IODIC ACID; IODINE PENTOXIDE 249Procedure: Dissolve 31 grams of potassium chlorate by warming
it with 100 cc. of water in a 1000-cc. flask. Add 36 grams of pow-
dered iodine and hang a small funnel in the neck of the flask to
prevent, to some extent, the escape of iodine vapor. Place a pan
of cold water close at hand; then add 1 cc. of 6N nitric acid to the
flask, and warm rather carefully until a brisk reaction commences.
Then allow the reaction to proceed so that violet vapors fill the
flask, but if iodine starts to escape through the funnel, check the
reaction by dipping the flask for a moment in the cold water.
After the reaction has moderated warm the solution until the
iodine color has disappeared, and then boil it for about 10 minutes
to expel most of the free chlorine. The solution now contains a
considerable quantity of iodic acid in addition to the potassium
iodate. Add a solution of potassium hydroxide until the neutral
point is just reached (test by dipping a stirring rod in the solution
and touching it to litmus paper). Allow the solution to cool,
collect the crystals of potassium iodate, and evaporate the mother
liquor to obtain another crop of crystals. Purify the entire prod-
uct by dissolving it in four times its weight of hot water, cooling,
and collecting the crystals. Dry the product and preserve it in a
2-ounce cork-stoppered bottle.QUESTIONS- Explain the secondary reaction of the foregoing preparation
in which chlorine reacts with iodine. - From knowledge of the reactions of chlorine and bromine
predict how iodine would react with a KOH solution. Find from
reference books whether this prediction is borne out by the facts.
PREPARATION 38
IODIC ACID; IODINE PENTOXIDE, I 2 O 5
Iodine pentoxide is a white solid substance that, at ordinary
temperatures, is entirely stable. It cannot be prepared by direct
synthesis from iodine and oxygen, because when cold the elements
combine too slowly, and when heated the compound is unstable.
It may be readily prepared by the direct oxidation of iodine by
means of strong oxidizing agents, such as concentrated nitric acid
or chlorine. One method for the oxidation of iodine has already
been illustrated under the preparation of potassium iodate, but