of gaseous hydrogen is favored. In
other words, the current density at the cathode must be kept high. To
further avoid cathodic reduction, the deposition of a thin skin — a "dia-
phragm" — of hydrated chromic oxide on the metal of the cathode works
excellently; this can be most simply accomplished by the electrolytic reduc-
tion of a little alkali chromate which is added to the electrolyte.
Second, the C1O~ and C1O3~ ions, that are formed in the process, carry a
part of the current, and when they become discharged at the anode, they
then react with water to form the free acids and oxygen. The current which
serves to discharge these ions is, therefore, wasted. The loss can be lessened
by using a high anodic current density.
Both of these secondary reactions become more pronounced as the elec-
trolysis progresses, i.e., as the concentration of the chlorate or the hypochlo-
rate becomes greater. This explains why the yield for a given amount of
current gradually grows less with a long-continued electrolysis.
Sodium Hypochlorite. A. The arrangement of the electrical
connections, the external resistance, and the measuring instru-
ments is that described in No. 14 (cf. Fig. 9). Place the beaker
containing the electrolyte, which is a solution of 88 g. of sodium
chloride in 500 c.c. of water (3-normal), inside a larger beaker
containing ice water. For electrodes use two sheets of platinum
of known area, e.g., 30 sq, cm. The anode reaches only into the
upper part of the solution, the cathode nearly to the bottom with
the attached wire insulated by being passed through a glass tube.
The hydrogen bubbles rising from the cathode cause stirring. The