248 OXY-ACIDS AND SALTS OF THE NON-METALSQUESTIONS- Tabulate the solubilities at high and low temperatures of
the salts concerned, and arrange a flow sheet of the method to
be followed if the mother liquors are worked over. - The commercial method of making potassium chlorate is
by the electrolysis of a potassium chloride solution. What are
the primary products formed at the two electrodes? Explain how,
when the primary products are allowed to mix in the cell, the re-
actions are similar to those of this and the preceding preparations.
PREPARATION 37
POTASSIUM IODATE, KIO 3
As is well known, the chemical affinity of the halogens for
hydrogen or positive elements decreases in passing from fluorine
to iodine; but the affinity for oxygen increases in this order, so that
iodates and iodic acid (I2O6) are more stable than chlorates and
chloric acid (CUCX). Use is made of this fact in the following
preparation, in which the total change is represented fairly closely
by the equation
KCIO3 + |I 2 -»• KIO3 + |C1 2
The actual reaction, however, is not so simple as this. The
presence of a small amount of acid is necessary to make it take
place. This acid gives rise to a little free chloric acid, which is a
far stronger oxidizing agent than potassium chlorate, and oxidizes
iodine to iodic acid. The latter acid reacts with more potassium
chlorate and thus chloric acid is regenerated. It will be noticed
that in carrying out the following directions more iodine is taken
than is necessary to react with the potassium chlorate according
to the equation given above. This excess of iodine is oxidized to
iodic acid by a part of the free chlorine which is represented in the
equation as escaping.
Materials: potassium chlorate, KCIO3, 31 grams = 0.25 F.W.
iodine, 36 grams.
Apparatus: 1,000-cc. flask.
short-stemmed funnel.
pan of cold water.
suction filter and trap bottle.
iron ring and ring stand.
Bunsen burner.